Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 232240
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
340 PM PDT Tue Apr 23 2019

.SYNOPSIS...Onshore flow and a Convergence Zone will give a
chance of showers to the Cascades and central Puget Sound area
this evening. A weak ridge of high pressure will give partly
sunny and dry conditions on Wednesday. Clouds will increase on
Thursday as onshore flow develops, but conditions will remain dry.
A weak trough and low level onshore flow will give a chance of
showers, mainly to the mountains and northern portions of the
interior Friday into early next week.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...Radar and satellite imagery
show onshore flow producing a convergence zone from the Cascades
of Snohomish and Skagit counties westward across Everett, the
northern Kitsap Peninsula and the Port Townsend area. This area of
convergence will likely stay about where it is this evening then
slowly dissipate overnight. A chance of showers continues for
these areas through the evening hours.

A broad and progressive upper ridge will give low level northerly
flow to the area as well as drying on Wednesday. Highs will be
mainly in the upper 50s to mid 60s.

A broad and weak upper trough will approach the area from the west
on Thursday. A rather thick layer of moisture in the mid and upper
levels will bring increasing clouds to the area through the day,
then some lower clouds will spread inland during the evening hours
as low level flow becomes onshore ahead of the incoming trough.
Despite the cloud cover, expect highs to be in the 60s. Despite
the increase in moisture aloft, expect it to remain dry.

The broad trough with increasing flow aloft will give partly to
mostly cloudy skies to the region on Friday along with an
increase in onshore flow and a chance to slight chance of showers
(mainly to the Cascades and northern portions of the area).
Onshore flow will result in daytime temperatures falling a few
degrees, back to around the 60 degree mark. Albrecht

.LONG TERM /SATURDAY THROUGH TUESDAY/...Troughing will dominate
conditions over the weekend. Models continue to show mainly only
chance pops with partly to mostly cloudy conditions across the
region. Snow levels will be low, as low as 3000 ft or so at times,
so some snow showers may be seen in even the lower passes.
Precipitation amounts appear that they will be rather light, so
no significant impacts are expected at this time.

Models generally agree that the early week period will be
dominated by a weak trough that will provide partly to mostly
cloudy conditions with a chance of showers and temperatures near
normal for late April. While models do show a good deal of
consistency today, their continuity with previous solutions is
not good. Forecasts represent a blend of the ECMWF with the
National Blend of Models. Albrecht

&&

.AVIATION...A weak ridge will build over western Washington on
Wednesday. Satellite imagery has indicated clouds breaking up over
portions of the region this afternoon, with current conditions
ranging from VFR to MVFR across the board. Guidance suggests that
ceilings could become MVFR tonight, but it does seem likely there
will be more clearing on Wednesday. Westerly winds aloft will
become northwesterly during the overnight hours. Surface winds
for terminals along sound are southerly in the 10-15kt range with
a few gusts near 20kts. Winds then turn to the E/NE for terminals
near the south sound tonight.

KSEA...VFR cigs this afternoon. Cigs could drop back down to MVFR
during the overnight hours, however are expected to lift back to
VFR early Wednesday. Southwesterly winds 10-15 knots, becoming
more east- northeasterly tonight.

Borth

&&

.MARINE...Onshore flow will persist across the coastal waters
tonight and will continue to bring a strong push of westerly flow
down the Strait of Juan de Fuca. Recent observations have already
indicated gale strength westerlies in the central Strait this
afternoon, while winds have recently started to pick up in the
eastern Strait. SCA strength winds will likely bleed in to nearby
Admiralty Inlet and Northern Inland Waters. Have also issued a SCA
for Puget Sound this afternoon, as observations have indicated
gusty southwesterlies in the southern portion of the Sound. Northwesterly
SCA strength winds will remain possible for waters in the northern
Sound. Winds will die down in the Strait early on Wednesday, however
northerly SCA strength winds will continue into the morning hours for
the coastal waters.

Borth

&&

.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will be updated as needed until
then.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 8 PM this evening to 8 AM PDT
     Wednesday for 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.

     Small Craft Advisory from 8 PM this evening to 5 AM PDT
     Wednesday for Coastal Waters From Cape Flattery To James
     Island Out 10 Nm-Coastal Waters From James Island To Point
     Grenville Out 10 Nm-Coastal Waters From Point Grenville To
     Cape Shoalwater Out 10 Nm.

     Gale Warning until 3 AM PDT Wednesday for Central U.S. Waters
     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory until 3 AM PDT Wednesday for Northern
     Inland Waters Including The San Juan Islands.

     Small Craft Advisory until 5 AM PDT Wednesday for Admiralty
     Inlet.

     Small Craft Advisory from 8 PM this evening to 2 AM PDT
     Wednesday for Puget Sound and Hood Canal.

&&

$$

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