Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 201056
Area Forecast Discussion
National Weather Service Seattle WA
356 AM PDT Mon Mar 20 2017
.SYNOPSIS...An upper level ridge will shift east of the area
today with the flow aloft becoming southwesterly. A series of
weather systems embedded in the southwesterly flow will move
through western Washington beginning tomorrow and continuing
through Friday. The best chance for a break in the wet weather
looks to be Thursday. The upper level flow will become westerly
over the weekend with the precipitation type changing to showers.
.SHORT TERM...Hello Spring. Satellite imagery shows high clouds
mainly west and south of the Puget Sound this morning with mostly
clear skies over the remainder of the area. Nothing on the
doppler radars. Temperatures at 3 am/10z were in the 30s and lower
Upper level ridge axis over western Washington early this morning
will shift east later this morning. Flow aloft over the area
becoming southwesterly. This will open the door to a series of
weather systems to move through the area in the next few days. The
first one will move through western Washington on Tuesday with the
rain out ahead of the system as far north as the Southwest
Interior by late this afternoon. Increasing clouds as the day
wears on today with highs in the 50s.
Satellite imagery shows the front is pretty ragged and not well
organized. This trend will continue overnight into Tuesday when
the front will move through the area. At least a chance of rain
for most locations tonight. The exception will be the Northwest
Interior which will stay dry until Tuesday morning. Rain over the
entire area on Tuesday. Plenty of shower activity behind the front
Tuesday afternoon but with lifted indexes positive and little or
zero CAPE will leave thunderstorms out of the forecast. Lows
tonight in the lower to mid 40s. Highs on Tuesday in the upper 40s
to mid 50s.
Another disorganized band of moisture moving up into western
washington late Tuesday night into Wednesday keeping showers in
the forecast. Lows will be mild Tuesday night with lots of cloud
cover, in the 40s. Highs on Wednesday will only be a few degrees
above the lows, in the lower 50s for the most part.
.LONG TERM...Extended models hinting a brief dry period Thursday
with the next system getting pushed to the south by a digging
upper level trough out near 145w. Confidence not real high but
after all of the precipitation in March will try and single out a
dry period on Thursday. System moves into western Washington
Thursday night into Friday for another round of rain. Upper level
trough moving through on Saturday keeping showers in the forecast
with a splitting system approaching on Sunday keeping a chance of
precipitation in the forecast. High temperatures will be a little
below normal through the period, in the upper 40s and lower 50s.
Lows will mostly be in the 40s except for Wednesday night where
lows will be in the 30s to lower 40s. Felton
.AVIATION...An upper ridge over the area will shift inland today
with westerly flow aloft becoming southwest today and southerly
tonight. At the surface, offshore flow will prevail with high
pressure inland and lower pressure offshore. A frontal system will
spread moisture into the area from the south later today and
tonight.. The air mass is stable.
High clouds across the area will lower this afternoon and evening
as a weak frontal system moves into the area from the south. Mid
level clouds will be prevalent tonight.
KSEA...High clouds this morning. Mid clouds will move up from the
south this afternoon and evening. Northerly wind around 10 knots.
.MARINE...Offshore flow will produce small craft advisory easterly
winds at times for the Coastal Waters and western part of the
Strait today. A relatively weak frontal system will move up from
the south tonight. Additional frontal systems - around Tuesday
night and Thursday night - will affect the waters later in the
week for off and on small craft advisory winds for the waters this
.HYDROLOGY...The White river at R Street dropped below flood stage
around midnight and will continue to slowly recede today. No river
flooding is expected in the next 7 days.
The threat of landslides will remain elevated for the next few
days as more rain moves into the area adding to the nearly record
February and March precipitation. Felton
.CLIMATE...For the winter, December 21st through March 19th,
Seattle got 19.87 inches of precipitation. This is 151 percent of
the normal 13.20 inches during this time frame. There was
precipitation on 56 out of the 89 days ( 63 percent ). The 19.87
inches is only the 10th wettest for this time frame at Seattle-
Tacoma airport. Records at the airport started in 1945.
Through March 19th the combined February and March precipitation
for Seattle is 14.23 inches. This is the third wettest February
and March on record including the Federal Building records which
go back to the 1890s. The record is 15.55 inches set in 2014 with
the 2nd wettest 14.85 inches in 1972. There is a chance by the
end of the week Seattle will break this record. Felton
PZ...Small Craft Advisory until 6 PM PDT this evening 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 Point Grenville To Cape Shoalwater 10
To 60 Nm-West Entrance U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory until noon PDT today for Central U.S.
Waters Strait Of Juan De Fuca-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 Out 10 Nm-Puget
Sound and Hood Canal.
You can see an illustrated version of this discussion at