FXUS66 KMFR 220453
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
853 PM PST MON DEC 21 2009

.DISCUSSION...AN UPDATE IS NOT NECESSARY. THE COLD FRONT IS ABOUT
TO EXIT EASTERN PORTIONS OF LAKE AND MODOC COUNTIES. THERE IS A
BIT OF A LULL IN POST-FRONTAL SHOWERS AND SNOW SHOWERS BUT THE
AIR MASS IS COLD AND MOIST. SHOWER COVERAGE WILL GET A BOOST AFTER
MIDNIGHT FROM A SHORTWAVE ARRIVING FROM THE NORTHWEST WITH
ACTIVITY FOCUSED AROUND 4 AM. SHOWERS WILL BE MOST NUMEROUS IN THE
HIGHER TERRAIN AND LOCATIONS WHERE NORTHWEST WINDS ARE
UPSLOPE...SUCH AS NEAR SISKIYOU SUMMIT. SNOW LEVELS NEAR 2500 TO
3000 FEET AT THE MOMENT WILL FALL TO NEAR 1500 FEET OVERNIGHT.
SHOWERS WILL TAPER OFF AFTER 10 AM...AND END COMPLETELY AROUND 4
PM TUESDAY AS A HIGH PRESSURE RIDGE BUILDS OVER THE EASTERN PACIFIC.
THE AMOUNT OF SNOW PRESENTLY FORECAST LOOKS IN-LINE WITH AROUND AN
INCH POSSIBLE DOWN TO 1500 FEET...ADVISORY LEVEL AMOUNTS OF 3 TO
8 INCHES IN THE HIGHER TERRAIN OF THE CASCADES AND SISKIYOUS AND
UP TO 3 INCHES ON THE EAST SIDE.

&&

.AVIATION...WIDESPREAD MVFR CIGS WITH AREAS OF IFR IN RAIN
AND SNOW SHOWERS OVERNIGHT THROUGH TUESDAY MORNING WITH MOUNTAIN
TOPS OBSCURED.

&&

.PREV DISCUSSION... /ISSUED 328 PM PST MON DEC 21 2009/ 

DISCUSSION...THE COLD FRONT IS MOVING ACROSS THE FORECAST AREA
THIS AFTERNOON. PRECIPITATION AT THE COAST RANGED FROM 1 TO 2
INCHES WITH ABOUT 0.10 INCH HERE AT MEDFORD AIRPORT. SNOW LEVEL
WILL QUICKLY LOWER BEHIND THE FRONT TO AROUND 3500 FEET THIS
EVENING THEN DOWN TO 2000 FEET...WITH 1500 FEET FURTHER NORTH IN
DOUGLAS COUNTY. HOWEVER PRECIPITATION IS EXPECTED DECREASE RAPIDLY
BEHIND THE FRONT. THE UPPER LEVEL TROUGH BEHIND THE FRONT WILL
MOVE THROUGH TONIGHT WITH UNSTABLE COLD AIR ALOFT. NORTHWEST FLOW
WILL PROVIDE FOR UPSLOPE ENHANCEMENT ACROSS THE CASCADES AND
SISKIYOUS AND HAVE ISSUED A WINTER WEATHER ADVISORY FOR THOSE
ZONES WITH THE HEAVIER ACCUMULATION AT THE HIGHER END OF THE
ZONES. AS THE FRONT MOVES EAST OF THE CASCADES...THE NAM12
INDICATES A BAND OF HEAVIER PRECIPITATION FROM EAST SISKIYOU
COUNTY NORTHEASTWARD INTO LAKE COUNTY. COMBINED WITH LOWERING SNOW
LEVEL AND UPSLOPE FLOW INTO THE WARNERS...HAVE ISSUED AN ADVISORY
FOR THE EAST SIDE ABOVE 5000 FEET. HAVE DECIDED NOT TO INCLUDE THE
KLAMATH BASIN IN THE ADVISORY DUE TO POSSIBLE DOWNSLOPE FLOW FROM
WEST- NORTHWEST WINDS. THE WESTERN SISKIYOU COUNTY HAS SEEN
CONSTANT PRECIPITATION TODAY BUT WITH HIGH SNOW LEVEL. HAVE
CONTINUED WITH THE CURRENT ADVISORY AS COLDER AIR IS NOW FILTERING
INTO THE AREA.

SHOWERS WILL LINGER ACROSS THE HIGHER TERRAIN INTO TUESDAY
MORNING...TAPERING OFF TUESDAY AFTERNOON AS WESTERLY FLOW
DECREASES. LATEST MODEL RUN IS STILL CONSISTENT WITH A RIDGE
BUILDING INTO THE AREA FROM WEDNESDAY THROUGH CHRISTMAS. THIS WILL
PRESENT AVIATION CONCERN WITH LOW CEILINGS AND POOR
VISIBILITY...AND COLDER DAY TIME TEMPERATURES DUE TO PERSISTENT
FOG. FOR NEXT WEEKEND...HAVE LEANED TOWARD THE ENSEMBLE MEANS
SHOWING A SPLITTING TROUGH WITH MOST IF NOT ALL OF THE ENERGY
HEADING INTO CALIFORNIA.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL 10 AM PST TUESDAY FOR ORZ027-
     ORZ028-ORZ030-ORZ031.

CA...WINTER WEATHER ADVISORY UNTIL 10 AM PST TUESDAY FOR CAZ080-
     CAZ085.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS 
     UNTIL 4 AM PST WEDNESDAY FOR PZZ350-PZZ356-PZZ370-PZZ376.
     SMALL CRAFT ADVISORY FOR WINDS UNTIL 10 AM PST TUESDAY FOR 
     PZZ370-PZZ376.

$$

DW