Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 221034
Area Forecast Discussion
National Weather Service Seattle WA
330 AM PDT FRI JUL 22 2016
.SYNOPSIS...An upper level trough passing over Western Washington
this morning will allow for the possibility for showers and
thunderstorms to continue into the early afternoon before activity
is expected to taper off. A weak upper ridge should bring sunny
weather Saturday through Thursday with warming temperatures.
.SHORT TERM...Certainly more activity this early morning than what
was expected...as...like an overactive child that does not want to
go to bed...radar has been active much of the late night/early
morning. West side of the Olympic peninsula has seen the most action
during the overnight hours and still seems to be a hot bed of
activity...now starting to see far southern portions of the CWA get
into it too. This actually really gells well with the latest HRRR
runs showing a couple of vorticity maxima that look to shoulder the
blame for this. Furthering this belief is looking at the surface LI
values...which are rather anemic. If the HRRR continues to hold
true...could see additional thunderstorms later on in the morning
make their way over the San Juans and Western Whatcom county. All
that being said...have updated inherited forecast to allow for a
larger area of slight chance of thunderstorms to persist into the
late morning hours. Should start to see this stuff mosey on
elsewhere for the afternoon and evening.
Thankfully the immediate near term has been busy...otherwise this
would be a short discussion. Ridging starts to build in over the
area this evening drying things out and warming temperatures over
the weekend. Today looks to be the coolest day in the forecast with
inland temps generally in the low 70s. After this...it is off to the
races as temps increase to the mid 70s tomorrow and mid to upper 70s
Sunday. While there might be some lingering clouds into Saturday
afternoon...after that...nothing but mostly clear skies. SMR
.LONG TERM...As the new week approaches...the ridge flattens out to
a more zonal flow. Models continue to show a shortwave that looks to
move through on Monday...but really makes no impact on the area. The
aforementioned zonal flow resumes through mid week before a stronger
ridge looks to lock into place over the Pacific Northwest.
Temperatures will continue to climb with the potential for inland
locations to see close to 90 degrees by the second half of next
week. So...for those who wondered where summer was...there is that
old phrase about being careful of what one wishes for. SMR
.AVIATION...An upper level low center will steadily move ne across
wrn WA this morning, eventually reaching NE WA this afternoon.
While the upper low remains overhead, the mid-level air mass will
remain moist and unstable. This has led to quite a few
thunderstorms overnight. Thunderstorms will start to diminish
after 15z, when the upper low starts to exit. The mid-level air
mass will become drier this afternoon, but a deep marine layer
will keep the low-levels moist and stable. Speaking of the marine
layer, IFR cigs in marine stratus will be widespread this morning.
Some lifting expected this afternoon, but scattering will be
difficult. Flow aloft becoming light to moderate northwest this
KSEA...Center of the upper low will pass directly across the
terminal through 14z, supporting thunder at the terminal until
then. Based on radar trends, may be hard to miss on thunder early
this morning. Otherwise, IFR cigs of 010-018 in the marine layer
will prevail this morning. Cigs lifting to 030-040 this afternoon
but having a tough time actually scattering. Yet another round of
IFR cigs in the marine layer on Saturday morning.Haner
.MARINE...UIL-BLI gradient now weakening, and Race Rocks just fell
below gale force. Gale Warning will downgrade to Small Craft
Advisory after sunrise. Will still maintain Small Craft westerlies
through the central and eastern Strait for the next 24 hours, and
over the Northern Inland Waters too for much of the day.
Otherwise, moderate onshore flow will prevail for the next week
with the typical summertime diurnal peaks and dips in the speed.
PZ...Small Craft Advisory from 7 AM this morning to 5 AM PDT Saturday
for Central U.S. Waters Strait Of Juan De Fuca-East
Entrance U.S. Waters Strait Of Juan De Fuca.
Gale Warning until 7 AM PDT this morning for Central U.S. Waters
Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
Juan De Fuca.
Small Craft Advisory until 9 AM PDT this morning for Northern
Inland Waters Including The San Juan Islands.
You can see an illustrated version of this discussion at