219 
fxus66 kmfr 211058 
afdmfr 


Area forecast discussion 
National Weather Service Medford or 
258 am PST Friday Nov 21 2008 


Short term...a weak ridge today will be followed by another cold 
front moving into the region Friday evening and overnight. Then a 
ridge develops over the pacnw Sunday ahead of a deepening trough. 


Tonight..behind a cold front skies are clearing with valley fog 
developing in many west side valleys early this morning. Also high 
clouds over areas east of the Cascades are clearing and expect 
some patchy fog to develop this morning in east side valleys. 
Fog is expected to clear out of most valleys by morning with some 
lingering low clouds possible in the rogue and Illinois valleys 
into the afternoon. 


The NAM...GFS...and European model (ecmwf) are all in fairly good agreement with 
the next front. Models are showing a cold front moving towards the 
Oregon coast this evening with light rain beginning along the 
coast during the evening and spreading inland overnight. Then 
Saturday morning as the front moves east and an upper trough is 
over the region...expect light showers over the area...with showers 
diminishing in the afternoon as the system shifts east. 
Overall...this system appears weaker than the last front. 
Precipitation is expected to be light with a quarter of an inch or 
less over for areas from the Cascades westward in Oregon with 
generally amounts of a few hundredths in other areas. Snow will 
mainly be limited to elevations above 5000 to 5500 feet with a 
light snow accumulations of an around an inch in the Cascades. Winds 
also will be lighter. Expect some south winds of 15 to 25 miles per hour 
along the coast and gusts of 20 to 30 miles per hour over higher terrain 
ahead of the frontal passage. 




&& 


Aviation...coast...VFR with isolated IFR in fog and low ceilings 
early this morning becoming VFR in the late morning. Inland...VFR 
with IFR in valley fog and low ceilings mainly for valleys west of 
the Cascades with some patchy fog possible in the Klamath basin 
early this morning. West side valley fog will gradually lift and 
clear during the late morning and early afternoon becoming VFR. 


Then...Sunday expect high pressure to build over the area with 
clearing skies except for morning valley fog for valleys west of 
the Cascades. 


&& 


Previous discussion... /issued 830 PM PST Thursday Nov 20 2008/ 


High pressure should be the dominant feature early next week with 
cooler temperatures and decreased cloud cover except for night and 
morning valley fog. 


The next trough of interest is now expected to close off and drop 
southward over the offshore waters. This will lead to a split flow 
aloft with the Pacific northwest having the weaker northern branch 
overhead. This should lead to the arrival of a weak front Tuesday 
which will stir up the atmosphere and provide a slight chance to 
chance of precipitation west of the Cascades...mainly north of the 
Umpqua Divide. Both models indicate weak ridging Wednesday and 
another trough in the Gulf of Alaska. 


There is significant uncertainty about conditions beginning 
Thanksgiving day itself. The models have returned to their usual 
biases...which means I would lean with a slower solution than the 
GFS but will be watching for the arrival of a cold front sometime 
toward the end of the week...probably not any earlier than Friday. 
Given the disparity in model solutions...I will include slight chance 
probability of precipitation on Thursday and Thursday night for now as a hedge. 


&& 


Mfr watches/warnings/advisories... 
or...none. 


California...none. 


Pacific coastal waters...Small Craft Advisory for winds from 4 PM 
this afternoon to 4 am PST Saturday for pzz350-pzz356- 
pzz370-pzz376. 
Small Craft Advisory for hazardous seas until 10 am PST Sunday 
for pzz350-pzz356-pzz370-pzz376. 


$$ 


Cirrocumulus