849 
fxus66 kmfr 200507 
afdmfr 


Area forecast discussion 
National Weather Service Medford or 
900 PM PST Wednesday Nov 19 2008 


Discussion...the stable pattern under high pressure will soon break 
down. However it remains stable under the warm front so fogs are 
developing in the western valleys. The fogs should not last the whole 
night. An approaching cold front will mix out stagnant valley air 
late tonight and Thursday morning. It is likely to provide light to 
moderate precipitation to most of our region. Snow levels will 
initially be about 6000 to 6500 feet then fall to 4000 to 5000 
feet Thursday morning behind the front. Thus...an accumulation of 
as much as 3 inches of snow is possible over mountain passes 
Thursday morning. This is not enough to warrant a Winter Weather 
Advisory but there could be hazardous driving conditions Thursday 
morning with a few flurries lingering Thursday afternoon and evening. 


High pressure will briefly build between systems late Thursday 
night into Friday morning with areas of valley fog in southwest 
Oregon and a few patches elsewhere. 


The next upper trough will move into western Canada late Friday 
through Friday night. The associated cold front will be strongest 
for northern Oregon and points northward but sufficiently strong 
for rain to be likely in southwest Oregon and a chance in Siskiyou 
and Klamath counties Friday night into Saturday morning. Snow 
levels are again expected to be around 5000 to 6000 feet for the 
large majority of the event with minimal accumulations...up to 2 
inches in the Cascades. 


High pressure aloft will begin to build in from the west Saturday 
afternoon and persist into Sunday evening. Thus...the main 
weather feature of interest for most of the weekend will be 
valley fog. 


In a bit of a role reversal from the normal model biases...the 
European model (ecmwf) is weaker with the weekend ridge and thus faster in moving 
in the next weather system early next week. 


Given the wide disparities in model solutions...the forecast for 
next week beyond Sunday night reflects a broad brush leaning 
toward the European model (ecmwf) timing and the expectation of an active pattern 
with periods of precipitation. The highest probability for next 
week is that light to moderate snow will create travel issues at 
times over mountain passes including Siskiyou Summit but the lower 
atmosphere mostly remaining mixed will be good news for air 
travelers and at this time none of the weather systems look to be 
especially strong or cold. 


&& 


Aviation...conditions will remain VFR this evening then a cold 
front will reach the coast after midnight. MVFR and local IFR 
conditions associated with the front will spread inland Thursday 
morning but the IFR will be mostly as mountain obscurement. 
The front will weaken east of the Cascades in the afternoon but Post 
frontal showers will maintain obscurations of most of the higher 
terrain in the region including the Cascades and Siskiyous. 


&& 


Mfr watches/warnings/advisories... 
or...air stagnation advisory until 10 PM PST this evening for orz023- 
orz024-orz026-orz029. 


California...none. 


Pacific coastal waters...Small Craft Advisory for winds from 10 PM 
this evening to 4 am PST Thursday for pzz350-pzz356-pzz370- 
pzz376. 
Hazardous seas warning from 10 am Thursday to 4 PM PST Saturday 
for pzz350-pzz356-pzz370-pzz376. 
Gale Warning from 4 am to 10 am PST Thursday for pzz350-pzz356- 
pzz370-pzz376. 
Small Craft Advisory for hazardous seas from 10 PM this evening 
to 10 am PST Thursday for pzz350-pzz356-pzz370-pzz376. 


$$ 


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