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000
FXUS65 KCYS 251745
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1145 AM MDT WED MAY 25 2016

.UPDATE...
Issued at 1121 AM MDT Wed May 25 2016

Latest radar trends showing isolated showers developing across
southeast Wyoming where we had dry conditions in the forecast.
Went ahead and added 20 percent pops in the forecast for this
late this morning and afternoon. Updates have been sent.|

&&

.SHORT TERM...(Today through Friday)
Issued at 330 AM MDT Wed May 25 2016

Predawn water vapor loop depicted a positively-tilted upper trough
from south central Canada across the northern Rockies to a low off
the central California coast. An active southwest flow aloft was
transporting weak shortwave disturbances northeast across the Four
Corners...central Rockies and plains. A fast 250 mb jet max and
shortwave aided in the development of several convective clusters
over the Great Plains. Converging outflow boundaries from convection
over northeast Colorado generated a narrow line of thunderstorms
over the southern Nebraska Panhandle shortly after midnight. This
activity will soon enter western Nebraska. A quasi-stationary
surface front extended from eastern South Dakota into western
Nebraska then south through the high plains. A moist boundary and
light winds over the Nebraska Panhandle resulted in a growing area
of stratus.

Good run-to-run consistency with the numerical models as the upper
trough to the west slowly translates east across the Rockies and
high plains through Friday. The front draped across the high plains
will also shift east with its moist unstable air mass today. The
next shortwave lifting northeast from the Four Corners combined
with the weak surface trough will aid in the development of widely
scattered afternoon showers and thunderstorms. The HRRR and RAP
models indicate cell motion to the east-southeast. There may be a
few stronger cells producing small hail and gusty winds, especially
east of the Laramie Range. High temperatures today will be near
seasonal normals with 60s to mid 70s valleys and plains, and 40s
and 50s for the high country.

The coverage of showers and thunderstorms will increase Thursday
and Friday as the upper low over southern California tracks east-
northeast across the Four Corners, Colorado and central High Plains.
Model QPF has been consistent showing between a quarter and a half
inch of liquid equivalent precipitation. Locally heavier amounts
will be possible with thunderstorms. Snow levels will drop to
8500 feet Thursday night, with scattered showers producing a few
inches of snow over the higher peaks of the Snowy and Sierra Madre
mountains. The greatest severe potential Thursday and Friday will
be focused over the Great Plains, with a marginal risk for a few
strong to possibly severe thunderstorms south and east of a line
from Chadron to Laramie. High temperatures for the high plains
will cool back into the 60s on Friday, with 40s and 50s for higher
elevations.

.LONG TERM...(Friday night through Tuesday)
Issued at 1124 PM MDT Tue May 24 2016

The main weather story through the long term forecast period will
be near normal temperatures with isolated to scattered showers and
thunderstorms. Generally looking at an upper level trough across
the western conus through early next week. Chances for showers and
thunderstorms will occur nearly each day with the main chances in
the afternoon. Several shortwaves will move across the forecast
area this weekend and into early next week but timing is somewhat
in question. Placement and timing will one of the main drivers as
to how much precipitation falls. Currently the expectation is for
weak upper forcing with any given shortwave and limited moisture
availability. generally not looking for widespread or heavy
precipitation through early next week, of course with thunderstorm
activity a few localized places may see some heavier rains.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1142 AM MDT Wed May 25 2016

The main concern to aviation ops this afternoon will be the
isolated shower/thunderstorm activity that is already developing
across southeast WY & west NE. Coverage and intensity will be
limited so sufficient to just include mention of VCTS at most TAF
sites. Will of course monitor these trends and amend if
thunderstorms become more imminent. Thunderstorm activity will
dissipate quickly this evening, giving way to just some passing
mid/high-level clouds overnight.

&&

.FIRE WEATHER...
Issued at 245 AM MDT Wed May 25 2016

Cool and moist conditions will preclude fire weather concerns
through the end of the week. Scattered showers and thunderstorms
will provide wetting rains, with snow showers for elevations above
9000 feet.

&&

.HYDROLOGY...
Issued at 245 AM MDT Wed May 25 2016

Cool temperatures will persist through the end of the week with
morning lows in the upper 20s-lower 30s and afternoon highs in the
mid 40s-lower 50s for the mountains. These cool temperatures will
slow the snowmelt runoff into the streams and tributaries of the
Upper North Platte and Laramie rivers. A low pressure system moving
across Colorado Thursday and Friday will produce a good coverage
of showers and thunderstorms, with precipitation amounts from a
quarter to half inch. Locally higher amounts will be possible with
thunderstorms. The higher peaks of the southeast Wyoming mountains
may receive a couple inches of snow. Will be monitoring the impacts
of rain on snow for area rivers, creeks and streams this weekend.

&&

.CYS Watches/Warnings/Advisories...
WY...None.
NE...None.
&&

$$

UPDATE...GCC
SHORT TERM...MAJ
LONG TERM...SML
AVIATION...CAH
FIRE WEATHER...MAJ
HYDROLOGY...MAJ



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000
FXUS63 KUNR 250555
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1155 PM MDT TUE MAY 24 2016

.UPDATE...
Issued at 811 PM MDT Tue May 24 2016
Made a few little changes to tonight to increase pops for the next
few hours over northeastern Wyoming as convection is redeveloping
as the wave pushes through. Also increased pops over south central
as MCS begins to develop and move east. Temperatures appear to
remain on track...but adjusted the wind direction to account for
the latest trends.

&&

.SHORT TERM...(This Evening Through Wednesday Night)
Issued at 218 PM MDT Tue May 24 2016

Upper low spins over southern Saskatchewan, with southwest flow
and a 70-80 kt jet over the CWA. At the surface, there`s an area
of high pressure over western ND and low pressure over southern
WY. Winds across the CWA are southeasterly, bringing in more moist
air with dew points in the 40s across central/western SD. Dew
points are in the 30s across northeastern WY, with cooler temps in
the 60s. Clouds are increasing, and radar is showing some showers
over portions of the area.

Upper divergence and energy associated with the low pressure system
will aid in thunderstorm development this afternoon and evening,
with the best energy over Nebraska. Instability is marginal over
much of northeastern WY and western SD, with the best MLCAPE near
1000 J/kg along the Nebraska border. However, 0-6km shear up to 60
kts may result in a few severe thunderstorms. Precipitable water
this evening will be around 150% of normal. Forecast soundings
indicate the biggest threats will be strong winds and heavy rain,
although large hail cannot be ruled out, especially near the
Nebraska border. Hi-res convective models are showing a band of
thunderstorms moving through the CWA this evening, shifting east of
the area by morning. Additionally, there may be a secondary batch of
storms that moves through the northeastern WY/Black Hills area as
more shortwave energy pushes into the region.

