Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 180427
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
900 PM PDT Mon Apr 17 2017

.SYNOPSIS...A front will spread rain over the area this evening.
Another front will bring more rain Tuesday, and another one will
affect mainly western areas Wednesday. After showers Thursday,
Friday looks dry under a ridge. Weak weather systems will arrive
Saturday and Sunday, with a stronger system possible Monday.

&&

.SHORT TERM...A broad deep upper low centered just north of 40N
outside of 140W will shift slowly eastward over the next couple of
days. A series of short waves embedded in moist southwest flow will
bring rain at times to Wrn Wa. One wave moved through earlier this
evening bringing mostly light amounts. Heaviest rainfall tonight
will be over Oregon as shown by models and currently depicted by
strong radar reflectivity over NW Oregon. The lull in precipitation
overnight will give way to additional rain at times Tuesday as
another short waves lifts across the area. An isolated thunderstorm
could pop up over the Cascades in the afternoon.

Another lull or break in precipitation is expected Tuesday night
before the main frontal band moves into the area with rain at times
on Wednesday. The flow becomes southerly ahead of this system so
high temperatures may reach the upper 50s or even low 60s Tuesday or
Wednesday ahead of the upper trough. The trough will bring showers,
cooler temperatures, and an unstable air mass to the area Thursday.
A few thunderstorms could develop as the upper low and cold pool
aloft moves through the region. Mercer

.LONG TERM...Previous discussion...An upper ridge will build
offshore Thursday night, then on Friday it will move directly over
Western Washington. This will give a dry day Friday with at least
some sun, and highs in the 60s. A weak system will move through the
region on Saturday, with an even weaker one Sunday. These will bring
clouds and a chance of rain. A somewhat stronger system will arrive
Monday. The Euro and GFS models are in rough agreement about this
sequence of events. Burke

&&

.AVIATION...A frontal system will move through the area tonight.
Another front will affect the area on Tuesday. At the surface,
southeasterly flow will prevail. The air mass is stable but will
become unstable on Tuesday. Ceilings could dip a little lower in
steadier rain tonight and Tuesday as rain bands move through and the
mountains should be obscured at times in clouds and precip.


KSEA...Current 03z TAF looks fine, no updates expected and no big
changes for the 06Z forecast are likely.

&&

.MARINE...A series of fronts will move through the waters over the
next few days. This will bring off and on small craft advisory winds
to the normal breezier spots. High pressure will build over the
waters Thursday night with offshore flow developing on Friday.
Another frontal system will reach the area on Saturday.

&&

.HYDROLOGY...River flooding is unlikely over the next seven days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory for the coastal waters, east entrance
     Strait of Juan de Fuca, northern inland waters, Admiralty Inlet.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html



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