Home > Products > Valid Products > AFD

000
FXUS66 KSEW 242141
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
240 PM PDT TUE MAY 24 2016

.SYNOPSIS...Clouds might break up a bit late this afternoon and evening
but then they will fill back in overnight into Wednesday. An upper low
will bring an increasing chance of showers Thursday through Saturday.
Another upper level trough will reach the area Sunday night or Monday.

&&

.SHORT TERM...After some sunbreaks later this afternoon and evening
the clouds will fill back in overnight. Onshore flow will increase
Wednesday in response to an upper level low digging south along the
British Columbia coast. The increasing onshore flow will limit the
amount of afternoon sunshine on Wednesday and give slightly cooler
max temps. As the upper level low sags south Thursday and Friday
there will be an increasing chance of showers with stronger onshore
flow.

.LONG TERM...The 12z gfs takes the center of the low from the
central B.C. coast on Thursday and drops it SE into Eastern
Washington Friday morning. That track keeps the best chance of
showers over Western WA in the mountains and perhaps a PSCZ but also
suggests a chance for some wrap around rain in the north Cascades at
first. By Saturday morning the low is opening up to more of a trough
and is near the Idaho Panhandle--but some PSCZ precip could still
be going over Western WA. The 12z GFS has a second trough arriving
around daybreak Monday for another round of shower activity.
Camping this holiday weekend may require blue tarps in the mountains
and in the PSCZ, but might not be too bad overall in the lowlands.

&&

.AVIATION...A long wave trough will remain over the West tonight while
an upper level low spins over MT. The air mass over western WA is
stable. The flow aloft is northerly with low level onshore flow at
the surface. Low level stratus clouds cover much of western WA but
ceilings are mainly VFR. The stratus may break up late this
afternoon then reform overnight. MVFR ceilings are possible early
Wednesday morning. 33

KSEA...VFR conditions through this evening. Light N winds
developing 00-03Z then flipping back to S 09-12Z tonight. Ceilings
near 2000 ft early Wednesday morning. 33

&&

.MARINE...Onshore flow will prevail this week with high pressure
over the NE Pacific. Small Craft Advisory winds are likely in the
Central and East Strait of Juan de Fuca during the afternoon and
evening hours each day. 33

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Wednesday for Central U.S.
     Waters Strait Of Juan De Fuca-Coastal Waters From Cape
     Flattery To James Island 10 To 60 Nm-Coastal Waters From
     James Island To Point Grenville 10 To 60 Nm-Coastal Waters
     From Point Grenville To Cape Shoalwater 10 To 60 Nm-East
     Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html





000
FXUS66 KSEW 241747
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
1030 AM PDT TUE MAY 24 2016

.SYNOPSIS...Weak high pressure aloft will be over the area today and
Wednesday. Clouds should break up a bit this afternoon and evening
but then fill back in overnight into Wednesday. An upper low will
bring an increasing chance of showers Thursday through Saturday.

&&

.SHORT TERM...Morning satellite imagery shows the highest peaks and
volcanos sticking up above the clouds in the Cascades. The clouds
over the Olympics are more broken up. There is also an area of lower
marine stratus on the coast. Through tonight there will be low level
onshore flow continuing with weak high pressure aloft. After a
little clearing in the afternoon and evening the clouds will fill
back in overnight. Onshore flow will increase Wednesday in response
to an upper level low beginning to dig south along the British
Columbia coast. The increasing onshore flow will limit the amount of
afternoon sunshine on Wednesday and give slightly cooler max
temperatures versus today. As the upper level low sags south
Thursday and Friday there will be an increasing chance of showers
with stronger onshore flow.

.LONG TERM...The 12z gfs takes the center of the low from the
central B.C. coast on Thursday and drops it SE into Eastern
Washington Friday morning. That track keeps the best chance of
showers over Western WA in the mountains and perhaps a PSCZ but also
suggests a chance for some wrap around rain in the north Cascades at
first. By Saturday morning the low is opening up to more of a trough
and is near the Idaho Panhandle--but some PSCZ precip could still
be going over Western WA.