On Wednesday, NAM and GFS are showing the upper low splitting into
two lows, while the ECMWF has a strong wave instead of a closed low.
Nonetheless, this low/wave will help produce more showers/storms
across the area, with better chances across northwestern SD. Surface
low will move through SD and drag a cold front through the area.
Highs will range from the 60s across the western CWA to the lower
80s across south central SD. With dew points in the mid to upper 50s
across central SD, models are showing MLCAPE of 1000-2000 J/kg
there. Best 0-6 km shear of 35-45 kts is also over south central SD,
and so that area will have the greatest chance in our CWA of any
thunderstorms becoming severe.

.LONG TERM...(Thursday Through Tuesday)
Issued at 218 PM MDT Tue May 24 2016

Persistent upper level troughing over the northwest
CONUS will keep active southwest flow across the Northern Plains
through the Memorial Day weekend. Periodic shortwave energy will
eject out of the trough, keeping a daily chance of showers and
thunderstorms in the forecast through the holiday weekend.
Temperatures will be near seasonal averages, with highs each day
generally in the mid 60s to upper 70s. Lows at night will be in the
40s to mid 50s.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1151 PM MDT Tue May 24 2016

Sct showers and thunderstorms will continue to move east across
the area overnight. MVFR conditions will be possible near any
precipitation. A cold front will move into the area early this
morning with mvfr to ifr conds possible across ne wy into nw sd.
Conds will trend vfr all locations later this morning into the
afternoon.


&&

.UNR Watches/Warnings/Advisories...
SD...None.
WY...None.
&&

$$

Update...MS
SHORT TERM...Pojorlie
LONG TERM...13
AVIATION...15




000
FXUS65 KCYS 250532
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1132 PM MDT TUE MAY 24 2016

.UPDATE...
Issued at 1006 AM MDT Tue May 24 2016

Ongoing forecast looks to be in good shape. did pull severe
thunderstorm wording back west a little bit more to include
Cheyenne. Current SPC Mesoanalyst page showing a slight cap still
right along the east slopes of the Laramie Range that breaks
around 17Z. Latest EMCWRF shows convection beginning shortly after
that time. Could be looking at severe thunderstorms initiating
around 20-21Z along the I-25 corridor (Chugwater) with storms
congealing into a possible squall line late afternoon into the
central and northern Panhandle towards 00Z.

&&

.SHORT TERM...(Today through Thursday)
Issued at 145 AM MDT Tue May 24 2016

The main concern with this portion of the forecast is where the
convection will initiate today and where the best chance of severe
storms will be.

Today-Tonight:
Latest water vapor loop continues to show 60 to 70 kt of jet energy
moving out of the southwest with broad scale upper level diffluence
developing over the Rockies. It appears the leading edge of the
potential vorticity anomaly (pva) is in Northern Utah. The main
challenge for today will be where this pva ends up this afternoon
and where the convection will initiate. Latest NAM solution is
showing this anomaly affecting the northern Laramie Range early
this afternoon. Interestingly enough the experimental HRRR/local
WRF solutions are showing the initial development of the
convection this afternoon taking place in the northern Laramie
Range as well around 18-19z. If this ends up panning out, then we
may have an early threat for strong to severe storms further north
around Lusk and the Northern Panhandle. However, I am not as
confident that the low level moisture will get that far north with
these storms possibly having higher bases. However, the low level
shear (0-1km) is around 20 to 25kts at Chadron near a boundary
which may favor some brief high based tornados. However, the main
threat still appears to be large hail and damaging wind.

Further south, it is a matter of timing of when the second piece
of pva moves into northern Colorado and southern Wyoming. The
local WRF/HRRR are both showing convection developing by 21z.
These storms will certainly have more moisture to work with which
will tend to favor lower cloud bases especially in the southern
Panhandle. Effective bulk shear values will generally range from 45
to 50 kt, which will also favor rotating updrafts. A couple of
these storms may also have a threat of becoming supercellular with
even a possible brief tornado.

Most of this convection should move northeast at 30 to 35 mph, but
the right moving supercells will generally move east at 30-40 mph.

All of this convection may merge into a broken squall line between
00z-03z, but most of it should exit the forecast area by around
03z.

Tuesday night-Thursday:
We are a bit worried about some gusty winds following the line of
convection this evening. Models are showing good downward vertical
motion which may allow for some good mixing before sunset. Beyond
Tuesday night more upper level energy is progged to dive southeast
from Montana on Wednesday. Ahead of this upper level energy we will
see good downslope flow which will favor rather mild temperatures
before the next wave moves through the Rockies on Thursday and
brings cooler and wetter conditions.

.LONG TERM...(Thursday night through Monday)
Issued at 330 AM MDT Tue May 24 2016

The medium range models have been consistent with the timing and
track of the upper low affecting the central Rockies and plains
Thursday night and Friday. This system will widespread showers and
thunderstorms, with snow showers as snow levels drop to 9000 feet.
Refer to the Hydrology section for details on precipitation amounts.
It will be cooler than normal with highs in the 60s to near 70,
with 40s and 50s for the high country.

Precipitation coverage decreases somewhat this weekend and early
next week as a short wave ridge develops along the Front Range
ahead of the next upper trough moving into the Northwest CONUS.
The best chances for convection will focus over the higher terrain,
with more isolated coverage across the plains. The southwest flow
aloft between a upper ridge over the central CONUS and upper trough
axis to over the Northwest CONUS will allow temperatures to warm
to seasonal normals with highs in the mid 60s-mid 70s, and mid
50s-mid 60s for the high country.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1124 PM MDT Tue May 24 2016

Isolated showers and thunderstorms over southeast Wyoming and the
western Nebraksa Panhandle as of 0530Z should end by 0800Z.
Outside of showers and thunderstorms, light winds and vfr can be
expected through the taf period. Isolated showers and
thunderstorms are expected Wednesday afternoon.

&&

.FIRE WEATHER...
Issued at 145 AM MDT Tue May 24 2016

Fire weather concerns will be minimal during the next several days
due to chances of precipitation through the period and mostly wet
fuels from greenup.

&&

.HYDROLOGY...
Issued at 300 AM MDT Tue May 24 2016

Cool temperatures will persist through the end of the week with
morning lows in the upper 20s-lower 30s and and afternoon highs
in the mid 40s-lower 50s for the mountains. These cool temperatures
should slow the snowmelt into the streams and tributaries of the
Upper North Platte and Laramie rivers. A low pressure system will
be moving across the central Rockies Thursday and Friday, with the
potential for widespread precipitation on the order of a quarter
to half inch. Locally higher amounts will be possible with
thunderstorms. The southeast Wyoming mountains may receive one to
three inches of snow, especially above 9000 feet. Will continue to
monitor the impacts of rain on snow on area rivers, creeks and streams
this weekend.

