Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 312251
Area Forecast Discussion
National Weather Service Seattle WA
351 PM PDT TUE MAY 31 2016
.SYNOPSIS...An upper ridge is exiting into eastern Washington
this afternoon. With the departure of high pressure and increasing
westerly flow aloft, a marine push will penetrate into western
Washington on Wednesday. Showers are expected on Thursday morning
due to a deep marine layer and a weak upper level disturbance. A
strong upper level high pressure ridge will start to expand into
western Washington on Thursday night and peak over the weekend,
bringing much above normal temperatures this weekend.
.SHORT TERM...Upper ridge axis over central Washington this
afternoon is exiting to the east. Falling upper heights are
expected tonight with increasing westerly flow aloft. A marine
push will get underway on Wednesday morning, pushing hard into the
I-5 corridor on Wednesday afternoon and evening. This will bring
increasing clouds and the start of a two-day cooling trend.
The marine layer will be quite deep late Wednesday night and on
Thursday. The passage of an upper shortwave early Thursday morning
and the low-level onshore flow will lead to quite a few showers
early Thursday. The shortwave will exit on Thursday afternoon, so
showers will be diminishing Thu PM. Owing to the deep marine
layer, onshore flow and showers, Thursday will be the coolest and
cloudiest day for the remainder of this week.
Strong upper level height rises are expected on Thursday night and
Friday, as a strong upper ridge axis develops over eastern
Washington. Low-level onshore flow will cut off on Friday, setting
the stage for clearing and a rapid warm-up.Haner
.LONG TERM...Friday`s upper ridge axis over eastern Washington
will retrograde slightly into central Washington on Saturday, and
upper heights will continue to rise. 500 mb heights will
eventually peak near 588 dam over western WA on Sat PM, with low-
level offshore flow on Saturday morning. The warming trend will
continue, with warm temps to the coast and interior temps reaching
the upper 80s, possibly near 90F south of OLM.
On Sunday, the upper ridge axis will push back east of the
Cascades. Cooling seabreezes will re-develop at the coast, but
interior temperatures will actually climb a little more. Have
boosted the official forecast high for SEA on Sunday to 85F, but
normal June lapse rates to 850 mb suggest 90+ degree temps are
possible on Sunday.
The upper ridge axis will flatten and weaken early next week, so
cooling onshore flow will strengthen. Would expect marine clouds
pushing inland from the coast on Monday morning. Cooling trend
will continue next Tuesday. The ECMWF is a bit cooler next Tue
than the GFS. Next round of organized precip should hold off until
beyond Day 7. Haner
.AVIATION...Upper level ridge east of the area with southwesterly
flow aloft. Weak system moving by to the north later Wednesday. Air
mass dry and stable with high clouds at times except along the coast
where low clouds are expected Wednesday morning.
KSEA...High clouds at times. Northwest wind 5-10 knots, becoming
light tonight, and then south 4-8 knots Wednesday morning.
.MARINE....A thermal trough over the inland waters will
shift into eastern Washington tonight. Small craft advisory west
winds are expected for the central and eastern Strait of Juan De
Fuca beginning tonight and continuing off and on through at least
early Friday morning with the low level onshore flow pattern. Small
craft advisory northwest winds are also expected this evening for
the inner coastal waters.
Onshore flow will ease and turn more northerly Friday with another
thermal trough builds north along the west coast Saturday. The
thermal trough will shift inland late in the weekend. Felton
PZ...Small Craft Advisory until 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 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
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