FXUS66 KMFR 110407
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
805 PM PST THU DEC 10 2009

.SHORT TERM...A WARM FRONT WILL MOVE NORTH AND BRING MAINLY LIGHT 
SNOW TO NORTHERN CALIFORNIA AND SOUTHWESTERN OREGON FRIDAY INTO 
FRIDAY NIGHT WITH A CHANGE OVER TO MIXED RAIN AND SNOW THEN RAIN 
SATURDAY.

GIVEN SPLIT FLOW REGIME AND VERY DRY AIR IN PLACE...PRECIPITATION
AMOUNTS WILL REMAIN FAIRLY LOW WITH THIS SYSTEM. SUBTLETIES IN
THE TIMING...TEMPERATURE FIELD AND PROJECTED SNOW LEVELS YIELD
VERY DIFFERENT OUTCOMES...SO THERE IS SOME UNCERTAINTY IN THE
DETAILS OF THE FORECAST. 

WINTER WEATHER ADVISORY HAVE BEEN ISSUED FOR 1 TO 3 INCHES EXPECTED 
IN LOWER TERRAIN OF CENTRAL AND WESTERN SISKIYOU COUNTY. IN THE 
ROGUE AND ILLINOIS VALLEYS EXPECT SOME LIGHT SNOW...ACCUMULATIONS UP 
TO AN INCH.

ON SATURDAY AND SUNDAY A MORE POTENT LOW WILL IMPACT THE CWA WITH
MORE PRECIPITATION. SNOW LEVELS WILL RANGE BETWEEN 2500
TO 3000 FEET.

.LONG TERM...
MONDAY:
12Z GFS/ECMWF/CANADIAN INDICATE 500 HPA SHORTWAVE RIDGING MONDAY 
AHEAD OF THE NEXT WEATHER SYSTEM.

TUESDAY:
AN UPPER LEVEL TROF WILL PUSH A SURFACE COLD FRONT THROUGH THE 
REGION TUESDAY. WARM AIR ADVECTION AHEAD OF THIS SYSTEM WILL 
INCREASE SNOW LEVELS BETWEEN 4500 TO 5500 FEET.

WEDNESDAY AND THURSDAY:
THE FLOW BECOMES A BIT MORE ZONAL WITH A FLAT RIDGE BUILDING IN FROM 
THE SOUTHEAST. THE GFS CONTINUES THE ZONAL PATTERN WITH WEAK 
SHORTWAVES MOVING THROUGH WHILE THE ECMWF SHOWS A LARGE AMPLITUDE 
500 HPA RIDGE BUILDING OVER THE WEST COAST.

&&

.AVIATION...VFR CONDITIONS WILL LIKELY CONTINUE THROUGH FRIDAY 
MORNING. LIGHT SNOW MAY REDUCE VISIBILITIES OVER NORTHERN CALIFORNIA 
BY FRIDAY MORNING...AND THEN ROGUE VALLEY AND KLAMATH FALLS AREA BY
FRIDAY EVENING. CEILINGS WILL LIKELY DROP TO MVFR BY 18Z FRIDAY
WITH MOUNTAINS OBSCURED AS WELL.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FREEZE WARNING FROM 11 PM THIS EVENING TO 9 AM PST FRIDAY FOR 
     ORZ021-ORZ022.

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

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