Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 311603
Area Forecast Discussion
National Weather Service Seattle WA
905 AM PDT TUE MAY 31 2016
.SYNOPSIS...Upper level ridging will move slowly east across
western Washington today bringing mainly clear skies and another
warm day. A marine push will begin tonight and strengthen on
Wednesday as a weak weather system moves across the area. The
system will bring increasing clouds Wednesday and a chance of
showers Wednesday night through Thursday evening. A stronger upper
level ridge will build into the area next weekend giving sunny
skies and much above normal temperatures.
.SHORT TERM...Starting this morning with an upper ridge axis
squarely over western WA with 500 mb heights near 575 dam. In
addition, the UIL-BLI is offshore at -1.1 mb, and SEA-EAT is flat.
These factors will contribute to a warm day. Max temps from
Seattle on south will be at or above 80F, and afternoon seabreezes
along the coast will be confined to within 5-10 miles of the
Upper ridge axis quickly scoots off to the east this evening.
Upper heights will fall from late today through Wednesday night,
and westerly flow aloft will increase. This will drive a marine
push into western Washington starting Wednesday morning, with
low-level onshore flow really picking up on Wednesday afternoon.
Looking for a deep marine layer by Thursday morning. In
combination with strong onshore flow and a weak upper impulse
passing by, should squeeze out orographic showers on windward
mountain slopes and drizzle elsewhere, especially in the Puget
Sound convergence zone.
Upper heights will start to rise modestly on Thu afternoon.
Showers and drizzle will ever so slowly diminish over the course
of Thu afternoon and be finished on Thu evening.Haner
.LONG TERM...Once that ridge sets up...it is not going anywhere for
a few days. As such...temperatures begin to climb once more for the
duration of the weekend. The ridging shifts eastward for the start
of next week. The interpretation of this by the models is...as
usual...divisive. ECMWF likes the idea of some impulses while GFS is
really content to wait until the next upper level low starts to
approach the coast by the middle of next week. Surrounding offices
have bit hard on ECMWF solution...so have tried to adjust pops to
compromise. That said...might be some convective stuff over the
mountains early next week...but nothing for lowlands. Also seeing
potential for lightning from neighbors during this time frame...but
chances for precip during this time look less than stellar...thus a
little too early to speculate whether or not there will be lightning
with rain that has the odds against it in terms of whether it will
happen or not. SMR
.AVIATION...An upper ridge over the pacific northwest will weaken
and shift inland today and tonight. Westerly flow aloft becoming
southwesterly tonight. At the surface, a thermal trough along the
coast this morning will shift over western Washington today and then
into eastern Washington tonight. The air mass is dry and stable with
high clouds at times. Low clouds are expected to develop at the
coast late tonight.
KSEA...High clouds at times. Northerly wind 5-10 knots, becoming
light tonight, and then south 3-6 knots Wednesday morning.
.MARINE....A thermal trough along the coast this morning will shift
over western Washington this afternoon and then into eastern
Washington tonight. Small craft advisory west winds are likely for
the central and eastern Strait of Juan De Fuca beginning tonight and
continuing off and on for much of the week with the onshore flow
pattern. There is also a good chance of a few hours of small
craft advisory northwest winds this evening for the central and
southern inner coastal waters.
Onshore flow will ease and turn more northerly late this week as
another thermal trough builds north along the west coast.
PZ...Small Craft Advisory from 6 PM this evening to 5 AM PDT
Thursday for Central U.S. Waters Strait Of Juan De Fuca-East
Entrance U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory from 5 PM this afternoon to 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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