Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 231604
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
904 AM PDT Wed Oct 23 2019

.UPDATE...A Dense Fog Advisory has been issued for the SW interior
and areas near the souther portion of Puget Sound, as observations
in this vicinity have indicated visibility reductions of 1/4 mile
or less during the morning commute. The advisory does include the
I-5 corridor from Olympia to Tacoma and also Olympia to Chehalis.
Use caution if traveling this morning and give yourself some extra
time.

In addition to the fog, one river remains above flood stage-the
Snoqualmie River near Carnation. The river is expected to fall
below flood stage later today.

Remainder of the forecast is on track this morning with no changes
planned. Fog should gradually dissipate with daytime heating this
morning. Mostly sunny skies should be the rule for today, with
just some passing high clouds.

Kovacik

&&

.PREV DISCUSSION... /issued 242 AM PDT Wed Oct 23 2019/

.SYNOPSIS...High pressure aloft will bring dry weather to the
region through Thursday. A fast moving system will bring some rain
to the area on Friday. Cool, dry northerly flow will then develop
over the weekend and into early next week for a return of dry
weather along with seasonable days and chilly nights.

&&

.SHORT TERM /TODAY THROUGH FRIDAY/...Upper level ridging is
building into the region today for a much-needed break in the
weather. Areas of low level moisture persist and, with light
surface gradients, will lead to areas of stratus and patchy fog
this morning. Low level northerly flow is expected to increase
toward afternoon and this along with the strengthening upper ridge
should help clear most places out. With some sunshine, high
temperatures will be near or a little above average.

Heights continue to rise tonight and Thursday as the ridge axis
shifts eastward. Much like this morning, there should be areas of
stratus and patchy fog across the area in the morning. The ridge
loses some amplitude and will likely become a little dirty at our
latitude. There will be a little more in the way of high level
clouds filtering in the area, but not enough to preclude a partly
to mostly sunny forecast. The flow aloft buckles on Friday
allowing a fast moving system to clip the region. Best chances of
rainfall with this system will be from about Snohomish County
northward Friday afternoon and evening.

.LONG TERM /SATURDAY THROUGH TUESDAY/...Friday`s system quickly
exists to the east and carves out a decent trough over the
Intermountain West. Cool, dry northerly flow aloft develops over
the region over the weekend and upper ridging gradually builds
into the area. This spells a good amount of sunshine along
with somewhat cooler daytime highs and colder nights. The 00Z run
of the GFS shifts the ridge axis further eastward early next week
than its predecessors while the ECMWF solution is closer to the
older GFS runs with keeping it further offshore. Both solutions
suggest several days of dry conditions to close out the month of
October along with seasonable daytime temperatures and chilly
overnight lows. Some frost on the pumpkins is likely. 27

&&

.AVIATION...Northwest flow through today as an upper level ridge builds
into the area. Surface flow is light northerly and offshore. The
air mass is generally dry and stable, but low level fog and low
clouds will be around through this morning. LIFR visibilities
across a swath of the Southwest Interior into central Puget Sound
this morning. Areas of IFR low clouds elsewhere. Fog/low clouds
will clear for VFR cigs early this afternoon. Winds generally
light northerly. JD

KSEA...LIFR cigs with fog this morning is expected to clear around 18z.
Scattered low clouds also around this morning. VFR cigs for the
afternoon. Light northerly winds. JD

&&

.MARINE...High pressure will build into the area today through
Thursday with light offshore flow. A system will move through the
waters Friday into Friday night with SCA level winds for most
waters and a westerly push through the Strait. High pressure
builds back in following the system. JD

&&

.HYDROLOGY...The only reach above flood stage is the Snoqualmie
River near Carnation. It crested around 9 PM Tuesday and will
continue to recede today, falling below flood stage Wednesday
afternoon or evening. The Snohomish River is below flood stage;
there is a chance it could rise to near flood stage Wednesday
afternoon or evening as the crest from the Snoqualmie River
passes. No further flooding is expected for the rest of the week.

Burke

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Dense Fog Advisory until 10 AM PDT this morning for Southwest
     Interior-Tacoma Area.

PZ...None.
&&

$$

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