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Area forecast discussion 
National Weather Service Seattle Washington 
905 PM PDT Wednesday Oct 15 2008 


Synopsis...a warm front will bring periods of rain across western 
Washington tonight. This first warm front will move northeast 
Thursday morning and a second warm front from a trailing weather 
system will approach coastal waters late Thursday afternoon. The 
cold front from this system will move across the area on Friday. A 
drying trend will take place Saturday through Sunday afternoon as a 
weak upper level ridge moves over the area in between weather 
systems. A stronger Pacific frontal system will arrive on Monday. 


&& 


Short term...warm front rain has moved inland a bit faster than 
planned. Threw in the now wet towel and updated with 100 percent 
probability of precipitation for tonight. Good low level warm advection coupled with the 
nose of a 100+ knot jet streak have supplied the lift needed for the 
rain. In fact there was a nice dry layer below 10000 feet this 
afternoon that was supposed to slow the onset of the rain. That sure 
went poooffff. Latest radar loop seems to indicate the most 
organized rain band is right over Puget Sound sound at 830 PM and is 
rapidly moving east over the Cascades. Coldest cloud tops on infrared 
imagery support this. The warm front is still just offshore so 
should still be some off and on rain the rest of the night. 


Latest infrared imagery shows a decent gap between the surface low near 
49n/130w and our current warm front...and the upstream frontal 
system that is still west of 135w. Dayshift idea of a lull in precipitation 
looks good...and Thursday may end up being just cloudy with only a 
chance of rain for the interior. 18z GFS shows weak but increasing 
warm advection from the next systems warm front after 18z Thursday. 
Chance of rain Thursday afternoon looks fine for the interior...but 
the coast should have likely or better probability of precipitation in the afternoon. Should 
be periods of rain again Thursday night with the best warm advection 
over the north part. GFS remains consistent in bringing the cold 
front across the area on Friday. 


With the cold front just east of the Cascades early Saturday 
morning...the dry Saturday forecast looks pretty good. Even MOS probability of precipitation 
are only at around 10. Should be too soon after the cold front for 
much more than patchy fog Saturday...but with a surface high moving 
briefly over the area Saturday night the best period for areas of 
fog will be Sunday morning. Kam 


Long term...previous discussion from the 335 PM afd...on Sunday 
ridging begins to build over the area as the next frontal system 
approaches our coastal waters. Sunday should begin mostly sunny 
after areas of morning fog but may see some high clouds roll in 
during the afternoon. GFS is slightly faster then the European model (ecmwf)...but a 
stronger and deeper frontal system driven by a strong jet passes to 
our north on Monday. A pool of colder air follows with the upper 
trough and snow levels fall to 3500-4000 feet by Tuesday morning. 
There will be a break before the next system arrives sometime 
Wednesday...but have left chance of rain in the forecast for now. 
Damico 


&& 


Aviation...light warm frontal precipitation has overspread most of western 
Washington...much faster than some computer models were indicating. Ceilings are 
still VFR across most the area but expected areas of MVFR and isolated 
IFR to develop after midnight as the low levels continue to moisten 
up in a stable air mass. Sheltered valleys like kolm stand the best 
chance of IFR ceilings/visible with not much flow at the surface. The flow 
aloft will remain moderate southwesterly tonight. The warm front should lift 
mostly north of the area after 18z Thursday with a break in precipitation over 
much of the area Thursday afternoon. A cold front will bring more rain 
Thursday night with strong SW flow aloft. 


Ksea...S wind 5 knots or less tonight. Rain at times through 18z Thursday 
with a warm front draped over the area. VFR conditions are likely 
to prevail overall with the ceiling in the 3500-6000 feet 
range...however occasional MVFR conditions are possible especially 
12z-16z Thursday morning. Dtm 


&& 


Marine...a warm front will lift across the waters tonight and Thursday. 
Expect solid small craft winds along the coast. Winds at the 
entrances to the Strait and the north interior will rise to marginal 
small craft criteria. The associated cold front will bring another 
round of stronger winds to the waters Thursday night. Gales are not 
expected...but the coastal waters will probably reach 30 knots at 
times. Winds will subside behind the front Friday. 


&& 


Sew watches/warnings/advisories... 
Washington...none. 
Pz...Small Craft Advisory coastal waters...entrances to the Strait... 
Admiralty Inlet...northern inland waters. 


$$ 


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