Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 191016
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
316 AM PDT Mon Jun 19 2017

.SYNOPSIS...High pressure aloft will prevail for dry and warmer
weather today. A weak cold front will bring a threat of rain to
the region tonight and Tuesday. Expect onshore flow to keep
temperatures near normal Tuesday and Wednesday. Anticipate a
warming trend the latter part of this week.

&&

.SHORT TERM...Overall, a dry and mild day on tap for Western
Washington. Skies cleared late last evening but low clouds have
formed in place overnight. The GOES R fog product shows much of
the lowlands covered this morning. The cloud layer is shallow and
will quickly burn off late this morning and early afternoon. The
air mass is warmer with an upper level ridge over the region.
Afternoon temps will reach the 70s in the interior with a few low
80s away from the sound. Expect highs in the mid 60s along the
coast with onshore flow.

The ridge over the area will flatten on Tuesday as a cold front
moves inland. This front will bring isolated to scattered showers,
mainly during the morning. Onshore flow will increase behind the
front Tuesday afternoon and may see a Puget Sound Convergence
Zone form over the central sound. The stronger push will bring
marine clouds farther inland on Wednesday for cooler conditions -
temps back closer to normal. The weather remains dry on Thursday
as an upper level ridge builds offshore. Pressure gradients are
weaker with less stratus coverage during the morning. Temperatures
will remain seasonal. 33

.LONG TERM...An upper level ridge over the Pac NW will bring dry
and stable weather over the weekend with a slight warming trend
expected. Guidance shows highs reaching the lower to mid 80s
Friday through Sunday, with mid 60s to 70s along the coast. Models
have been waffling on the placement of a closed upper level low
late in the period. Current solutions show the low parked over
B.C. early next week which drop down into WA by midweek. The
result is cooler conditions as heights drop into the 570s. 33

&&

.AVIATION...An upper ridge over the area today will weaken
tonight and Tuesday. Cold front dissipating over
the area on Tuesday. Southwesterly flow aloft. At the
surface, onshore flow will develop today as high pressure
builds offshore and lower pressure moves into Eastern Washington.
The air mass is stable.

Satellite imagery shows low clouds and fog along the
Coast, Strait of Juan De Fuca and along Puget sound from
Snohomish County into Pierce county. Ceilings are mostly below 500
feet with local visibilities less than 1sm. Model cross sections
show the layer is shallow with tops estimated near 1000 feet.
With the shallow layer expect the stratus and fog to burn off over
the interior 17z-19z. Increasing mid and high level clouds this
afternoon and evening.

KSEA...Ceilings below 200 feet with visibilities a mile or less
until around 17z. Fog and stratus burning off quickly after
17z. Increasing mid and high level clouds this afternoon and
evening. Northerly winds 4 to 8 knots.

&&

.MARINE...Onshore flow increasing today with small craft
advisory west winds are expected in the Central and Eastern Strait
this evening.

A weak front will move through the waters on Tuesday. Stronger
onshore flow will develop behind the front Tuesday afternoon and
evening. A gale watch is in effect for the Central and Eastern
Strait Tuesday afternoon and evening. Small craft advisory
westerly Small craft advisory winds are expected over most of the
remainder of the waters late Tuesday.

Moderate onshore flow will prevail on Wednesday with the onshore
flow weakening on Thursday. The low level flow will turn
northerly on Friday with high pressure over southern British
Columbia. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Watch from Tuesday afternoon through Tuesday evening for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 6 PM this evening to noon PDT Tuesday
     for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$

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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