Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 200306

Area Forecast Discussion
National Weather Service Seattle WA
806 PM PDT Thu Apr 19 2018

.SYNOPSIS...An upper ridge over the area will bring dry weather
into Friday. A frontal system will move quickly across the area
Friday night, followed by showers and sun breaks on Saturday. A
stronger upper ridge has the potential to bring the longest stretch
of dry weather this month beginning Sunday and continuing into the
middle of next week.


.SHORT TERM...An upper ridge remains the dominant weather feature
over W WA this evening and is expected to remain so at least into
Friday afternoon. Models continue to bring a quick moving frontal
system through the area...although most current run (18Z) GFS is
upping the timing some with the front making it to the coast by mid-
afternoon Friday and starting to spill into the remainder of the
area by late afternoon/early evening. Given that this is faster than
previous solutions from both the GFS and ECMWF...would be nice to
see current ECMWF before biting on to this new...faster GFS
solution...but system upgrade from earlier in the day making that
problematic at best. Inherited forecast does indeed bite on to this
faster solution. Looking at the 00Z continues to favor
the slower solutions favored by most of the previous runs. May end
up updating forecast this evening to gear back more toward this
slower solution.

Once the front is through the associated upper level
further south than in previous runs...will keep showers in the
forecast for much of the area into Saturday morning before starting
to taper off during the afternoon. By Saturday night...conditions
look to dry out as upper level ridging builds over the Pacific
making for a dry Sunday.  SMR

.LONG TERM...From Previous Discussion...The Monday through Thursday
period is looking largely dry with high pressure aloft in control.
Highs will be above normal - mostly in the 60s although a few lower
70s are possible around Tuesday. Schneider


.AVIATION...High pressure aloft will weaken tonight and slowly
shift east through Friday. A surface front and associated upper
trough will push through Western Washington at some point on
Friday...most likely Friday night. Light southerly flow aloft will
become strong southwesterly flow Friday afternoon and evening.
Westerly flow aloft weakens by Saturday morning as split flow aloft
develops. Air mass stable and somewhat moist above 5,000 ft. Lower
level moisture increases Friday evening. Dry through Friday, then
rain reaching the coast by late Friday afternoon or early evening
and pushes into the interior Friday night. VFR conditions except
patchy MVFR possible early Friday morning.

KSEA...Northwest 6 to 10 kt easing to 4 to 6 kt by midnight, then
switching to south-southwesterly 5 to 8 kt Friday morning. Mostly
VFR through Friday with sct-bkn clouds around 5k ft and above 12k
ft. Brief MVFR possible around 2500 ft late tonight/Friday
morning. dtm


.MARINE...Surface high pressure offshore will continue to move
eastward and is expected to be east of the Cascades after midnight.
Onshore flow will gradually increase with small craft winds in the
central and eastern Strait tonight. A lull in winds late Friday,
then a front brings more widespread small craft winds to most of the
waters Friday night and Saturday, except possible gales in the
central and eastern Strait. Will await incoming 00Z data before
making a decision on additional headlines for this time period. Any
additional headlines likely to come with the early morning forecast
package. Lighter flow develops Sunday through Tuesday.


PZ...Small Craft Advisory until 3 AM PDT Friday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.


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