&&

.AVIATION...A long wave trough remains over the West today while
an upper level low spins over MT. The air mass over western WA is
stable. The flow aloft is northerly with low level onshore flow
at the surface. Low level stratus clouds cover much of western WA
this morning but ceilings are mainly VFR. The stratus should break
up this afternoon for SCT040-060. Patchy low clouds will re-
develop overnight. 33

KSEA...VFR conditions today with SCT040-060 this afternoon. Light
N/NW winds at the surface becoming S this afternoon, then back to
N between 00Z-03Z. 33

&&

.MARINE...Onshore flow will prevail this week with high pressure
over the NE Pacific. Small Craft Advisory winds are likely in the
Central and East Strait of Juan de Fuca during the afternoon and
evening hours each day. 33

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Wednesday for Central U.S.
     Waters Strait Of Juan De Fuca-Coastal Waters From Cape
     Flattery To James Island 10 To 60 Nm-Coastal Waters From
     James Island To Point Grenville 10 To 60 Nm-Coastal Waters
     From Point Grenville To Cape Shoalwater 10 To 60 Nm-East
     Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html





000
FXUS66 KSEW 230336
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
836 PM PDT SUN MAY 22 2016

.SYNOPSIS...An weakening upper trough will result in a mix of
scattered light showers and sunbreaks through Monday. A weak upper
ridge will shift through the area Tuesday and Wednesday. Another
upper trough will move down over the Pacific Northwest for Thursday
through Saturday.

&&

.SHORT TERM...Radar shows showers currently fading with the loss
of daytime heating and becoming more confined to the mountains.
Monday looks similar to today. A weak upper trough over the area
will bring a few showers and some afternoon sunshine. Weak high
pressure aloft should give a mainly dry day Tuesday although
isolated showers will probably bubble up over the Cascades in the
afternoon. Wednesday looks about the same as Tuesday. Temperatures
will be near normal through Wednesday. Schneider

.LONG TERM...Previous discussion...Another upper trough will drop
into the region after the middle of the week--for a return of some
shower activity. The GFS and ECMWF are in pretty good agreement
through Thursday but diverge a great deal over the weekend on how
the upper low evolves and where it drifts.

&&

.AVIATION...The lingering upper level trough will remain the
dominant weather factor over W WA tonight and into Monday as the
associated upper level low slowly treks eastward...currently
centered in southern Alberta crossing into Saskatchewan Monday
morning. As it does so...this should weaken the influence of the
trough.

Cigs generally VFR this evening and breaking up in some
locations...revealing some peaks at the sunset. This will actually
be the case into early tonight...but a weak shortwave disturbance
coupled with a secondary low off the Pacific coast and dipping down
into OR will import another round of moisture...resulting in
increasing clouds overnight and possibly some isolated light showers
or sprinkles. Locations that do see precip may see their cigs drop
into upper-end MVFR...but that condition is not expected to be
widespread. SMR

KSEA...VFR conditions are expected to continue through 06Z with a
predominant SCT-BKN050-070 layer. Surface winds will be SW 5-12 kt.
Kam/SMR

&&

.MARINE...A weak surface trough just W of the WA coast this
evening will drift S over the NW Oregon coastal waters Monday
morning then dissipate. The presence of the surface trough just
offshore will weaken the onshore flow tonight and this should help
to rule out any SCA winds within the CWA. The exception...as
always...may prove to be the strait as obs at Race Rocks are inching
close to SCA criteria...so that may need to be watched...but current
thinking is that winds will still fall short...even if just barely.
While no SCA is planned...would not rule out a short-fused one for
at leas the central strait.

Once the surface trough dissipates Monday afternoon a surface ridge
centered offshore along 140W will become the dominant feature. The
offshore surface ridge will build closer to the WA
coast...increasing the W-SW onshore flow Monday night. This onshore
flow pattern will continue the rest of the week, with SCA W winds
expected to return to the strait during the evenings the rest of
this week. Kam/SMR

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html





000
FXUS66 KSEW 221009
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
309 AM PDT SUN MAY 22 2016

.SYNOPSIS...An upper low over the Pacific Northwest will result in
a mix of mainly light showers and sun breaks the next couple days.
Weak high pressure aloft will bring dry weather in the middle of
next week. Another upper low will move southeast over the area
late in the week for a return to cooler and showery weather.

