Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 232212
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
312 PM PDT Fri Jun 23 2017

.SYNOPSIS...An upper ridge, combined with low level offshore flow,
will give hot and dry conditions to much of the area Saturday
through Sunday. Onshore flow will usher cooler marine air into the
area Sunday night as the upper ridge moves off to the east.
Temperatures will cool to near average for late June early next
week, and the marine air will give late night and morning
cloudiness to the area. No rain is expected over the next week.

&&

.SHORT TERM...Skies remain clear across the region this afternoon.
The air mass has gradually warmed today with temperatures about 5
to 10 degrees higher than they were 24 hours ago. 500 mb heights
are expected to rise to close to 5900 meters this weekend. Warming
and ridging aloft combined with increasing offshore flow and low
level compressional heating will add to the warmth of the
boundary layer this weekend. Afternoon high temperatures will be
close to record levels on Saturday and will likely break records
on Sunday.

The hottest day at the coast is expected Saturday, including
places like Forks and Hoquiam as offshore winds increase. Areas
around the southwest interior and greater Puget Sound area to the
south of Everett will also reach the upper 80s to mid 90s (highest
in the southwest interior). Forecasts generally follow the warmer
third of the mean of raw 2 meter temperatures from the mesoscale
models and GFS MOS and are little changed from previous forecasts.

Models continue to show the thermally induced low shifting inland
over Puget Sound on Sunday with easterly cross Cascade gradients
peaking during the morning to midday. This will bring the hottest
temperatures of the year so far to the I-5 metro areas including
Seattle and Bellevue. Lows Sunday morning will only fall into the
60s in portions of the greater Puget Sound metro areas. Highs
will likely rise to around 90 in Everett and into the lower to mid
90s Seattle and Bremerton southward. A heat advisory remains in
effect for the Seattle-Tacoma- Bellevue metro areas southward to
the southwest interior and east toward the Cascades for midday
Saturday through Sunday evening.

With the heat in the interior on Sunday and the upper ridge moving
off to the east, marine air will spread into the gaps and onto the
coast Sunday night and early Monday and will continue to deepen
into the interior on Monday. Temperatures on Monday are uncertain
with some solutions showing highs only in the lower 70s inland and
others showing mid 80s in the Seattle area and east Puget Sound
lowlands as clouds rapidly burn back to the west during the
morning hours. At this time, the partial marine push scenario is
indicated in the forecasts, and forecasts will be revised once
solutions become more consistent. Albrecht

.LONG TERM...The upper level pattern is forecast to be progressive
over the next week or so with troughing moving into the area early
to mid week and ridging returning later next weekend.

For the Tuesday through Friday period, the forecast will indicate
night and morning clouds with clearing inland during the afternoon
hours. Temperatures are expected to fall to near or slightly below
normal Tuesday or Wednesday then moderate slowly late in the week
as the marine layer deepens and moderates. At this time it appears
that conditions will remain dry for the next week or so. Albrecht

&&

.AVIATION...An upper level ridge will remain over the region for
contd NW flow aloft. NLY low level flow will become offshore or
easterly tonight, continuing thru Saturday. VFR conditions will
prevail.

KSEA...VFR. Winds will be northerly 7-14 knots, strongest thru
early this evening.

&&

.MARINE...The flow will become offshore or northeasterly tonight
due to a thermally induced trough of low pressure becoming
established just off the coast. Expect offshore flow to persist
during much of this weekend.

The thermally induced trough of low pressure will shift east of
the Cascades Sunday afternoon. This will cause the flow to become
onshore and then strengthen Sunday night, resulting in gale force
winds over parts of the Strait of Juan de Fuca. Strong onshore
flow will prevail Monday before weakening some on Tuesday.

&&

.FIRE WEATHER...Hot and dry conditions this weekend will be somewhat
favorable for grass and brush fires over the lowlands. On both
Saturday and Sunday, minimum RH values will be below 20% in the
afternoons. Some recovery will occur each night. Moderate northeast
wind at times will mean the weather parameters approach red flag
thresholds each afternoon. However, fuel moisture is generally too
high to give much of a threat of explosive fire development. In
addition, snow still covers much of the terrain above 4000 feet in
the mountains. The exception is so-called "fine fuels," grass and
brush, in the lowlands, which has dried considerably in recent days.
Favored areas for brush fires, such as along highways, will have
some risk of fire this weekend. Burke

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Heat Advisory from noon Saturday to 9 PM PDT Sunday for Bellevue
     and Vicinity-Bremerton and Vicinity-East Puget Sound
     Lowlands-Hood Canal Area-Seattle and Vicinity-Southwest
     Interior-Tacoma Area.

PZ...Small Craft Advisory until 10 PM PDT this evening for Coastal
     Waters From James Island To Point Grenville Out 10 Nm.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html


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