Weather

358 
fxus66 ksew 071631 
afdsew 


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


Synopsis...a strong upper level ridge and low level offshore flow 
will produce warm and sunny weather for western Washington today and 
Monday. A weak upper level trough and a dissipating frontal system 
will affect the area Monday night through Wednesday 
morning...bringing mainly morning clouds and cooler temperatures. 
The upper level ridge will build back over the area Wednesday 
afternoon warming temperates through through Thursday. 


&& 


Short term...area of stratus formed north of Arlington earlier this 
morning...and with strong northerly gradient has pushed along 
Cascade foothills down toward McCord Air Force base. Sandpoint 
profiler has northerly winds 20-25 knots between 300 and 600 
meters...which help to quickly mix out stratus later this morning. 
Temperature inversion is not very deep and cloud tops are around 020 
mean sea level. Local stratus break out tool shows breakout just after 19z. 


After a warm and sunny Sunday...offshore flow for will continue 
overnight with the thermally induced trough along the coastline. NAM 
and GFS continue to show thermal trough on the coast at 12z 
Monday...leading to another warm day inland on Monday. Gradients go 
onshore Monday afternoon...and marine air should work inland by 
Tuesday morning likely bringing some low cloud. Weak frontal 
system approaches the coastal waters late Monday..but has no 
precipitation associated with it. The main effect will be to lower 
temperatures several degrees on Tuesday and an increase in morning 
cloud cover. Damico 


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...strong upper level ridge remains anchored offshore with 
northwest flow aloft over Washington. Satellite/surface observation this morning reveals 
areas of low clouds across Puget Sound sound/east Puget Sound sound lowlands with 
patchy fog in the Chehalis valley/Hood Canal. Low clouds will 
scatter out late this morning with clear skies expected this 
afternoon. 


Ksea...low clouds will scatter out/push east of the terminal 
17-18z...with clear skies expected this afternoon. Winds will remain 
northerly at 10 to 15 knots. 33 


&& 


Marine...northerly pressure gradients across West Washington today with inverted 
trough along the coast. Winds will increase to 10 to 20 knots across 
the coast and inland waters this afternoon. Northerly winds may 
increase to small craft criteria this evening over the coastal 
waters. Onshore flow will increase on Monday as the inverted trough 
shifts into East Washington. 33 


&& 


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


$$