Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 090427
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
827 PM PST Mon Mar 8 2021

.SYNOPSIS...Upper level low off the coast will move slowly south
tonight and Tuesday moving into Northern California Wednesday.
Weak systems spinning out of the low moving through Western
Washington tonight and again Tuesday. Weak upper level trough
dropping down from the north Wednesday. Upper level ridge over the
area Thursday and Friday with a frontal system moving into the
area over the weekend.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...There`s a compact mesolow
spinning north over the Coastal Waters tonight, with showers
clipping the area. The larger/broader main area of low pressure
remains over the offshore waters and will continue to sag south.
Temperatures overnight will be a few degrees warmer with lows
mostly in the mid to upper 30s. 33

Previous discussion...Low continues to drop south southeast
Tuesday night with the low weakening and moving inland over
Northern California Wednesday. Low far enough south Tuesday night
to keep the weak systems spinning out of the low south of the
area. Weak upper level trough moving down out of the north
Wednesday for another chance of showers Wednesday afternoon
especially for the eastern half of the area. Lows in the lower to
mid 30s Tuesday night with highs Wednesday similar to Tuesday.

Drying north northeasterly flow aloft developing Wednesday night
as an upper level ridge noses into British Columbia. With the
clearing skies many places Thursday morning will be at of below
freezing.

Upper level ridge moving south with the ridge axis right over
Western Washington Thursday afternoon. Thursday looks to be the
day with the most sunshine in the short term after areas of
morning fog and low clouds dissipate. Highs in the upper 40s to
mid 50s.

.LONG TERM /FRIDAY THROUGH MONDAY/...Flat upper level ridge over
the area Friday for another dry day. Deterministic models pretty
emphatic about a wet system moving into Western Washington over
the weekend. The ensemble members are less enthusiastic about the
front. Model blend only gives chance pops at this point. Will stay
with that for now. Ensembles are trending toward higher pops so
if anything look for the pops to increase for the weekend in
future forecast packages. Drying northerly flow aloft developing
later Monday behind the front but lingering trough will keep a
slight chance of showers in the forecast. Highs in the 50s Friday
and Saturday cooling to the mid 40s to lower 50s Sunday and
Monday. Felton

&&

.AVIATION...An upper low and an associated surface low well
offshore will slowly shift south tonight and Tuesday. A weak
upper level disturbance in the flow aloft will move through the
area tonight. This low is bringing in some rain shower to the
Western Washington area. Most of these showers are fairly light,
with the exception being near the coastal sites such as KHQM. But
overall these showers will remain fairly scattered as this mesolow
tracks northward. Another low will move into the area from the
south on Tuesday. Which will brining in another round of scattered
showers.

KSEA...Mid level clouds tonight and Tuesday with a few spots of
rain. Scattered showers will remain in the area during the
overnight, and if one to pass over the airport ceilings will
likely lower during its passing. Winds are expected to be
relatively light and from the east to southeast.

Schneider/Butwin

&&

.MARINE...A compact mesolow may bring gales to the Coastal Waters
tonight. A larger/broader low well offshore will shift south
tonight and Tuesday. This low will bring small craft advisory
strength east to southeast winds at times to the Coastal Waters,
Strait of Juan de Fuca, and Northern Inland Waters through
Tuesday. West swell 10-12 feet over the Coastal Waters and West
Entrance Strait of Juan de Fuca will subside below 10 feet tonight
and Tuesday.

Weak high pressure will be over the area Wednesday through
Friday. A front will reach the area on Saturday. 33/Schneider

&&

.HYDROLOGY...River flooding is not expected through the next
seven days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 4 AM to 4 PM PST Tuesday for Coastal
     Waters From Cape Flattery To James Island 10 To 60 Nm-
     Coastal Waters From Cape Flattery To James Island Out 10 Nm-
     Coastal Waters From James Island To Point Grenville 10 To
     60 Nm-Coastal Waters From James Island To Point Grenville
     Out 10 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville
     To Cape Shoalwater Out 10 Nm.

     Gale Warning until 4 AM PST Tuesday for Coastal Waters From Cape
     Flattery To James Island 10 To 60 Nm-Coastal Waters From
     Cape Flattery To James Island Out 10 Nm-Coastal Waters From
     James Island To Point Grenville 10 To 60 Nm-Coastal Waters
     From James Island To Point Grenville Out 10 Nm-Coastal
     Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater Out
     10 Nm.

     Small Craft Advisory until 4 AM PST Tuesday for Grays Harbor Bar.

     Small Craft Advisory until 4 PM PST Tuesday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca-Northern Inland Waters Including The
     San Juan Islands.

&&

$$

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