Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 302145
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
245 PM PDT MON MAY 30 2016

.SYNOPSIS...
Upper level ridging will move slowly east across western
Washington tonight and Tuesday bringing mainly clear skies and a
short warming trend. A marine push will begin Tuesday night and
strengthen on Wednesday as a weak weather system moves across the
area. The system will bring increasing clouds Wednesday and a
chance of showers Wednesday through Thursday night. A stronger
upper level ridge will build into the area next weekend giving
sunny skies and much above normal temperatures.

&&

.SHORT TERM...
A ridge of high pressure aloft sits along 128N while a 1027 mb
high sits off the northern tip of Vancouver Island. The high off
Vancouver island will bridge eastward across British Columbia
tonight into Tuesday giving low level north to northeast flow for
good warming. The offshore flow will remain strongest to the south
of the area on Tuesday, so thermal troughing expanding northward
across western Oregon will stay to the south of the forecast area
on Tuesday then move off to the east of the cascades Tuesday night
and Wednesday as a short wave trough and associated weak frontal
system moves into the offshore waters and induces a marine push.
The high temperature from about Seattle southward will be 80 or
above on Tuesday with areas to the north and along the coast
holding in the 70s.

It appears that Wednesday will be mainly cloudy, cooler, and will
feature onshore flow all day. The offshore front will brush the
northern portion of the Olympic peninsula Wednesday and Wednesday
night, so a chance of showers will be included in the forecast
there. A second short wave trough and frontal system will move
into the area later Wednesday night and Thursday. The Canadian GEM
and ECMWF are wetter with this second front than the GFS. At this
time a model consensus was used to initialize the forecast for
the period through Thursday night. Thursday will likely see
temperatures in the 60s to lower 70s. Albrecht

.LONG TERM...
An active weather pattern over the east central Pacific with a
storm track outside of 130-140W will promote ridging over the
western United States. Global models and their ensemble members
all agree that a hot and strong ridge over the Desert SW on
Thursday will build into the area from the southeast over the
weekend, with its amplitude and subsidence aided by an upper level
low near San Francisco on Sunday that will tend to move northward
with time. 500 mb heights on Saturday rise to around 588 dam while
850 mb temperatures rise to 18-20C. With the ridge building in
from the southeast, thermal troughing will tend to develop east of
the Cascades leaving high heights and warm air aloft to combine
with light onshore flow at low levels. This will promote highs in
the mid to possibly upper 80s in the interior of western
Washington with dewpoint temperatures in the mid and upper 50s.
Low temperatures over the weekend will have a hard time dropping
much below 60. With the trend in the long term model solutions,
high and low temperatures were increased Friday through Sunday.

The ridge moves off to the east a bit later Sunday through early
next week while the upper low to our south opens up and lifts
northward through our area. This will promote an increase to low
level onshore flow for a cooling push and a chance of showers or
thunderstorms -mainly over the Cascades. Albrecht

&&

.AVIATION...
An upper level ridge offshore will shift over
Washington tonight and Tuesday. Northwesterly flow aloft becoming
westerly on Tuesday. The air mass is stable and dry.

Mostly clear skies through Tuesday with a few high clouds passing
through.

KSEA...Clear skies with northerly wind 5-9 kt becoming northeasterly
after 05z. Felton

&&

.MARINE...
Thermally induced low pressure will expand northward
along the coast tonight. This will maintain northerly flow
over the waters.

The low will shift inland Tuesday morning with increasing onshore
flow Tuesday afternoon. Winds will reach small craft advisory
criteria in the central and east portions of the Strait of Juan de
Fuca Tuesday night.

Low level onshore flow will continue on Wednesday with another round
of small craft advisory westerlies Wednesday afternoon into
Wednesday night for the central and eastern Strait. There is a
chance the onshore flow will be strong enough for gale force winds
Wednesday evening.

Surface high pressure will remain over the waters Thursday and
Friday with light surface gradients. Felton

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...None.
&&

$$

www.weather.gov/seattle

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