Scientific Forecaster Discussion
fxus66 ksew 262248
Area forecast discussion
National Weather Service Seattle Washington
348 PM PDT Mon Jun 26 2017
Synopsis...onshore flow and a typical pattern of night and morning
clouds, afternoon sunshine and near normal temperatures for the
upcoming work week. An upper level trough will move through the area
over the weekend bringing a slight chance of showers to parts of
Short term...marine stratus has burned off for all but the central
Washington coast/Grays Harbor area this afternoon. Otherwise, mid
and high level clouds continue to stream into the area in the
southwesterly flow aloft resulting in partly to mostly sunny skies
this afternoon and evening. Onshore flow will bring another round of
marine stratus tonight, with a bit more coverage into Tuesday
morning than last night. The overall pattern of late night/morning
clouds, afternoon clearing and near normal temperatures will remain
in place through Thursday. An upper level ridge offshore will begin
to build into the Wednesday night and Thursday with ongoing low
level onshore flow. The building ridge will help temperatures rise a
bit Thursday over Wednesday, but the onshore flow will keep that
warming in check with temperatures reaching into the mid to upper
70s throughout the interior and upper 60s along the coast.
Long term...medium range models models remain in good agreement
through Friday, showing the upper ridge axis overhead around midday
Friday. This will make it the warmest day of the week, however low
level onshore flow and morning clouds will continue to limit the
warming. Temperatures will rise into the low to mid 80s through
parts of the interior, and remain in the mid to upper 60s along the
coast and Strait. Models still begin to differ on the details
Saturday Onward. The European model (ecmwf) and Canadian models continue to be a
little more aggressive with a system moving from the Gulf of Alaska
into British Columbia Saturday, while the GFS continues to be much
weaker with this system. The GFS continues to keep the area dry
through Sunday while the European model (ecmwf) and Canadian bring a chance of
showers to western Washington late Saturday night into Sunday. For
now the forecast leans towards the majority forecast, with a slight
chance of showers Saturday night through Monday - mainly for the
northern portion of the forecast area. Highs will cool back down to
near normal, as the fridays upper level ridge shifts to the east
and low level onshore flow stays in place into early next week.
Aviation...a weak upper level trof centered over western Canada
will continue moving east. West flow aloft will become light northwest late
tonight. Strong low level onshore flow will weaken overnight.
Weakly unstable air mass above the marine layer will stabilize this
evening. The tstm threat should stay east of the Cascade crest.
Meanwhile, expect areas of MVFR cigs over the coast to become wdsprd
this evening before overspreading much of the interior lowlands
Ksea...expect MVFR cigs to return late tonight or after 2 am PDT.
Winds will be south or southwest 5-13 knots, strongest this
afternoon thru early evening.
high pres offshore with lower pres east of the Cascades will result in
onshore flow of varying strength this week.
Pz...Gale Warning until midnight PDT tonight for central Strait of
Juan de Fuca-East Entrance Strait of Juan de Fuca.
Small craft advisories are in effect for parts of the coastal
waters, West Entrance to the Strait of Juan de Fuca, and Admiralty