Weather

010 
fxus66 ksew 070929 
afdsew 


Area forecast discussion 
National Weather Service Seattle Washington 
230 am PDT sun Sep 7 2008 


Synopsis...a strong upper level ridge and low level offshore flow 
will produce warm sunny weather for western Washington today and 
Monday. A weak upper level trough and a dry front will affect the 
area Monday night through Wednesday morning...bringing mainly 
morning clouds and cooler temperatures. Another upper level ridge 
will move over the Wednesday afternoon and Thursday with sunny and 
warmer weather. A weakening front will reach the area Friday. 


&& 


Short term...the strong upper level ridge will dominate the weather 
pattern today and Monday. A surface high has formed overnight over 
southern b.C. As expected. Surface observation show varying degrees of north 
winds and the Sand Point profiler has north 20 knots above 1000 feet. North flow 
is strong enough to prevent very much fog formation. So far...fog 
product satellite imagery doesn't show any areas of fog and the 
stratus along the coast has been dissipating from north to S...and is 
gone north of Cape Elizabeth. However temperature/dewpoint spreads are still 
close enough for some patchy fog to form this morning...but that is 
about all. Warmer maximum temperatures by 2 t0 6 degrees looks fine for today. 


Models remain consistent in shifting back to onshore flow Monday 
afternoon as the upper level ridge falls apart and a weakening cold 
front approaches the area. 500 mb heights are down a bit ahead of 
the upper level trough associated with the front...so should see a 
few degrees air mass cooling. The front shouldn't amount to 
much...just some middle/hi clouds Monday night/Tuesday. However SW 
onshore flow ahead of it should bring in some marine air to the 
interior for areas of morning stratus mainly west of Puget Sound sound 
Tuesday morning. Kam 


Long term...GFS/ECMWF are in fairly good agreement through Saturday 
with the overall pattern. They bring a rather dry upper level low 
down across b.C. And eastern Washington Tuesday night/Wednesday. Main effect 
will be air mass cooling with maximum temperatures slightly below normal. 
Onshore flow persists for continuing morning stratus problems. 
Another upper level ridge builds over the area Wednesday and 
Thursday...but not as strongly as the current ridge. Offshore flow 
is negligible. Finally both models show another weakening cold front 
reaching the area Thursday night/Friday. At this point this looks 
like a repeat of the dry front earlier this week...however this may 
change since the 500 mb flow is stronger. The front may hold 
together better. Kam 


&& 


Aviation...a thermally induced trough along the Washington coast 
will produce a period of offshore flow through tonight. Upper level 
high pressure will remain centered along 130 west with light NE flow 
aloft. The atmosphere will remain dry and stable...except moist near 
the surface in a few sheltered valley locations and the coast. 
Increasing offshore winds should mix out any patchy low clouds/fog 
by 17z...with clear conditions through the evening. The extent of 
morning fog is expected to be much less than previously anticipated. 


Ksea...NE winds are drying out the low levels making it difficult 
for fog to form. There could be some patchy fog near the terminal 
but trends suggest dense fog is unlikely at the terminal. Already 
updated the taf to take the fog out this morning. Dtm 


&& 


Marine...offshore gradients increased to nearly +1 mb through the 
Strait earlier this evening but have since leveled off. The stronger 
GFS kuil-kbli gradient +2.6 mb may not pan out which would have 
implied winds approaching small craft. Will go between the NAM/GFS 
and keep winds in the 10 to 15 knots range in the West Entrance. 
Elsewhere...light northerly wind will pick up this afternoon but should 
remain below small craft. Dtm 


&& 


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


$$ 
Weather.Gov