Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 140343
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
843 PM PDT Mon Aug 13 2018

.SYNOPSIS...An upper ridge will produce dry and warm weather the
next couple of days. It will also be smoky at times. Onshore flow
will develop later Wednesday. This will cool highs back to near
normal Thursday and Friday. High pressure aloft will rebuild over
the area next weekend for a return warmer weather.

&&

.SHORT TERM...An upper ridge will be over the area through
Wednesday for dry weather. Weak offshore flow night and morning
hours will turn light onshore in the afternoon as a thermal
trough meanders diurnally between the coast and the interior.
Highs will be above normal but all the smoke will put a damper on
temperatures. Highs will cool around 10 degrees Wednesday at the
coast as onshore flow starts to develop.

The upper ridge will shift inland Wednesday night and Thursday
with a weak upper trough moving to the coast. There will be a
corresponding increase in low level onshore flow. A marine push
will bring some low clouds Thursday morning and cool highs back
to near normal for the interior on Thursday.

Speaking of smoke...smoke from fires to the north and east should
continue to affect the region through at least Tuesday with
visibilities reduced at times. There could also be air quality
concerns on Tuesday and perhaps into Wednesday. Schneider

.LONG TERM...Previous discussion...Models remain consistent with
a weak upper level trough moving through the area Thursday bringing
temperatures back down to near normal with mid to upper 70s
expected in the interior lowlands....mid to upper 60s along the
coast. There looks to be a little bit of lingering influence from
this system on temps into Friday as highs do not look to change
much.

Late Friday afternoon will see upper level ridging intensifying over
the Pacific and as such...this feature`s influence will make its way
into W WA...so...of course...this means a return to warming
conditions and yet another potential run at 90 degrees. SMR

&&

.AVIATION...An upper ridge will be over the area tonight and
Tuesday with northerly flow aloft becoming easterly. At the
surface, light offshore flow tonight and Tuesday morning will
become light onshore Tuesday afternoon as a weak thermal trough
along the coast shifts over the interior. The air mass is dry and
stable. Smoke will continue to cover the area with visibilities
3-5 miles at times. There might be some patchy low clouds and fog
Tuesday morning but it should be pretty limited if there is any at
all.

KSEA...Clear. Visibilities 3-5 miles in smoke at times. Ceilings
3500-4000 feet are possible at times from thicker smoke.
Northerly wind 5-10 knots. Schneider

&&

.MARINE...A weak thermal trough will diurnally meander from the
coast to the inland waters through early Wednesday with light
offshore flow night and morning hours and weak onshore flow in the
afternoon. Marginal small craft advisory strength northwest winds
for the inner Coastal Waters should ease this evening.

Stronger onshore flow will develop later Wednesday and continue
through Saturday. Small craft advisory strength west winds are
likely each night for the Central and Eastern Strait of Juan de
Fuca. There will also be small craft advisory strength northwest
winds at times for the outer Coastal Waters. Schneider

&&

.FIRE WEATHER...The mid-levels (850-700 mb layer) will become dry
and unstable over the Cascades on Tuesday PM. Forecast models point
to development of an area of mid-level Haines 6 conditions over the
Cascades. However, the thick regional scale smoke --- which
models do not account for --- will keep the near-surface air mass
more stable. Will therefore use discretion and avoid issuance of a
Red Flag Warning. However if the smoke unexpectedly clears out
and solar insolation picks up on Tuesday afternoon, existing fires
could easily respond to the dry and unstable mid-level air mass.
Haner

&&

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

&&

$$

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