&&

.CYS Watches/Warnings/Advisories...

WY...None.
NE...None.

&&

$$

UPDATE...GCC
SHORT TERM...REC
LONG TERM...MAJ
AVIATION...SML
FIRE WEATHER...REC
HYDROLOGY...MAJ



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000
FXUS65 KRIW 250501
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1100 PM MDT TUE MAY 24 2016

.Short Term...Tonight Through Wednesday

A major long wave low pressure trough extending from the eastern
Pacific off of the west coast to the eastern great plains will
remain over the region. This will keep cool air over the region
with southwest flow bringing Pacific moisture north along with
instability and jet dynamics supporting shower activity with
embedded afternoon and evening thunderstorms. Thunderstorms will
have small hail...heavy rain and strong wind gusts. Gusty
southwest winds will extend across the lower elevations of the
Red Desert...Wind River and Bighorn basins and Fremont...Natrona
and Johnson counties. Night time freezing to near freezing
temperatures in the mountains will retard the snowmelt. The snow
level will continue to fluctuate between 9000 feet and 7500 feet
day to night. Above 9000 feet accumulations of 2 to 4 inches a
day is expected. Some accumulation may occur below 9000 feet down
to around 8000 feet. Showers and thunderstorms will produce daily
precipitation from .25 to .5 of an inch with local 1 inch amounts.

.Long Term...Wednesday Night Through Tuesday

A major long wave low pressure trough extending from the eastern
Pacific off of the west coast to the eastern great plains will
remain over the region Wednesday night trough Tuesday. This will
keep cool air over the region with southwest flow bringing Pacific
moisture north along with instability and jet dynamics supporting
shower activity with embedded afternoon and evening thunderstorms.
Thunderstorms will have small hail...heavy rain and strong wind
gusts. Gusty southwest winds will extend across the lower
elevations of the Red Desert...Wind River and Bighorn basins and
Fremont...Natrona and Johnson counties. Night time freezing to
near freezing temperatures in the mountains will retard the
snowmelt. The snow level will continue to fluctuate between 9000
feet and 7500 feet day to night. Above 9000 feet accumulations of
2 to 4 inches a day is expected through the week. Some
accumulation may occur below 9000 feet down to around 8000 feet.
Showers and thunderstorms will produce daily precipitation from
.25 to .5 of an inch with local 1 inch amounts. The extended
models start to diverge over the weekend and spread apart more
Monday and Tuesday with speed...strength and location of short
wave low pressure troughs.

&&

.AVIATION.../06Z ISSUANCE/

West of the Continental Divide...KJAC/KRKS/KPNA/KBPI Routes

VFR conditions to prevail at the terminal sites except across the
far west...excluding KJAC which will see continuing vcnty -SHRA or
prevailing -SHRA and MVFR/occasional IFR conditions from now through
most of the forecast period. As one upper level disturbance moves
quickly and exits northern/northeastern Wyoming this morning,
another disturbance will keep isolated to scattered showers across
west and northwest Wyoming through the morning hours with frequent
mountain obscuration. Early morning low stratus and MVFR ceilings
or VCFG return to some terminals after 09z. Otherwise, showers and
isolated thunder will return to the rest of the region by mid to
late morning...lasting through the rest of the day before finally
decreasing in coverage by Wednesday evening. Brief periods of MVFR
cigs may be experienced with any heavier shower or storm.


East of the Continental Divide...KCPR/KCOD/KRIW/KWRL/KLND Routes

VFR conditions to prevail through the forecast period. The strong
upper level disturbance that brought showers and thunderstorms to
the region Tuesday, will move out of northern Wyoming this
morning...with showers ending across most of the area.
Showers and isolated thunder will again be possible by mid to late
morning near KCOD, then by early afternoon elsewhere. These showers
and storms may last into the mid evening period before decreasing in
coverage. Brief periods of MVFR cigs may be experienced with any
heavier shower or storm.

&&

.FIRE WEATHER...

A major long wave low pressure trough extending from the eastern
Pacific off of the west coast to the eastern great plains will
remain over the region into the weekend.  This will keep cool air
over the region with southwest flow bringing Pacific moisture north
along with instability and jet dynamics supporting shower activity
with embedded afternoon and evening thunderstorms. Thunderstorms
will have small hail...heavy rain and strong wind gusts. Over
the mountains...relative humidity will be elevated with lower
relative humidity and gusty southwest winds across the lower
elevations of the Red Desert...Wind River and Bighorn basins and
Fremont...Natrona and Johnson counties. Night time freezing to
near freezing temperatures in the mountains will retard the
snowmelt. The snow level will continue to fluctuate between 9000
feet and 7500 feet day to night. Above 9000 feet accumulations of
2 to 4 inches a day is expected through the week. Some
accumulation may occur below 9000 feet down to around 8000 feet.
Showers and thunderstorms will produce daily precipitation from
.25 to .5 of an inch with local 1 inch amounts. Outside of areas
of precipitation...mixing heights should rise high enough for good
to very good smoke dispersal in the afternoons.

&&

.RIW Watches/Warnings/Advisories...
None.
&&

$$

SHORT TERM...C.Baker
LONG TERM...C.Baker
AVIATION...Braun
FIRE WEATHER...C.Baker




000
FXUS65 KCYS 250005
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
605 PM MDT TUE MAY 24 2016

.UPDATE...
Issued at 1006 AM MDT Tue May 24 2016

Ongoing forecast looks to be in good shape. did pull severe
thunderstorm wording back west a little bit more to include
Cheyenne. Current SPC Mesoanalyst page showing a slight cap still
right along the east slopes of the Laramie Range that breaks
around 17Z. Latest EMCWRF shows convection beginning shortly after
that time. Could be looking at severe thunderstorms initiating
around 20-21Z along the I-25 corridor (Chugwater) with storms
congealing into a possible squall line late afternoon into the
central and northern Panhandle towards 00Z.

&&

.SHORT TERM...(Today through Thursday)
Issued at 145 AM MDT Tue May 24 2016

The main concern with this portion of the forecast is where the
convection will initiate today and where the best chance of severe
storms will be.

Today-Tonight:
Latest water vapor loop continues to show 60 to 70 kt of jet energy
moving out of the southwest with broad scale upper level diffluence
developing over the Rockies. It appears the leading edge of the
potential vorticity anomaly (pva) is in Northern Utah. The main
challenge for today will be where this pva ends up this afternoon
and where the convection will initiate. Latest NAM solution is
showing this anomaly affecting the northern Laramie Range early
this afternoon. Interestingly enough the experimental HRRR/local
WRF solutions are showing the initial development of the
convection this afternoon taking place in the northern Laramie
Range as well around 18-19z. If this ends up panning out, then we
may have an early threat for strong to severe storms further north
around Lusk and the Northern Panhandle. However, I am not as
confident that the low level moisture will get that far north with
these storms possibly having higher bases. However, the low level
shear (0-1km) is around 20 to 25kts at Chadron near a boundary
which may favor some brief high based tornados. However, the main
threat still appears to be large hail and damaging wind.

