Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 191057
Area Forecast Discussion
National Weather Service Seattle WA
357 AM PDT Sun Mar 19 2017
.SYNOPSIS...Isolated showers over the northern portion of the
area will come to an end this morning as high pressure builds over
western Washington. The high will shift east of the area on
Monday allowing a weather system to reach the area from the
southwest late in the day. Rain out ahead of the system will
arrive late Monday afternoon into Monday evening. The system will
move through western Washington on Tuesday. Unsettled weather
will continue Tuesday night into the weekend.
.SHORT TERM...Satellite imagery shows some pesky showers hanging
on north of a line from about Hoquiam to Mount Baker. Just some
high clouds over the remainder of the area. Temperatures at 3
am/10z are mostly in the 30s with many locations below freezing
along the Hood Canal and from Tacoma southward.
Showers over the north will come to an end this morning as an
upper level ridge begins to build offshore and the low level flow
turns offshore. Cloud cover will also thin out over the northern
portion of the area leaving mostly sunny skies across western
Washington this afternoon. Temperatures aloft are not very warm,
850 mb temperatures in the -1 to -5c range this afternoon, so even
with the sunshine and increasing offshore flow expect highs to
only be at or just a little below normal today, in the upper 40s
to mid 50s.
Upper level ridge axis moving over western Washington tonight. In
the lower levels offshore flow will continue into Monday morning.
It will be another cool night with locations from about Tacoma
southward once again near or a couple of degrees below freezing.
For the remainder of the area lows will be in the 30s.
Upper level ridge axis moving east of the area on Monday. Flow
aloft becoming south southwesterly. This will open up the door for
the next system to reach the area. Model trends have been speeding
up the timing of the arrival of this system with the latest runs
spreading rain as far north as Forks along the coast and to
Seattle over the interior by 00z Tuesday. Have increased the pops
along the coast and over the southwest Interior in the afternoon
on Monday. Highs will be in the upper 40s to mid 50s.
Flow aloft remaining south southwesterly Monday night into Tuesday
with the front not moving through western Washington until Tuesday
morning. Plenty of showers behind the front Tuesday afternoon. Highs
will continue to be in the upper 40s to mid 50s. Lows Monday
night will be much warmer with the cloud cover, in the lower to
.LONG TERM...The unseasonably wet weather will continue through
the extended period. The models are in good agreement with an
upper level trough offshore Wednesday moving through the area on
early Thursday keeping pops in the likely or higher category.
Another front arriving on Thursday night into Friday but the jet
stream is aimed at northern California and the front is splitting
as it makes its way into Western Washington. Will only go with
chance pops for now with the system. Another upper level trough
moving through western Washington on Saturday keeping showers in
the forecast. Felton
.AVIATION...A weak upper ridge will build over the area today and
tonight with westerly flow aloft. At the surface, northerly
offshore flow will develop today as high pressure builds into
southern British Columbia. Offshore flow will increase and turn a
bit more easterly tonight. The air mass is generally dry and
Clouds will be generally scattered today but there will be some
mid level clouds at times, especially over the mountains and the
north part this morning. Patchy fog is also possible in the south
interior this morning.
KSEA...Scattered mid clouds at times today. South wind 3-6 knots
this morning will become north 5-10 knots this afternoon. Schneider
.MARINE...Northerly offshore flow will develop today as high
pressure builds into southern British Columbia. Offshore flow
will increase and become a bit more easterly tonight and Monday.
Small craft advisory easterly winds are expected at times for the
western two thirds of the Strait of Juan De Fuca and the Coastal
Waters tonight and Monday.
A series of troughs will move through the waters, roughly one
every 24 hours, Monday night and through Thursday. Schneider
.HYDROLOGY...The flood warning for the Skokomish ended Saturday
evening. The White river at R street is just above flood stage
early this morning but has been receding overnight. The White
will drop below flood stage this morning.
Additional river flooding is not expected in the next 7 days but
the Skokomish will be running high at times with additional
rainfall over the south slopes of the Olympics.
The landslide threat will remain elevated for the early part of
the week with soils saturated from the well above normal March
.CLIMATE...With the 0.34 inches on Saturday, the February and
March precipitation total for Seattle is now 14.23 inches, the 3rd
highest total in over 120 years of records. The only two years
that are higher 15.55 inches in 2014 and 14.85 inches in 1972.
There have been 5 days in March with at least a half inch of rain
in Seattle. There are only two years with more days with 0.50
inches or more in March on record, 2014 with 8 days and 1916 with
6 days. Felton
PZ...Small Craft Advisory from 6 PM this evening to noon PDT Monday
for Central U.S. Waters Strait Of Juan De Fuca-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-West Entrance U.S. Waters
Strait Of Juan De Fuca.
You can see an illustrated version of this discussion at