Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 191643
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
943 AM PDT Sun Mar 19 2017

.SYNOPSIS...High pressure will build over Western Washington
today. The high will shift east of the area on Monday, opening the
door to a weather system which will spread rain up from our south
late Monday afternoon and Monday night. An approaching cold front
will again enhance precipitation on Tuesday night. Unsettled
weather will continue Wednesday into the weekend.


&&

.SHORT TERM...A drying trend will continue across Western
Washington through tonight. A surface high pressure center over
northern Vancouver Island right now will shift eastward across the
interior of B.C. tonight. This will cause drying low-level
northerly and then easterly flow to strengthen and peak on Monday
morning. The few remaining showers near the Coast and over the
North Cascades will shrivel up and die off over the course of
today. So a much-needed dry break is essentially underway and will
continue until Monday PM.

Flow aloft will back from westerly to southwesterly on Monday,
then become southerly on Monday night, then strengthen on Tuesday.
On Monday PM, this will bring up plenty of mid-high level
moisture. Falling upper heights and shortwave energy coming up
from the south will eventually help precip spread up from the
south. Updated the forecast earlier this morning to slightly slow
down the onset of precip on Monday PM. Appears that dry low-level
offshore flow will continue into Tue AM and retard the speed with
which the air mass can moisten sufficiently for precip. On Monday
night, looks like a more organized front will spread up from the
south and finally cause rain to overspread most or all of Western
Washington.

Following Monday night`s round of rain, may be some dry breaks on
Tuesday, but some disorganized dribs and drabs of rain will
continue in the moist southerly flow aloft. Precip will blossom
again on Tue night and Wed morning with the approach of a cold
front from the Pacific, peaking on Tue night. Haner

.LONG TERM...From Previous Discussion: 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, high pressure
over Western Washington this morning will shift into eastern
portions of Washington and southern portions of British Columbia
tonight and Monday. The air mass will be stable and dry.

Patchy shallow fog early this morning will burn off by 18Z. The
remnants of an old convergence zone from northeast of Whidbey
Island to east of Bellingham will dissipate. As weak ridging aloft
develops over the area today, expect the isolated showers seen
offshore to dissipate as well. By this afternoon through tonight,
expect good VFR conditions with only a scattered to broken cirrus
layer.  Albrecht

KSEA...Scattered to broken thin cirrus through Monday morning.
Light southeasterly wind this morning will become northerly by 22Z
and will increase to 10-15 knots tonight and early Monday.
Albrecht

&&

.MARINE...High pressure over the waters early this morning will
shift north and east into southern British Columbia and eastern
Washington tonight and Monday. Expect increasing offshore pressure
gradients as the high shifts northeastward. Small craft advisories
are in effect for tonight into Monday for the increasing
northeasterly and easterly winds over the coastal waters and
through the western two thirds of the Strait of Juan de Fuca.

A series of difficult to time troughs will move northeastward
across the waters, roughly one every 24 hours, Monday night
through Thursday. Each of these may bring small craft advisory
conditions at times to the coastal waters and portions of the
Strait of Juan de Fuca. Albrecht

&&

.HYDROLOGY...All area rivers are falling right now, except for the
lower reach of the Chehalis (which is below flood stage), owing to
mostly dry weather right now. The only river remaining above flood
stage as of 9 AM is the White river at R street. It, too, is
receding and should drop below flood stage within the next few
hours.

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
rainfall. Haner

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
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.

&&

$$

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