Further south, it is a matter of timing of when the second piece
of pva moves into northern Colorado and southern Wyoming. The
local WRF/HRRR are both showing convection developing by 21z.
These storms will certainly have more moisture to work with which
will tend to favor lower cloud bases especially in the southern
Panhandle. Effective bulk shear values will generally range from 45
to 50 kt, which will also favor rotating updrafts. A couple of
these storms may also have a threat of becoming supercellular with
even a possible brief tornado.

Most of this convection should move northeast at 30 to 35 mph, but
the right moving supercells will generally move east at 30-40 mph.

All of this convection may merge into a broken squall line between
00z-03z, but most of it should exit the forecast area by around
03z.

Tuesday night-Thursday:
We are a bit worried about some gusty winds following the line of
convection this evening. Models are showing good downward vertical
motion which may allow for some good mixing before sunset. Beyond
Tuesday night more upper level energy is progged to dive southeast
from Montana on Wednesday. Ahead of this upper level energy we will
see good downslope flow which will favor rather mild temperatures
before the next wave moves through the Rockies on Thursday and
brings cooler and wetter conditions.

.LONG TERM...(Thursday night through Monday)
Issued at 330 AM MDT Tue May 24 2016

The medium range models have been consistent with the timing and
track of the upper low affecting the central Rockies and plains
Thursday night and Friday. This system will widespread showers and
thunderstorms, with snow showers as snow levels drop to 9000 feet.
Refer to the Hydrology section for details on precipitation amounts.
It will be cooler than normal with highs in the 60s to near 70,
with 40s and 50s for the high country.

Precipitation coverage decreases somewhat this weekend and early
next week as a short wave ridge develops along the Front Range
ahead of the next upper trough moving into the Northwest CONUS.
The best chances for convection will focus over the higher terrain,
with more isolated coverage across the plains. The southwest flow
aloft between a upper ridge over the central CONUS and upper trough
axis to over the Northwest CONUS will allow temperatures to warm
to seasonal normals with highs in the mid 60s-mid 70s, and mid
50s-mid 60s for the high country.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 553 PM MDT Tue May 24 2016

The main concern this evening is the line of convection moving
through the KSNY taf site. This convection has maintained its
strength during the last couple of hours, but has remained below
severe limits. May see some gusty winds up to 35kts with small
hail in this cluster of storms. This cluster of storms may affect
the KAIA taf site as well during the next couple of hours as well,
but should not be as impactful as KSNY. The other cluster of
storms just west of KCDR may affect that taf site as well during
the next couple of hours. Could see some small hail and gusty
winds to 30 to 40 mph with this cluster as well. After this
cluster of convection exits the area...clearing skies are expected
during the remainder of the evening with gusty west winds tomorrow
at speeds of 20 to 30 mph.

&&

.FIRE WEATHER...
Issued at 145 AM MDT Tue May 24 2016

Fire weather concerns will be minimal during the next several days
due to chances of precipitation through the period and mostly wet
fuels from greenup.

&&

.HYDROLOGY...
Issued at 300 AM MDT Tue May 24 2016

Cool temperatures will persist through the end of the week with
morning lows in the upper 20s-lower 30s and and afternoon highs
in the mid 40s-lower 50s for the mountains. These cool temperatures
should slow the snowmelt into the streams and tributaries of the
Upper North Platte and Laramie rivers. A low pressure system will
be moving across the central Rockies Thursday and Friday, with the
potential for widespread precipitation on the order of a quarter
to half inch. Locally higher amounts will be possible with
thunderstorms. The southeast Wyoming mountains may receive one to
three inches of snow, especially above 9000 feet. Will continue to
monitor the impacts of rain on snow on area rivers, creeks and streams
this weekend.

&&

.CYS Watches/Warnings/Advisories...
WY...None.
NE...None.
&&

$$

UPDATE...GCC
SHORT TERM...REC
LONG TERM...MAJ
AVIATION...REC
FIRE WEATHER...REC
HYDROLOGY...MAJ




000
FXUS63 KUNR 241722
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1122 AM MDT TUE MAY 24 2016

.SHORT TERM...(Today Through Wednesday Night)
Issued at 310 AM MDT Tue May 24 2016

Current surface map high pressure across Montana with weak trof
from northeast to southwest South Dakota. Mostly clear skies
across the forecast. Upper low continues to spin across southern
Saskatchewan with shortwave moving through eastern Dakotas.
Another upper low is located over California. Sunny skies and
rapid warmup in store for the area this morning, then becoming
very active this afternoon and evening. Short range models in very
good agreement with shortwave lifting through eastern Wyoming into
western South Dakota with strong lift enhanced by right entrance
region of jet streak across North Dakota. Convective allowing
models show widespread thunderstorms late this afternoon into the
evening hours. The biggest issue will be return of low level
moisture and amount of instability. Surface dewpoints currently in
the 30s to lower 40s across the forecast area. Latest RAP/NAM
bring some lower 50 dewpoints into southwest South Dakota this
afternoon, while HRRR maintains lower to mid 40 dewpoints. With
lack of stronger return flow until this afternoon, RAP/NAM may a
little on the high side. Either way, the best instability will be
along southern portions of forecast area. Sufficient shear for
supercells, especially from southern Black Hills/Southwest South
Dakota. Bulk of convection should move north and east of the
forecast area after midnight. Upper low shift into eastern Montana
on Wednesday. Steep mid level lapse rates with marginal Boundary
layer moisture will result in scattered showers/thunderstorms.

.LONG TERM...(Thursday Through Monday)
Issued at 310 AM MDT Tue May 24 2016

Persistent upper level troughing over the northwest
CONUS will keep active southwest flow across the Northern Plains
through the Memorial Day weekend. Periodic shortwave energy will
eject out of the trough, keeping a daily chance of showers and
thunderstorms in the forecast through the holiday weekend.
Temperatures will be near seasonal averages, with highs each day in
the mid 60s to upper 70s. Lows at night will be in the 40s to mid
50s.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1120 AM MDT Tue May 24 2016

Showers and thunderstorms will develop across the area this
afternoon into the evening. Some strong storms will be
possible...mainly near the Nebraska border. MVFR/IFR conditions
will be possible near any precipitation.

