Scientific Forecaster Discussion
fxus66 ksew 241023
Area forecast discussion
National Weather Service Seattle Washington
320 am PDT Wed may 24 2017
Synopsis...a much cooler air mass over western Washington today
will result in cooler conditions and a slight chance of showers
today. Temperatures slowly rebound Thursday with a slight chance for
showers and thunderstorms over the Cascades. An upper ridge will
bring warmer and drier weather over the weekend.
Short term...winds continue to gradually ease this early morning
thus allowing for inherited headlines to expire. Temperatures
continue to fall with many locations reporting temperatures ranging
from the mid 40s to lower 50s. This Marks a significant departure
from 24 hours ago where...using sea-tac as an example...current obs
are 10 degrees cooler. Not surprisingly...with a cooler air mass in
place on the back side of an upper level trough...temperatures today
will actually end up falling pretty close to normal or just a little
shy of normal even though temps this afternoon will be 10 to 15
degrees cooler than observed highs for yesterday.
This flirtation with normalcy will not last long. As the upper level
trough pulls away and upper level ridging starts to build over the
Pacific...so too will temperatures rise once more...gradually at
first...as temperatures on Thursday will range from the mid 60s to
right around 70 but as the upper level ridge starts to enter the
area Friday temperatures will once again start to inch up to the 80
While the near term looks generally dry...some
disturbances/instability in the wake of the trough axis will bring
slight chance pops to The Lowlands today and chance pops to the
Cascades and Olympics today and again tomorrow. Conditions look
unstable enough over the southern half of our Cascades to allow for
the chance of thunderstorms Thursday afternoon. This is a bit of
fine tuning from previous forecast. The mountains appear to be the
limit of any precip though as lowlands are expected to resume a dry
Long term...the Memorial Day weekend looks to be generally rain-
free as upper level ridging makes its way eastward over the area.
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...an upper level low over SW British Columbia will
continue moving east. An upper level ridge centered well offshore will
build over the region in its wake. Strong westerly flow aloft will weaken
and become northerly during the day today. Moderately strong low level
onshore flow will grdlly weaken. Expect areas of MVFR cigs this
Ksea...expecting VFR conditions thru tonight. There is a possibility
of brief MVFR cigs this morning. Winds will be problematic this
morning. Overall, anticipating winds to veer to southerly by
midmorning before becoming northwest this afternoon.
a 1039 mb high over the northeast Pacific will gradually weaken
through Friday. The combination of higher pressure offshore with
lower pressure east of the Cascades will result in continued
onshore or westerly flow; although, the flow will weaken with time.
Pz...Gale Warning until 6 am PDT early this morning for central U.S.
Waters Strait of Juan de Fuca-East Entrance U.S. Waters
Strait of Juan de Fuca.
Small craft advisories are in effect for the remaining waters.
Small Craft Advisory for rough bar until 6 am PDT early this
morning for Grays Harbor bar.