Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 241453
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
753 AM PDT Wed May 24 2017

.SYNOPSIS...Following last evening`s strong cold front, a much
cooler air mass will reside over Western Washington today, with
onshore flow aiding the development of a few showers, mainly over
the mountains. Temperatures will slowly rebound on Thursday, with
enough moisture and instability for a few afternoon showers and
thunderstorms over the Cascades. A warm and dry upper ridge axis off
the coast on Friday will pass directly over Western Washington on
Saturday. Its warm and dry influence will continue on Sunday and
Memorial Day.

&&

.SHORT TERM...Last night`s upper trough axis will continue to exit
off to the east today. A much cooler low-level air mass is in
place today, and onshore flow will continue to lead to clouds and
a few light showers over the mountains.

A disturbance will dive down into Central Washington on Thursday
in northerly flow aloft. The main meteorological impact will be
to steepen low-mid level lapse rates and give rise to convective
instability over the mountains, more notably the Cascades. CAPE
values will peak around 400-600 J/kg over the Cascades, and
northerly mid-level speed shear will enhance lift as well. So
looking for a few late afternoon and early evening showers and
thunderstorms over the Cascades on Thursday PM.

A well-amplified upper ridge axis will pass east across 130W on
Friday. Upper heights will rise quickly over the Pac NW, and the
cooling low-level onshore flow component will weaken further.
These will all support a hearty day-over-day rise in afternoon
temperatures and a dry forecast on Friday.  Haner

.LONG TERM...From Previous Discussion: The Memorial Day weekend
looks to be generally rain- free as upper level ridging makes its
way eastward over the area. Afternoon high temperatures will
hover right around 80 degrees for most of the interior lowlands
during this time frame while temperatures along the coast will
prove more mild in the mid to upper 60s. A shortwave disturbance
embedded within the passing ridge may give rise to some convective
showers Sunday afternoon and evening...but this appears to be
confined to the Cascades at this time. In fact...this
afternoon/evening pattern under a fairly stationary ridge looks to
persist into the first part of next week. While certainly would
not rule out a rumble of thunder with these showers...this is far
out enough in the extended where not much in the way of confidence
in inserting that feature into the forecast at this time. As
mentioned before...this activity looks to be confined to the
mountains with continued dry conditions expected for the lower
elevations.

As the ridge remains fairly stationary...so too will area
temperatures...which means afternoon highs right around 80 will
linger over the interior lowlands at least into the first part of
next week.  SMR

&&

.AVIATION...Northerly flow aloft will prevail today and tonight
with an upper ridge offshore and an upper trough inland. At the
surface, onshore flow will gradually ease with high pressure
offshore and lower pressure inland. The air mass is slightly
unstable with areas of low level moisture.

KSEA...Some VFR low clouds at times this morning with clouds
becoming generally more scattered in the afternoon. Southerly wind 5-
10 knots will become northwest this afternoon. Schneider

&&

.MARINE...High pressure will be offshore with lower pressure
inland today and tonight with small craft advisory winds over
most of the waters gradually coming down as onshore flow eases.
Relatively short period 10 foot swell over the Coastal Waters will
also gradually subside today and tonight.

Onshore flow will continue for the next several days but gradually
weaken and turn a bit more northerly as a weak thermal trough
develops to the south late in the week. Schneider

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 11 AM PDT Thursday 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 8 PM PDT this evening for Coastal
     Waters From Cape Flattery To James Island Out 10 Nm-Coastal
     Waters From James Island To Point Grenville Out 10 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater Out
     10 Nm.

     Small Craft Advisory until midnight PDT tonight for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 3 PM PDT this afternoon for Northern
     Inland Waters Including The San Juan Islands.

     Small Craft Advisory until 5 PM PDT this afternoon for West
     Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$

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