&&

.UNR Watches/Warnings/Advisories...
SD...None.
WY...None.
&&

$$

SHORT TERM...7
LONG TERM...15
AVIATION...13




000
FXUS65 KRIW 241629
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1029 AM MDT TUE MAY 24 2016

.Short Term...Tuesday through Thursday night

The active weather pattern looks to continue through much of the
workweek. All is quiet right now on the weather front. However, this
will not last long as a front and associated shortwave move into the
area. Showers and thunderstorms will break out in the west during
the late morning hours and then progress eastward through the
afternoon and into the evening. Out west, only run of the mill type
storms are expected. Some snow is also possible at the higher
elevations, but likely nothing of consequence. Things do get a bit
more interesting East of the Divide though.

The thunderstorms will wait a bit longer areas east of the divide
today, allowing for more instability to build up. Soundings are also
showing a decent amount of shear of the speed and directional
variety that could support tilted updrafts that could sustain the
storms. In addition, the left front quadrant of a jet streak could
enhance upper divergence a bit. This could spell some stronger
storms and possible a few severe. But there are some limiting
factors. Temperatures are not expected to be terribly warm, only
getting to around 70 in most locations. Also, the atmosphere is
starting off rather dry. There is some indication of moisture
recovery however as weak surface low pressure may wrap moisture back
from Natrona County westward into the Big Horn basin.
Nevertheless, a lot of thunderstorms look to be higher based. With
inverted V soundings there could be some downburst wind gusts and
the shear is sufficient for decent sized hail. The Storm Prediction
Center does have the area eastward from around a Cody to Casper line
in a marginal risk. This looks reasonable at this time. For now, we
will stick to the small hail and gusty wind wording. Should be time
to beef up the wording since any stronger thunderstorms would be
late this afternoon or evening. Some storms could go later in the
night with a boundary lingering in the area, mainly across the
north. Snow will still be possible in the mountains as well.

Wednesday and Thursday still look active as well. With a boundary
remaining in the area and low heights still around. There will be a
chance for mainly afternoon and evening showers and thunderstorms
each day. Most of each day should be rain free, but all areas will
have at least a chance. With more cloud cover and less jet support
stronger storms should be less of a threat however. Temperatures
will remain below normal for most areas as well. Like previous days,
the most coverage of showers will be in the western and northern
portions of the county warning area.

.LONG TERM...Friday through Tuesday

GFS and ECMWF models bring in a storm system into the Pacific NW
states for Friday. Best chance for storms will be the NW and in
the north with lesser coverage central and south.

On Saturday the system gets additional energy dropping into it
from Western Canada. This energy creates issues with the original
circulation as the storm system begins to elongate and change
orientation from Saturday night through Monday. The overall
pattern will be a SW flow aloft over the area all weekend into
next week. The flow is diffluent at times which may lead to
increased convection at times.

The models drive a cold front into western WY late afternoon
Saturday which may be the focus for some strong storms. The ECMWF
model pushes the cold front through the entire region Saturday
night leading to a cooler Sunday with isolated showers and
storms. Then the ECMWF model brings the other piece of energy
toward NW around 00z Mon and rotates it into Montana Monday while
driving another cold front into the area for Monday. Thus a chance
for showers and storms.

The GFS model has its own scenario on how this weather pattern
plays out. It has the initial cold front Saturday afternoon and
evening with the better storm coverage over NW and northern WY.
The big difference is that GFS does not have the second cold
frontal push Sunday night and Monday and thus much warmer temps
for Mon. Plus the GFS has isolated to scattered showers and
storms across the region Sun and Mon.

Bottom line forecast for Memorial Day weekend outdoor activity
plans...the threat for thunderstorms over and near the mountains
each day with strong wind gusts, hail, periods of heavy rain, and
frequent lightning from the stronger storms. The storm coverage
over the lower elevations will be less but the above threats are
still possible at times.

Next Tue looks like the usual afternoon and evening thunderstorm
chance with a frontal boundary draped across the state.

&&

.Aviation.../18Z issuance/

West of the Continental Divide...KJAC/KRKS/KPNA/KBPI Routes

A disturbance will move northeast across the region today bringing
scattered showers and isolated thunderstorms through this
evening...most numerous in the high country. Brief MVFR conditions
in lower ceilings will occur in and near heavier showers and storms.
Wind gusts of 35-45 kts are possible near stronger or higher based
storms. Most activity will decrease by 04z Wed...lingering a bit
longer near KJAC. Early morning low stratus and MVFR ceilings or
VCFG return to some terminals after 09z. Another round of light
showers will return to the southwest by morning.


East of the Continental Divide...KCPR/KCOD/KRIW/KWRL/KLND Routes

VFR conditions to prevail through the forecast period unless a
strong thunderstorm is encountered. A strong disturbance will move
across the region today bringing scattered showers and thunderstorms
east of the divide later this afternoon through the evening...with
periods of brief MVFR conditions in lower ceilings in and near
heavier showers and storms late this afternoon and evening. More
numerous and stronger thunderstorms are possible in both Natrona and
Johnson counties later this afternoon and evening with some storms
producing winds gusts in excess of 45 knots...hail from one half
inch to one inch...and brief heavy rain with frequent lightning.
This activity will decrease from south to north after 04z Wed. Early
morning low stratus and MVFR ceilings or VCFG returns to some
terminals after 09z.

&&

.FIRE WEATHER...

An upper level disturbance and cold front will move towards the area
today and bring a chance of mainly afternoon and evening showers and
thunderstorms with the most numerous storms in the west. A few
thunderstorms from the Big Horn Basin eastward could become strong
to possibly severe with strong and erratic wind gusts as well as
hail. A gusty southwest wind will develop across portions of
Sweetwater County and the Green and Rattlesnake Ranges. Cooler then
normal temperatures and the chance of mainly afternoon showers and
thunderstorms will linger through Thursday.

&&

.RIW Watches/Warnings/Advisories...None.

&&

$$

SHORT TERM...Hattings
LONG TERM...AR
AVIATION...PS
FIRE WEATHER...Hattings




000
FXUS65 KRIW 240942
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
342 AM MDT TUE MAY 24 2016

.Short Term...Tuesday through Thursday night

The active weather pattern looks to continue through much of the
workweek. All is quiet right now on the weather front. However, this
will not last long as a front and associated shortwave move into the
area. Showers and thunderstorms will break out in the west during
the late morning hours and then progress eastward through the
afternoon and into the evening. Out west, only run of the mill type
storms are expected. Some snow is also possible at the higher
elevations, but likely nothing of consequence. Things do get a bit
more interesting East of the Divide though.

