Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 232135
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
235 PM PDT MON MAY 23 2016

.SYNOPSIS...
A weak upper level ridge will move southeast across the area on
Tuesday through Wednesday. Another upper level trough will move
into the area from the northwest Thursday through Saturday giving
mostly cloudy conditions, a chance of showers, and temperatures a
few degrees below normal. The upper level trough may linger over
the area through the Memorial Day weekend.

&&

.SHORT TERM...
A long wave trough over western North America will linger around
the area for the next several days. The short term portion of the
forecast appears to be pretty much straight forward with an upper
low stalling over the southern Canadian prairies and the low now
off the north central Oregon coast dropping southward. A very weak
upper ridge extending from northern Alberta southwestward to about
50n 140w will slide southeast across our area tonight through
Wednesday.

The passing ridge is quite weak, so expect there to be a small
chance of some convection over the mountains - mainly during the
afternoon and evening hours - Tuesday through Wednesday. At the
surface, high pressure is centered well offshore and will result
in northwesterly flow over the coastal waters. Rather persistent
northwesterly flow with subsidence aloft east of the offshore
ridge is good for the development of stratus offshore and a rather
deep marine layer. This will generally keep high temperatures
across western Washington, despite some sunshine during the
afternoon hours, from warming beyond the 60s. Abundant cloud cover
during the later night and morning hours will hold nighttime
temperatures around the 50 degree mark. Temperatures may be a
couple degrees cooler on Wednesday than on Tuesday as onshore
pressure gradients increase in response to the next upper low over
the Alaskan panhandle that is poised to move southeast into the
area.

Thursday will be cloudier and cooler as onshore flow continues and
the upper low to the northwest moves into the area. Shower chances
will generally increase late in the day Thursday or Thursday
evening as the upper low passes over or by the area. Albrecht

.LONG TERM...
Model consistency and continuity is poor for the upcoming Memorial
Day weekend. Ensembles show quite a bit of spread in 850 mb
temperature and 500 mb height across the region through the period
with some solutions showing the upper low that drops into the
region Thursday night or Friday persisting through the weekend,
and other solutions showing the low moving off to the east with
maybe a ridge over the area by Memorial Day. The deterministic GFS
and ECMWF solutions have both flipped from the cold solution of
last evening to the warmer end of the ensemble envelope, with the
ECMWF flipping less. The deterministic Canadian GEM shows the
first upper low late in the week shifting east and rapidly being
replaced with another rather deep cut off low on Memorial Day.
Given the large ensemble spread and the presence of a long term
trough over the area, a rather persistent mostly cloudy with a
chance of showers forecast is provided with high temperatures near
or a bit below normal. Albrecht

&&

.AVIATION...
A long wave trough remains over the West while an upper
level low spins over MT. The low level air mass is moist with spotty
light showers across western WA this afternoon. Will likely see
patchy MVFR ceilings again overnight through Tuesday morning. The
air mass will remain moist and stable on Tuesday with showers mainly
in the Cascades. 33

KSEA...
VFR conditions through this evening with patchy low clouds
developing overnight. Winds becoming light out of the north by 00Z
then flipping back to S/SW by 12Z tonight. 33

&&

.MARINE...
Onshore flow will increase tonight as a weak surface low
moves inland. High pressure over the NE Pacific will maintain
onshore flow across western WA through the end of the week. Small
Craft Advisory west winds are likely through the Strait of Juan de
Fuca each day, mainly during the late afternoon and evening hours. 33

&&

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

&&

$$

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