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000
FXUS65 KPSR 301111
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
411 AM MST MON MAY 30 2016

.UPDATE...Updated aviation discussion.

&&

.SYNOPSIS...
A slow-moving low pressure system across the desert southwest will
persist through Tuesday yielding cooler than normal temperatures and
mostly dry conditions. Thereafter high pressure builds over the
regions for a sharp warming trend. By the weekend, many lower desert
locations will reach the 110 degree mark.

&&

.DISCUSSION...
Today through Wednesday...
A weak upper low is centered over the Mohave Desert early this
morning. To the north is an upper trough centered with an axis over
the northern Rockies. In between the low and the trough is a
deformation zone. Upstream of our low is a ridge just offshore.
Satellite imagery shows indications of outflows and gravity waves
pushing westward to the Continental Divide due to convection over the
Plains (especially northern Texas). As the low slowly drifts east-
southeastward, it will try to tap into moisture from the Plains as
well as subtropical moisture from Baja and Sonora. Being that it is
weak, the moist advection will be meager. However, both hi-res and
larger scale models depict convection developing over northern AZ
today with more coverage Tuesday. With the low center dipping south
of the Mexico border by Tuesday afternoon, northeasterly steering
flow will help move storms from the Rim and Yavapai County into
south-central AZ. This would primarily affect southern Gila and
northern Maricopa Counties. The nature of the convection will be
high based and shallow given the very modest moisture availability.
Thus, no real precip opportunity but rather there will be gusty wind
potential and thus blowing dust potential. Our local WRF-NMM is the
most aggressive with the coverage and even has La Paz County and
Pima County getting into the mix. Other models (including NCEP WRFs
and UofA WRFs) are not as optimistic. Held on to the patchy blowing
dust in the grids for late Tuesday afternoon and evening but pared
back the area. By Wednesday afternoon, the low will be centered over
the Sonora/Chihuahua border. With lingering moisture and
northeasterly steering flow, added mention of slight chance t-storms
for our higher terrain zone northeast and east of metro Phoenix for
Wed. aft/eve.

As for temperatures, they will be a little bit below normal today and
near normal Tuesday (slightly above near and west of the Lower
Colorado River Valley). There will be additional warming Wednesday as
the low exits and the ridge advances inland. That will be the first
day of this week for 100 degree mark over the Phoenix area.

Thursday through Sunday...
The short story is that a strong ridge keeps building inland with
500mb heights in the 592-594dm range Friday and Saturday. NAEFS
depicts 850mb temps reaching and exceeding the 90th percentile both
of those days (especially Saturday). This pattern will result in well
above normal temperatures (even for early June) with most lower
deserts reaching the 110 degree mark Friday and Saturday. One minor caveat
is a backdoor front pushing against the Continental Divide late in
the week which could conceivably keep temps over south-central AZ
slightly below forecast but probably would only be felt over the
higher terrain - if at all. The ridge starts shifting eastward Sunday
in response to an advancing low pressure system leading to slight
cooling (more noticeably for southeast CA).

&&

.AVIATION...
South-Central Arizona Including KPHX, KIWA, and KSDL...

A weak low pressure system will move into Arizona today, though no
direct aviation weather impacts are anticipated through Tuesday
morning. Winds will generally remain less than 10 kt and follow
typical upslope/downslope patterns across the Phoenix area.

Southeast California/Southwest Arizona Including KIPL and KBLH...

Lighter than normal winds are expected through Tuesday. At KIPL,
directions will vary while at KBLH, winds will generally retain a
southerly or easterly component.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Wednesday through Sunday...
A strong high pressure system is forecast to build into the region
providing some of the warmest afternoon temperatures of the year by
the weekend. Afternoon temperatures will be 5 to 8 degrees above
normal. Typical afternoon and evening southwest winds 10 to 15 mph
are expected each day. Good recovery is expected at night. Minimum
relative humidities are generally expected in the 8 to 12 percent
range.

&&

.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

Visit us on Facebook...Twitter...and at weather.gov/phoenix

DISCUSSION...AJ
AVIATION...Hirsch
FIRE WEATHER...Vasquez





000
FXUS65 KPSR 281203
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
503 AM MST SAT MAY 28 2016

.UPDATE...
UPDATED AVIATION AND FIRE WEATHER SECTIONS.

&&

.SYNOPSIS...
A broad area of low pressure will persist over the western United
States through the beginning of next week yielding somewhat cooler
than normal temperatures and dry conditions. Strengthening high
pressure much of next week will bring a warming trend with high
temperatures in the lower deserts pushing near 100 degrees by the
middle of the week. A stretch of well-above normal temperatures is
likely later in the week.

&&

.DISCUSSION...
Dry westerly flow predominates across the desert southwest this
morning. Further upstream, latest streamline analysis indicates the
presence of a weak trough off of the CA coast. Continued increase in
thicknesses is expected today ahead of the trough which will equate
to temperature rises generally between 4 and 6 degrees across south-
central AZ. Despite the warming trend, temperatures will still fall
in the below-normal category.

Operational models remain in good agreement through the short-term,
indicating that the aforementioned mid-level trough will briefly
close off Sunday while moving into southern CA. This system is
moisture-starved and its main impact will be on temperatures, which
will be a degree or two cooler on Sunday. The trough will weaken
slightly Monday while continuing to slide eastward into AZ. An
additional degree of cooling is likely across AZ, however much warmer
conditions are expected across CA as a ridge in the eastern Pacific
moves eastward towards the west coast.