The thunderstorms will wait a bit longer areas east of the divide
today, allowing for more instability to build up. Soundings are also
showing a decent amount of shear of the speed and directional
variety that could support tilted updrafts that could sustain the
storms. In addition, the left front quadrant of a jet streak could
enhance upper divergence a bit. This could spell some stronger
storms and possible a few severe. But there are some limiting
factors. Temperatures are not expected to be terribly warm, only
getting to around 70 in most locations. Also, the atmosphere is
starting off rather dry. There is some indication of moisture
recovery however as weak surface low pressure may wrap moisture back
from Natrona County westward into the Big Horn basin.
Nevertheless, a lot of thunderstorms look to be higher based. With
inverted V soundings there could be some downburst wind gusts and
the shear is sufficient for decent sized hail. The Storm Prediction
Center does have the area eastward from around a Cody to Casper line
in a marginal risk. This looks reasonable at this time. For now, we
will stick to the small hail and gusty wind wording. Should be time
to beef up the wording since any stronger thunderstorms would be
late this afternoon or evening. Some storms could go later in the
night with a boundary lingering in the area, mainly across the
north. Snow will still be possible in the mountains as well.

Wednesday and Thursday still look active as well. With a boundary
remaining in the area and low heights still around. There will be a
chance for mainly afternoon and evening showers and thunderstorms
each day. Most of each day should be rain free, but all areas will
have at least a chance. With more cloud cover and less jet support
stronger storms should be less of a threat however. Temperatures
will remain below normal for most areas as well. Like previous days,
the most coverage of showers will be in the western and northern
portions of the county warning area.

.LONG TERM...Friday through Tuesday

GFS and ECMWF models bring in a storm system into the Pacific NW
states for Friday. Best chance for storms will be the NW and in
the north with lesser coverage central and south.

On Saturday the system gets additional energy dropping into it
from Western Canada. This energy creates issues with the original
circulation as the storm system begins to elongate and change
orientation from Saturday night through Monday. The overall
pattern will be a SW flow aloft over the area all weekend into
next week. The flow is diffluent at times which may lead to
increased convection at times.

The models drive a cold front into western WY late afternoon
Saturday which may be the focus for some strong storms. The ECMWF
model pushes the cold front through the entire region Saturday
night leading to a cooler Sunday with isolated showers and
storms. Then the ECMWF model brings the other piece of energy
toward NW around 00z Mon and rotates it into Montana Monday while
driving another cold front into the area for Monday. Thus a chance
for showers and storms.

The GFS model has its own scenario on how this weather pattern
plays out. It has the initial cold front Saturday afternoon and
evening with the better storm coverage over NW and northern WY.
The big difference is that GFS does not have the second cold
frontal push Sunday night and Monday and thus much warmer temps
for Mon. Plus the GFS has isolated to scattered showers and
storms across the region Sun and Mon.

Bottom line forecast for Memorial Day weekend outdoor activity
plans...the threat for thunderstorms over and near the mountains
each day with strong wind gusts, hail, periods of heavy rain, and
frequent lightning from the stronger storms. The storm coverage
over the lower elevations will be less but the above threats are
still possible at times.

Next Tue looks like the usual afternoon and evening thunderstorm
chance with a frontal boundary draped across the state.

&&

.Aviation.../12Z issuance/

West of the Continental Divide...KJAC/KRKS/KPNA/KBPI Routes

VFR conditions to prevail through at least 09z. A strong
disturbance will move across the region today bringing scattered
showers and thunderstorms to most of the west this afternoon and
evening...with periods of brief MVFR conditions in lower ceilings in
and near heavier showers and storms. Stronger embedded storms will
produce gusty erratic winds to 35 knots with small hail and brief
heavy rain. Stronger gusts in excess of 45 knots will be possible
across Sweetwater county including KRKS. Most activity will
decrease by 04z Wed...lingering a bit longer near KJAC. Early
morning low stratus and MVFR ceilings or VCFG return to some
terminals after 09z.

East of the Continental Divide...KCPR/KCOD/KRIW/KWRL/KLND Routes

VFR conditions to prevail through the forecast period. A strong
disturbance will move across the region today bringing scattered
showers and thunderstorms east of the divide later this afternoon
through the evening...with periods of brief MVFR conditions in lower
ceilings in and near heavier showers and storms late this
afternoon and evening. More numerous and stronger thunderstorms
are possible in both Natrona and Johnson counties later this
afternoon and evening with some storms producing winds gusts in
excess of 45 knots...hail from one half inch to one inch...and
brief heavy rain with frequent lightning. This activity will
decrease from south to north after 04z Wed. Early morning low
stratus and MVFR ceilings or VCFG returns to some terminals after
09z.

&&

.FIRE WEATHER...

An upper level disturbance and cold front will move towards the area
today and bring a chance of mainly afternoon and evening showers and
thunderstorms with the most numerous storms in the west. A few
thunderstorms from the Big Horn Basin eastward could become strong
to possibly severe with strong and erratic wind gusts as well as
hail. A gusty southwest wind will develop across portions of
Sweetwater County and the Green and Rattlesnake Ranges. Cooler then
normal temperatures and the chance of mainly afternoon showers and
thunderstorms will linger through Thursday.

&&

.RIW Watches/Warnings/Advisories...None.

&&

$$

SHORT TERM...Hattings
LONG TERM...AR
AVIATION...Braun
FIRE WEATHER...Hattings




000
FXUS65 KRIW 240501
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1101 PM MDT MON MAY 23 2016

.Short Term...Tonight Through Thursday

Large upper low continues to spin over Southern Saskatchewan with
multiple disturbances rotating around it. Embedded weak wave is
slowly moving ne into Southwest Wyoming attm with some weak
showers/virga. Weak thermal trough and wraparound moisture is also
aiding in some weak showers over the northwest early this
afternoon. Limited instability today and not a lot of moisture to
work with. Tuesday we see a potential stronger shortwave moving up
from the southeast late in the day and then heading towards the
northeastern zones. At the same time, a weak front will drop down
into the northern zones tonight. Some potential jet support may
also come into play late in the afternoon or evening as nose of
srn jet moves into Southeastern Wyoming and right entrance region
of northern jet streak is nearby. How much moisture is able to
move in from the southeast is still in question as is when will it
arrive if it does. It looks like it will be early evening before
any better moisture arrives so we`ll just have to watch how the
shortwave/upper forcing timing is and how our return flow moisture
is to see how strong some of these storms may be in mainly Johnson
County. SPC has ern Johnson in marginal risk and that looks good
for now. Multiple ripples in the southwest flow appear to be in
play Tuesday night and Wednesday to keep a chance of showers and
isold storms across the area, especially in the west and north
where the front may remain. Unsettled weather remains through
Thursday with northern low passing into the ND and a southern
upper low moving across the 4-corners region. Weak frontal
boundary east of the divide may be a focus for afternoon
convection as plenty of mid level moisture will remain with a
little more low level available behind the front.