&&

.SHORT TERM...A large upper trough is still over the region early
this morning, centered near the border of Montana, British
Columbia, and Alberta. Light spotty showers lingered over western
Washington during the night, mainly over the Cascades. Otherwise
weak onshore flow and lots of moisture in the lower 12000 ft of
the atmosphere are keeping skies cloudy. Temperatures at 3 am were
in the upper 40s to mid 50s.

The upper low will move slowly northeast across southern Alberta
today, and a weak upper shortwave extending west from the low will
move south from British Columbia into Washington. The shortwave
combined with low level onshore flow, moisture, and weak
instability will produce some showers again today -- mainly during
the afternoon over the mountains, in the south part of western
Washington, and probably in a weak Puget Sound Convergence zone
over the north sound. There will likely be few if any showers over
much of the greater Seattle metropolitan area, the coast, and the
north interior. It will be only a little warmer today with highs
around 60.

The upper low will move slowly east into southwest Saskatchewan
tonight and Monday, and the upper shortwave will move south of our
forecast area. There will be little change in the weather though,
with mostly cloudy skies and light spotty showers over the
mountains and from around the Seattle area southward. High
temperatures should be a couple degrees higher than today.

The upper trough will weaken Monday night and Tuesday, and drier
light northerly flow aloft will develop over western Washington.
The threat of showers should be limited to the mountains, and any
precipitation should be quite light. The lowlands should have a
bit more sunshine Tuesday with temperatures slightly higher yet.
McDonnal

.LONG TERM...Light northwest flow aloft will continue Wednesday,
ahead of an upper ridge well offshore. However, the leading edge
of another shortwave digging southeast could reach the area late
Wednesday. It should be similar to Tuesday, with partly sunny
skies and a chance of light showers over the mountains. The upper
trough will move southeast across the Pacific Northwest Thursday
and Friday for a better chance of more widespread showers over
western Washington. There is still a chance of showers Saturday,
but we will probably be getting into the somewhat drier northerly
flow on the west side of the upper trough. McDonnal

&&

.AVIATION...An upper level trough will remain over the Pacific
Northwest through the day today and into Monday. The low associated
with this trough is currently centered over western MT. As this low
continues its northeastward path into Alberta...flow aloft will turn
from easterly to become northerly as the morning progresses. The air
mass is expected to remain generally stable and moist...allowing for
MVFR cigs and a chance for showers area-wide today. Cigs may start
lifting during the afternoon somewhat...allowing for locations with
MVFR conditions to possibly creep back into VFR by evening. The very
slow movement of this trough along with a shortwave disturbance
within it will allow for the prospect for showers and low-end
VFR/high-end MVFR cigs to linger into Monday.  SMR

KSEA...VFR cigs over the terminal now will likely lower into MVFR by
sunrise this morning before rebounding to VFR by afternoon. Models
disagree on the prospects of precip today...so have opted to say
there may be showers in the vicinity this afternoon. Surface winds
will remain steadily S to SW. Morning and early afternoon speeds
generally around 10 kts before easing to around 5-8 kts by this
evening. SMR

&&

.MARINE...A weak surface low over Alberta will maintain
weak to moderate W-SW onshore flow through the day today and into
Monday. This flow will help SCA conditions in the Strait to persist
into the morning before starting to taper off. Only ob reading SCA
winds at the time of this writing is Race Rocks...so will leave
Strait in SCA at least through 5 AM PDT.  May need to extend by an
hour or two...but will wait and see.  Cancelled SCA for Puget Sound
and...given how wind speeds are tapering off in the east
Strait...considering dropping it for the N inland waters too. Winds
expected to remain below criteria today and at least into Monday.

Surface low pressure wobbles over portions of southern Canada for
the start of the week...but this will not really impact the onshore
flow pattern very much. Onshore flow should continue through mid
week with varying strength, probably weaker on Monday then stronger
on Tuesday and Wednesday. SCA winds will occur mainly in the
evenings. SMR

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT early this morning for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html





    US Dept of Commerce
    National Oceanic and Atmospheric Administration
    National Weather Service
    1325 East West Highway
    Silver Spring, MD 20910
    Page Author: NWS Internet Services Team
Disclaimer
Information Quality
Credits
Glossary
Privacy Policy
Freedom of Information Act (FOIA)
About Us
Career Opportunities