731 
fxus66 kmfr 201650 
afdmfr 


Area forecast discussion 
National Weather Service Medford or 
850 am PST Thursday Nov 20 2008 


Discussion...the marine forecast has been updated to scale the gale 
back to Small Craft Advisory conditions today as the fast moving 
cold front has moved inland and will reach the Cascades in about 
an hour. The zone forecast will not be updated this morning. A 
Post frontal shortwave trough offshore from northern and central 
Oregon will generate showers late this morning through this 
evening. Showers will be most numerous north of our region but 
westerly flow will favor the development of showers and snow 
flurries for eastern Douglas County and the southern Oregon 
Cascades. Snow levels are presently above the Cascade Mountain 
passes but they will drop to around 4000 to 4500 feet behind the 
front with the flurries creating as much as three inches of 
accumulation...but mainly an inch or less. 


The next front looks to have similar characteristics to the 
current front. It is forecast to move across Friday night through 
Saturday morning. 


The recently arrived 12z GFS data has trended stronger with 
ridging behind the Friday night system over the weekend into 
Monday and also noticeably weaker with the first couple 
disturbances next week. The 00z European model (ecmwf) supports this solution. 
Thus...the outlook is still favorable for pre-Holiday travel... 
valley fog may be the only weather issue. But there is significant 
uncertainty about conditions beginning Thanksgiving day itself. 




&& 


Aviation...a cold front will create mountain obscurations with areas 
of MVFR and local IFR then weaken east of the Cascades late this 
afternoon. Areas of IFR in valley fog and low ceilings are expected to 
develop overnight tonight and persist into Friday morning. 


&& 


Previous discussion... /issued 309 am PST Thursday Nov 20 2008/ 


Short term...a cold front located just offshore is moving 
towards the coast and will move inland across the area morning. 
Winds along the coast have increased to around 10 to 20 miles per hour with 
gusts up to 35 miles per hour with a few stations along the coast reporting 
light rain. This front will bring light rain and snow to the 
area with some moderate rainfall amounts around a half to three 
quarters inch expected near the coast. As the upper level trough 
moves inland during the afternoon...onshore flow with unstable 
cooler air aloft will keep a showery pattern over the area with 
snow levels lowering from around 6000 feet to near 4000 to 5000 
feet in cold air advection. Showers will be light with best 
activity in areas of favorable upslope flow such as along the 
western slopes of the Cascades. The southern Oregon Cascades are 
expected to receive 1 to 3 inches of snow today with locally 
higher amounts from this system. Showers will taper off during 
the evening as the trough shifts eastward. 


Some breezy and gusty winds are also expected today as the front 
and upper trough pass over the region...especially for locations 
along the coast...over the mountains and for areas east of the 
Cascades. Inland...winds have increased over higher terrain above 
4000 feet with gusts being reported of around 20 to 30 miles per hour. Expect 
winds to increase during the morning and remain breezy and gusty 
over higher terrain through the afternoon. Winds will diminish 
with the trough passage this evening. 


A brief upper level ridge develops Friday morning ahead of the 
next front. Areas of valley fog is expected to develop Friday 
morning...mainly west of the Cascades. This ridge will quickly shift 
east as the cold front moves into the coast Friday evening and 
inland Friday night. This system will bring another round of light 
rain with some higher elevation snow above 5000 feet. 




&& 


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


California...none. 


Pacific coastal waters...Small Craft Advisory for winds until 11 am 
PST this morning for pzz356-pzz376. 
Small Craft Advisory for hazardous seas until 10 am PST Sunday 
for pzz350-pzz356-pzz370-pzz376. 
Small Craft Advisory for winds until 2 PM PST this afternoon for 
pzz350-pzz370. 


$$ 


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