Residual moisture in the wake of the compact low pressure system
should be sufficient for isolated showers and thunderstorms
Tuesday/Wednesday. However, latest hi-res guidance suggests that the
activity will mainly be relegated to the higher terrain north and
east of Phoenix. Pops generally remain less than 5 percent in these
areas.

Latest guidance continues to indicate that the ridge will build
across the western CONUS, yielding steady height rises and a
continued warming trend during the mid to late week period. Temperatures
were increased for Thursday and Friday and generally represent the
70th percentile of all available guidance, which is well short of
records. Looking ahead to next weekend, operational GFS and ECMWF
diverge markedly, with the GFS depicting an eastern Pacific trough
fracturing and moving into the intermountain west. This solution is
not supported by other ensemble members and was dismissed, with the
expectation that the dry conditions and above normal temperatures
will persist.

&&

.AVIATION...
South-Central Arizona Including KPHX, KIWA, and KSDL and
Southeast California/Southwest Arizona Including KIPL and KBLH

A weak upper low near the California coast will lead to strengthening
southerly flow in the lower levels of the troposphere. Over south-
central AZ as mixing develops this morning, surface winds will hold
on to a predominantly southerly component through at least 21Z before
slowly trending to westerly by late afternoon. Expect gusts to be
well below 20kts. Southerly winds will be stronger over southwest AZ
and southeast CA (most noticeably over the Lower Colorado River
Valley with gusts of 15-20kts). Otherwise, clear skies except perhaps
for some very minor cirrus.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
Monday through Friday...
A weak upper low will keep temperatures near normal on Monday. A
ridge of high pressure then begins moving into the Desert Southwest
on Tuesday for the beginning of a warming trend. Expect most lower
elevations to reach 100 by Wednesday. Additional warming will make
for well above normal temperatures by Friday. Minimum humidities
will be in the 10-15% range on the lower elevations (dipping to
single digits east of the Lower Colorado River Valley by Friday).
Overnight recovery will be fair to good. No strong wind events are
expected. Anticipate Wednesday to have the strongest afternoon
breezes and Thursday the lightest. Otherwise, familiar warm season
wind patterns can be expected.


&&

.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

Visit us on Facebook...Twitter...and at weather.gov/phoenix

DISCUSSION...Hirsch
AVIATION...AJ
FIRE WEATHER...AJ





000
FXUS65 KPSR 281036
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
336 AM MST SAT MAY 28 2016

.SYNOPSIS...
A broad area of low pressure will persist over the western United
States through the beginning of next week yielding somewhat cooler
than normal temperatures and dry conditions. Strengthening high
pressure much of next week will bring a warming trend with high
temperatures in the lower deserts pushing near 100 degrees by the
middle of the week. A stretch of well-above normal temperatures is
likely later in the week.

&&

.DISCUSSION...
Dry westerly flow predominates across the desert southwest this
morning. Further upstream, latest streamline analysis indicates the
presence of a weak trough off of the CA coast. Continued increase in
thicknesses is expected today ahead of the trough which will equate
to temperature rises generally between 4 and 6 degrees across south-
central AZ. Despite the warming trend, temperatures will still fall
in the below-normal category.

Operational models remain in good agreement through the short-term,
indicating that the aforementioned mid-level trough will briefly
close off Sunday while moving into southern CA. This system is
moisture-starved and its main impact will be on temperatures, which
will be a degree or two cooler on Sunday. The trough will weaken
slightly Monday while continuing to slide eastward into AZ. An
additional degree of cooling is likely across AZ, however much warmer
conditions are expected across CA as a ridge in the eastern Pacific
moves eastward towards the west coast.

Residual moisture in the wake of the compact low pressure system
should be sufficient for isolated showers and thunderstorms
Tuesday/Wednesday. However, latest hi-res guidance suggests that the
activity will mainly be relegated to the higher terrain north and
east of Phoenix. Pops generally remain less than 5 percent in these
areas.

Latest guidance continues to indicate that the ridge will build
across the western CONUS, yielding steady height rises and a
continued warming trend during the mid to late week period. Temperatures
were increased for Thursday and Friday and generally represent the
70th percentile of all available guidance, which is well short of
records. Looking ahead to next weekend, operational GFS and ECMWF
diverge markedly, with the GFS depicting an eastern Pacific trough
fracturing and moving into the intermountain west. This solution is
not supported by other ensemble members and was dismissed, with the
expectation that the dry conditions and above normal temperatures
will persist.

&&

.AVIATION...
South-Central Arizona Including KPHX, KIWA, and KSDL and
Southeast California/Southwest Arizona Including KIPL and KBLH

Clear skies to persist through Saturday under a light wind regime.
May have some occasional gusts during the afternoon hours Saturday,
but less than 20 kts. Wind directions for the Phoenix terminals will
follow typical diurnal tendencies and generally follow a southerly
component for KIPL and KBLH. No aviation impacts through the period.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
Monday through Friday...
A hot and dry weather pattern will dominate the week including a
strong high pressure ridge that will build over the region from
Wednesday through Friday. Hot and near normal daytime high
temperatures reaching as high as the lower triple digits through
Wednesday are expected to increase to 100 to 106 degrees beginning
Thursday. In addition, minimum relative humidities of 8 to 15
percent will dry to the 7 to 11 percent range by Friday.
Breezy southerly to southwesterly winds with gusts of 15 to 20 mph
are forecast for Wednesday afternoon and evening.

&&

.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

Visit us on Facebook...Twitter...and at weather.gov/phoenix

DISCUSSION...Hirsch
AVIATION...Kuhlman
FIRE WEATHER...Sawtelle





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