Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 251057
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
357 AM PDT Sat Mar 25 2017

.SYNOPSIS...An upper level trough will move east of the area this
morning. After a brief dry spell tonight another weather system
will bring rain back to western Washington beginning Sunday
morning. Showers behind the front for Monday with another wet
system moving into the area Tuesday and Wednesday. There is a
chance for a dry day late next week.

&&

.SHORT TERM...Satellite imagery shows upper level trough right
along the coast at 3 am/10z with the next system to reach the area
back out near 45n/145w. Doppler radars picking up plenty of
shower activity with the trough with most of the activity west of
the Puget Sound. With mostly cloudy skies over the area
temperatures were in the 40s.

Upper level trough axis moving through western Washington this
morning. Shower activity will decrease significantly behind the
trough. Possible convergence zone development over northern
Snohomish and southern Skagit county later this morning into the
early afternoon hours but with the surface gradients becoming
light convergence zone will dissipate late in the day. Expect a
little bit of sunshine this afternoon but high temperatures will
remain below normal...in the upper 40s to mid 50s.

A brief break in the action tonight with the upper level trough
to the east and the next system still offshore. Rain out ahead of
the front will be near the coast by 12z. Lows will be in the upper
30s to mid 40s.

Next system moving into western Washington on Sunday. Parent low
well north of the area near southern Alaska while the jet stream
is aimed at northern California. The front will get stretched out
a weaken a little as it moves into western Washington late in the
day. This will cut down on the rainfall amounts with less than a
half inch expected in most locations. Highs will the early arrival
of the precipitation will continue to be below normal...near 50.

Trailing upper level trough just along the coast at 12z Monday
keeping showers in the forecast for Sunday night. near the coast
by 12z Monday. Upper level trough axis moving through western
Washington Monday morning with the shower activity becoming
confined to the coast and mountains in the afternoon. Another
convergence zone near the Snohomish/Skagit county line possible
Monday afternoon. Highs will continue to be cool...in the upper
40s to mid 50s. Lows on Sunday night will be in the upper 30s to
mid 40s.

.LONG TERM...Extended models in good agreement with yet another
front approaching western Washington on Tuesday. The front stalls
over the area Tuesday night into Wednesday. Strong southwesterly
flow aloft with enhanced precipitation along the south slopes of
the Olympics. Upper level trough moving through Thursday morning
with drying northwesterly flow aloft behind the trough later in
the day on Thursday. Race Thursday night into Friday between an
approaching warm front and a building upper level ridge over
western Washington. 00z run gives the ridge the upper hand and
pushes the warm front north of the area. Will stay with a dry
forecast for day 7. Felton

&&

.AVIATION...An upper level trof of low pres over the region early
this morning will cont moving east and will be over ID this
afternoon. Contd wly flow aloft. Low level sly or onshore flow will
cont diminishing. Expect areas of MVFR CIGs, with areas of MVFR
VSBYs with heavier showers. The mtns will be partially obscd.

KSEA...Expect ocnl MVFR CIGs, mainly this morning. Heavier showers
will also lower the visibility in the MVFR category range this
morning. VFR conditions are anticipated this afternoon thru tonight.
Sly winds will slowly diminish during the day today, becoming light
and variable tonight.

&&

.MARINE...
A 1020 mb high will develop over the far southwest WA coast this
afternoon, and this will cause the onshore flow to weaken. The flow
will become easterly or offshore tonight in response to falling
pressure over the offshore waters. An occluded front is expected to
move across the area Sunday night. Gale force southeasterlies are
possible over the coastal waters, beyond 10 NM, on Sunday ahead of
the front. Expect another frontal system to impact the area on
Tuesday.

&&

.HYDROLOGY...No river flooding is expected for the next 7 days
with the exception of the flood prone Skokomish river where
enhanced rainfall amounts along the south slopes of the Olympics
Tuesday night int Wednesday could be enough to get the river to
flood stage. Felton

&&

.CLIMATE...With 0.24 inches yesterday the monthly precipitation
total for Seattle is now 6.11 inches. Combined with the 8.85
inches in February this is only the 3rd time since weather records
started in Seattle in the 1890`s that both February and March have
gotten 6 inches plus of precipitation. The other two occurrences
2014 and 1972. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Watch from Sunday morning through Sunday afternoon 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 for hazardous seas until 3 PM PDT this
     afternoon 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 until 9 AM PDT this morning for West
     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



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