.Long Term...Thursday Night Through Monday

Interesting extended period as once again we have a Memorial Day
upper low to contend with. This system is currently in the Alaska
region and will drop down into the WA/Nrn ID area on Friday and
then dig into the Inter-mountain west for the remainder of the
Memorial Day weekend as the large scale pattern shows a mean
trough holding over the west through the period. The GFS is
showing the frontal boundary holding across at least the north
half through much of this period with potential overrunning aloft
to increase pcpn chances east of the divide Friday onward. The new
Euro is more progressive with the low swinging it across on
Saturday night already. Not really buying into this idea with mean
trough holding over the west. If that happens, then there will be
likely another low quickly replacing it over the west. Will
continue continuity with an upper low over the west much of the
weekend with cool to cold in YNP, cooler north than south along
with higher pops west and north.

&&

.AVIATION.../06Z ISSUANCE/

West of the Continental Divide...KJAC/KRKS/KPNA/KBPI Routes

VFR conditions to prevail through the forecast period. A strong
disturbance will move across the region today bringing scattered
showers and thunderstorms to most of the west this afternoon and
evening...with periods of brief MVFR conditions in lower cigs in and
near heavier showers and storms. Stronger embedded storms will
produce gusty erratic winds to 35 kts with small hail and brief
heavy rain. Stronger gusts in excess of 45 kts will be possible
across Sweetwater county including KRKS. This activity will decrease
by 04z Wed.

East of the Continental Divide...KCPR/KCOD/KRIW/KWRL/KLND Routes

VFR conditions to prevail through the forecast period. A strong
disturbance will move across the region today bringing scattered
showers and thunderstorms east of the divide later this afternoon
through the evening...with periods of brief MVFR conditions in lower
cigs in and near heavier showers and storms late this afternoon and
evening. More numerous and stronger thunderstorms are possible in
both Natrona and Johnson counties later this afternoon and evening
with some storms producing winds gusts in excess of 45 kts...hail
from one half inch to one inch...and brief heavy rain with frequent
lightning. This activity will decrease from south to north after 03z
Wed.

&&

.FIRE WEATHER...

Isolated to widely scattered showers and a few thunderstorms will
be possible into the evening hours. A gusty breeze will continue
across portions of the area, but high winds are not anticipated.
Relative humidity should remain above critical levels. An upper
level disturbance will approach on Tuesday and bring an increased
chance of afternoon showers and thunderstorms. A weak cold front
will move into the north tonight with a northerly wind setting the
stage for lower mixing heights on Tuesday while the south remains
well mixed.

&&

.RIW Watches/Warnings/Advisories...None.

&&

$$

SHORT TERM...PS
LONG TERM...PS
AVIATION...Braun
FIRE WEATHER...PS




000
FXUS65 KCYS 232332
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
533 PM MDT MON MAY 23 2016

.SHORT TERM...(Tonight - Wednesday)
Issued at 300 PM MDT Mon May 23 2016

Showers and thunderstorms should develop shortly as recent visible
satellite imagery shows widespread cumulus along the I-80 corridor
between Rawlins and Cheyenne. No severe weather expected late this
afternoon or evening with weak instability; however, an inverted-v
appearance to forecast soundings and high cloud bases suggests the
potential for gusty winds especially with decaying storms. Hail is
also possible with more robust cores. Focus for convection through
the evening hours should be in the vicinity of a Pine Bluffs WY to
Alliance NE line, closer to the H25 speed max and the llvl theta-e
ridge axis. The HRRR has been rather consistent with tstm coverage
in this area later today, so opted to include likely PoPs into the
early evening. Expect convection to diminish quickly with the loss
of daytime heating.

Severe thunderstorms are looking more likely for Tuesday afternoon
with excellent instability/shear and the presence of significantly
better forcing than what we had on Saturday. The 1730z installment
of the SPC Day 2 outlook nudged the Enhanced Risk farther westward
into Kimball, so this could be a higher-end setup for the cwa. The
models are in good agreement with a vigorous/fast-moving mid-level
shortwave lifting across the southern Laramie Range and eventually
across the high plains after 18z, likely originating from a parent
upper trough currently off the CA coast. This will promote surface
cyclogenesis over northeast CO and moist/southeast upslope flow in
the low-levels. The timing of the lead impulse and backing of flow
near the surface suggests convective initiation in the vicinity of
the Laramie Range around 18z, quickly spreading onto the plains as
cinh rapidly weakens. Likely PoPs have been introduced along and e
of the surface dryline. BUFKIT soundings suggest MUCAPES over 3000
J/kg over the southern NE Panhandle and around 1000 J/kg near KCYS
around 21z. 45-50kt 0-6 km shear vectors oriented perpendicular to
the dryline suggests potential for discrete supercells potentially
capable of very large hail, and maybe a couple of tornadoes w/good
directional shear in the effective layer. Thinking that high cloud
bases may mitigate the tornado threat, but still expect widespread
severe storms. Expanded T+ wording westward into Cheyenne as model
guidance usually tries to mix the dryline east too quickly. Threat
for convection should be east of the CWA by 03z Wed.

An unsettled pattern will continue into Weds with active southwest
flow in place in the mid and upper-levels. Widely scattered shower
and thunderstorm activity can be expected once again, although the
threat for severe weather should be low.

.LONG TERM...(Wednesday night - Monday)
Issued at 300 PM MDT Mon May 23 2016

Cool and unsettled weather will continue in the long term with
almost daily chances for afternoon and evening showers and
thunderstorms. A low pressure system continues to track across
Colorado Thursday and Friday that could bring substantial rainfall
to the area. Right now though...its looking like the mountains
will see overnight snow above 9K feet Thursday and Friday with
rain during the day.

Cool and unsettled weather to continue into the weekend. No major
warm ups expected.

&&

.AVIATION...(For the 00Z TAFS through Tuesday afternoon)

Area of thunderstorms which developed over SE Wyoming have moved
into southern Nebraska this evening. These showers and Tstorms will
linger until 02z and then dissipate or slide to the east into
central Nebraska. Kept mention of VCTS and gusty convective winds
over the next few hours...and then clearing skies overnight with
light and variable winds.  Another round of thunderstorms is
expected Tuesday afternoon. These thunderstorms may be stronger and
include large hail and strong winds through Tuesday evening...mainly
east of the Laramie Range.

&&

.FIRE WEATHER...
Issued at 300 PM MDT Mon May 23 2016

No major fire weather concerns over the next several days with rhs
well outside of critical thresholds. Daily chances for showers and
thunderstorms will exist through the week. Thunderstorms should be
quite numerous on Tuesday afternoon and evening, mainly along/east
of the Laramie Range. Some storms will be severe, with very large/
destructive hail and damaging winds.

&&

.HYDROLOGY...
Issued at 110 PM MDT Mon May 23 2016

Cool temperatures continuing through the week with morning lows at
or below freezing and afternoon highs in the mid 40s to near 50
for the mountains. This should slow the snow melt into streams and
tributaries of the Upper North Platte and Laramie Rivers. Need to
be watching Thursday and Friday though as a low pressure system
tracks across Colorado. Latest forecast guidance does show fairly
widespread precip in the Snowy and Sierra Madre Ranges. Need to be
watching how this rain on snow event will impact river levels
going into the weekend.

