Weather

846 
fxus66 ksew 070422 
afdsew 


Area forecast discussion 
National Weather Service Seattle Washington 
900 PM PDT Sat Sep 6 2008 


Synopsis...an upper level ridge continues to bring fair weather to 
the Pacific northwest. A thermally induced trough of low pressure 
will build up the Washington coast Sunday turning the surface flow 
offshore. Sunday and Monday will be warmer with temperatures running 
above seasonal normals. Temperatures will cool as a dissipating 
weather system brushes the area Monday night and Tuesday. High 
pressure with offshore flow will bring warmer temperatures Wednesday 
and Thursday. 


&& 


Short term...pretty clear skies over the area with only a few 
strato-cumulus here and there...mainly over the mountains. Northerly 
flow showing up well on the satellite pictures with the coastal stratus 
heading south. Gradients offshore over western Washington this 
evening which will help limit stratus formation. However with 
dewpoints relatively high and longer nights...may end up with some 
fog formation in areas where the wind dies off enough. Whatever fog 
develops will burn off fairly quickly Sunday revealing another sunny 
and mild day. 


A dissipating front will approach the coastal waters Monday 
afternoon...and the flow will turn onshore on the coast Monday 
afternoon as the thermal trough shift inland. GFS and NAM show the 
push trending slightly later in the day then previous model runs. 
Weak northwest push will move clouds in Monday night...and heights 
will drop further on Tuesday as a shortwave trough digs into 
southern British Columbia. 


Long term...from previous discussion...still no quantitative precipitation forecast forecasted 
through the entire forecast period...as the trough quickly moves 
into the Idaho/Montana border by Wednesday morning...and the ridge begins to build 
again around 140w. Gradients briefly go offshore again Wednesday 
before the next frontal system attempts to break down the ridge on 
Thursday...likely resulting in only some high cloud cover in the 
late afternoon/evening. Weak frontal system washes out to our east 
on Friday...and the ridge builds back in on Saturday. Damico 


&& 


Aviation...a ridge of high pressure will persist along 130w through 
Sunday. Light NE flow aloft and stable. Air mass dry...except moist below 
1k feet with areas of low stratus and fog forming later tonight. Many 
of the terminals will likely see a 2-4 hour period of stratus and 
fog Sunday morning...and some visibilities will likely be 1/2sm or 
less in fog. With increasing offshore gradients Sunday 
morning...clouds/stratus should mix out by 17z. 


Ksea...low stratus and fog will likely develop in the valleys east of 
I-5 late tonight...likely reaching the terminal by 12z-13z. Low 
level moisture will rapidly evaporate after 17z. Visibilities 
between 14z and 17z may occasionally drop below 1/2sm fog. Dtm 


&& 


Marine...offshore flow through Sunday. The NAM Ely gradient is 
currently running way too low for kuil-kbli...the GFS looks much 
better with -2.3 mb by 12z. This should result in stronger east winds 
at the West Entrance...possibly approaching small craft early Sunday 
morning. North/NE wind over the interior will also pick up on 
Sunday...but should remain below 20 knots through the afternoon. Dtm 


&& 


Sew watches/warnings/advisories... 
Washington...none. 
Pz...none. 


$$ 
Weather.Gov