549
FXUS66 KSEW 190319
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
819 PM PDT Wed Sep 18 2024

.SYNOPSIS...Weak high pressure holds over the region through Thursday
with morning clouds but afternoon sunshine. Expect a return to a
wetter pattern Friday and again late in the weekend as the next
disturbance crosses the region, though considerable uncertainty
remains in the pattern by early next week.


&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...No major changes have been
made to the forecast this evening. The rest of the previous
discussion can be found below with an update to aviation and
marine components.

Expect a return of low clouds and some patches of fog again
tonight toward daybreak, but another largely dry day is expected
on Thursday with temperatures similar to today, or perhaps a
couple of degrees cooler in a few spots. A passing upper level
disturbance may provide just enough forcing a few light showers in
the mountains late in the day Friday, but these shouldn`t amount
to much and this impulse will largely just provide a reinforcing
push of clouds into the region. A stronger weather system is
likely to approach the region late in the day Saturday. While
it`ll likely remain initially centered to the north, expect rain
chances to return to the far northwestern portions of the area
through the day.


.LONG TERM /MONDAY THROUGH THURSDAY/...Zonal flow remains in
place across the far northeastern Pacific though the weekend,
which will continue to maintain precipitation chances across the
region. Expect the passing trough to bring a more organized shot
of rain (and high mountain snow above 8000 ft or so), and while
QPF amounts trended a little higher (around a tenth to a quarter
inch in the lowlands and a half inch to an inch for the coast and
mountains, highest north), there does remain some uncertainty with
respect to where the moisture plume will end up and if it will
track more into southern B.C. or more squarely across Washington.
As a result, expect to see some fluctuations in the forecast for
the next several cycles and hopefully the ensemble guidance begins
to come into better agreement. Nevertheless, confidence dips even
lower toward the middle of next week with about half of the
guidance favoring a ridge bringing a warm up and some drier
conditions, but still about half of the guidance favoring an
eastern position in the ridge that would leave the region open to
a more active pattern and cooler/wetter conditions. Cullen


&&

.AVIATION...Northwesterly flow aloft as weak upper level ridging
remains offshore. Low stratus with IFR ceilings has begun to
redevelop along the Pacific Coast, with broken low clouds still in
place over the Cascade foothills and valleys. Mostly clear
conditions remain in place across most of the interior of western
Washington. Stratus will continue to redevelop throughout the
overnight period, with ceilings developing at least to IFR levels,
with the potential for some periods of LIFR possible in the early
morning hours just before sunrise. Expecting similar evolution to
this morning where ceilings will slowly rise Thursday morning then
breaking apart 21-23z Thursday afternoon.

KSEA...VFR conditions this evening with a break in the clouds. N/NW
winds around 5 to 8 knots this evening will become light overnight
into Thursday morning. Ceilings will lower once again tonight around
07z-10z to IFR, with at least a 40% chance of LIFR conditions
through 16z.

LH


&&

.MARINE...A surface low will continue to shift southward away from
our area with benign marine conditions over the coastal waters this
afternoon. A weak surface high will expand offshore Thursday into
Friday which will boost northwesterly winds over the outer coastal
waters to small craft advisory levels.

Along with northwesterly winds, combined seas will rise to 7 to 9
feet into Friday, highest in the outer coastal water zones. Seas
will then decrease to 5 to 7 feet into the weekend, as tranquil
conditions return.

Mazurkiewicz


&&

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

$$