&&

.CYS Watches/Warnings/Advisories...
WY...None.
NE...None.
&&

$$

SHORT TERM...CLH
LONG TERM...GCC
AVIATION...GCC
FIRE WEATHER...CLH
HYDROLOGY...GCC




000
FXUS63 KUNR 232307
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
507 PM MDT MON MAY 23 2016

.SHORT TERM...(This Evening Through Tuesday Night)
Issued at 211 PM MDT Mon May 23 2016

Water vapor shows nearly stationary low over srn SASK with fairly
dry sw flow extending into the nrn plains. A notable short wave is
ejecting newd through far nrn CO with a few -tsra already forming
over far sern WY. At the sfc...weak low is located over far nwrn
WY.

Tonight...a few -tsra are possible given the short wave ejecting
newd...but given minimal moisture and instability overall coverage
will be limited to mainly higher terrain as well as nwrn SD in
closer proximity to the sfc low.

Tuesday...slightly warmer temps are expected. Dry conditions
expected in the morning...but a more substantial negatively
tilted short wave will eject newd towards the cwfa by later in the
aftn. MLCAPE expected to rise into the 1000-2000J/KG range along
with ample shear for some strong to severe storms...with the best
convective parameters generally along/South of I-90. Best
concentration of storms will likely be in the BLKHLS as well as
southwest through south central SD. Precipitable waters in the
125-175% of normal range from southwest through south central SD
could result in heavier rains for that area. Storms will end from
southwest to northeast by late evening.

.LONG TERM...(Wednesday Through Monday)
Issued at 211 PM MDT Mon May 23 2016

Persistent upper level troughing over the northwest
CONUS will keep active southwest flow across the Northern Plains
through the Memorial Day weekend. Periodic shortwave energy will
eject out of the trough, keeping a daily chance of showers and
thunderstorms in the forecast through the holiday weekend.
Temperatures will be near seasonal averages, with highs each day in
the mid 60s to upper 70s. Lows at night will be in the 40s to lower
50s.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Tuesday Evening)
Issued At 505 PM MDT Mon May 23 2016

An isolated shower or thunderstorm will be possible
across far northwest South Dakota this evening. Otherwise VFR
conditions are expected through Tuesday morning. The next system
will bring sct shra and ts to much of the region tues aft and eve.

&&

.UNR Watches/Warnings/Advisories...
SD...None.
WY...None.
&&

$$

SHORT TERM...Johnson
LONG TERM...MLS
AVIATION...JC




000
FXUS65 KRIW 231949
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
149 PM MDT MON MAY 23 2016

.Short Term...Tonight Through Thursday

Large upper low continues to spin over Southern Saskatchewan with
multiple disturbances rotating around it. Embedded weak wave is
slowly moving ne into Southwest Wyoming attm with some weak
showers/virga. Weak thermal trough and wraparound moisture is also
aiding in some weak showers over the northwest early this
afternoon. Limited instability today and not a lot of moisture to
work with. Tuesday we see a potential stronger shortwave moving up
from the southeast late in the day and then heading towards the
northeastern zones. At the same time, a weak front will drop down
into the northern zones tonight. Some potential jet support may
also come into play late in the afternoon or evening as nose of
srn jet moves into Southeastern Wyoming and right entrance region
of northern jet streak is nearby. How much moisture is able to
move in from the southeast is still in question as is when will it
arrive if it does. It looks like it will be early evening before
any better moisture arrives so we`ll just have to watch how the
shortwave/upper forcing timing is and how our return flow moisture
is to see how strong some of these storms may be in mainly Johnson
County. SPC has ern Johnson in marginal risk and that looks good
for now. Multiple ripples in the southwest flow appear to be in
play Tuesday night and Wednesday to keep a chance of showers and
isold storms across the area, especially in the west and north
where the front may remain. Unsettled weather remains through
Thursday with northern low passing into the ND and a southern
upper low moving across the 4-corners region. Weak frontal
boundary east of the divide may be a focus for afternoon
convection as plenty of mid level moisture will remain with a
little more low level available behind the front.

.Long Term...Thursday Night Through Monday

Interesting extended period as once again we have a Memorial Day
upper low to contend with. This system is currently in the Alaska
region and will drop down into the WA/Nrn ID area on Friday and
then dig into the Inter-mountain west for the remainder of the
Memorial Day weekend as the large scale pattern shows a mean
trough holding over the west through the period. The GFS is
showing the frontal boundary holding across at least the north
half through much of this period with potential overrunning aloft
to increase pcpn chances east of the divide Friday onward. The new
Euro is more progressive with the low swinging it across on
Saturday night already. Not really buying into this idea with mean
trough holding over the west. If that happens, then there will be
likely another low quickly replacing it over the west. Will
continue continuity with an upper low over the west much of the
weekend with cool to cold in YNP, cooler north than south along
with higher pops west and north.

&&

.AVIATION.../00Z ISSUANCE/

West of the Continental Divide...KJAC/KRKS/KPNA/KBPI Routes

Isolated to widely scattered showers and a few thunderstorms will
continue through about 03z before ending or retreating to the
higher peaks. Brief mountain obscuration will occur near any
storms. Strong wind gusts are possible near any of these
showers/thunderstorms into this evening. Another stronger
disturbance will approach on Tuesday bringing scattered showers
and thunderstorms to most of the west Tuesday afternoon and
evening.

East of the Continental Divide...KCPR/KCOD/KRIW/KWRL/KLND Routes

Gusty southwest wind of 15 to 30 mph will continue in many areas
east of the divide into this evening with stronger gusts near any
isolated showers or thunderstorms. Another stronger disturbance
will approach on Tuesday bringing isolated to widely scattered
showers and thunderstorms to the area in the afternoon and
evening. More numerous and stronger thunderstorms are possible in
Johnson County later Tuesday afternoon and evening but everyone
has at least a chance of isolated thunderstorms with strong wind
and small hail.

&&

.FIRE WEATHER...

Isolated to widely scattered showers and a few thunderstorms will
be possible into the evening hours. A gusty breeze will continue
across portions of the area, but high winds are not anticipated.
Relative humidity should remain above critical levels. An upper
level disturbance will approach on Tuesday and bring an increased
chance of afternoon showers and thunderstorms. A weak cold front
will move into the north tonight with a northerly wind setting the
stage for lower mixing heights on Tuesday while the south remains
well mixed.

&&

.RIW Watches/Warnings/Advisories...None.

&&

$$

SHORT TERM...PS
LONG TERM...PS
AVIATION...PS
FIRE WEATHER...PS




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