FXUS66 KSTO 142303
AFDSTO

AREA FORECAST DISCUSSION 
NATIONAL WEATHER SERVICE SACRAMENTO CA
300 PM PST MON DEC 14 2009

.DISCUSSION
MAIN CHALLENGE FOR THIS AFTERNOONS FORECAST IS SNOW AMOUNTS OVER 
NORTHERN MOUNTAINS TONIGHT INTO TOMORROW AND FOR NORTHERN SIERRA 
NEVADA LATE TONIGHT INTO WEDNESDAY. MAIN CHALLENGE WILL BE RISING 
SNOW LEVELS WITH THIS STORM SYSTEM.

TONIGHT...OVERALL...LOOKS LIKE MODELS HAVE SLOWED DOWN A BIT WITH 
THE ARRIVAL OF MOISTURE. GOOD AGREEMENT AT THIS TIME THAT MOISTURE 
WILL START IN ZONES 13 AND 14 AFTER MIDNIGHT TONIGHT. DOESN'T APPEAR 
TO BE TOO MUCH COLD AIR TRAPPED IN VALLEY IN THIS AREA BUT 
TEMPERATURES ARE COLD ENOUGH FOR SNOW DOWN TO AROUND 4000 FEET. SNOW 
WILL CONTINUE THROUGH THE NIGHT AND ENOUGH TO HOIST UP A SNOW 
ADVISORY. HEAVIER AMOUNTS WILL OCCUR AT HIGHER ELEVATIONS AND WILL 
HAVE THIS WORDING IN THE WINTER WEATHER ADVISORY. 

TUESDAY...PLUME OF MOISTURE WORKS SOUTHWARD FROM NORTHERN ZONES INTO 
NORTHERN VALLEY. HAVE BACKED OFF OF POPS A BIT IN CENTRAL VALLEY FOR 
A LATER ARRIVAL OF SNOW. GOOD SOUTHERLY FETCH AT LOWER LEVELS WILL 
CONTINUE UP INTO ZONE 13 CREATING A GOOD UPSLOPE EFFECT THERE. 
COUNTING ON SNOW LEVELS TO START RISING TO HOLD OFF ON 
ACCUMULATIONS...BUT LATER SHIFTS WILL HAVE TO WATCH IN CASE IT 
DOESN'T COOL QUICK ENOUGH AND ACCUMULATIONS GET HEAVIER. WILL ALSO 
START A WINTER STORM WARNING FOR HEAVY SNOW IN ZONE 68 TUESDAY 
MORNING AS MOISTURE STARTS WORKING INTO NORTHERN PORTIONS OF THAT 
ZONE. 

TUESDAY NIGHT INTO WEDNESDAY...MAIN ENERGY FROM THE SYSTEM PULLS 
ACROSS THE AREA. STABILITY NOT VERY IMPRESSIVE WITH THIS STORM AND 
TEMPERATURES WILL BE RISING...SO NOT EXPECTING SNOW RATIOS TO BE 
THAT HIGH OVER SIERRA BUT STILL ENOUGH PURE MOISTURE TO GET 1 TO 2 
FEET BY WEDNESDAY FOR THIS SYSTEM. THIS WILL RESULT IN FAIRLY HIGH 
SNOW RATES AT TIMES FOR HAZARDOUS TRAVEL CONDITIONS AT TIMES. 

WEDNESDAY NIGHT INTO THURSDAY STORMS SYSTEM PULLS OUT OF THE AREA 
SLOWLY FOR DECREASING POPS. RASCH

&&

.EXTENDED DISCUSSION (FRIDAY THROUGH MONDAY)...EXTENDED MODELS ARE 
CONTINUING TO HAVE SOME ISSUES IN THE FRIDAY THROUGH MONDAY 
TIMEFRAME.  IT APPEARS THAT HIGH PRESSURE WILL BUILD BACK OVER THE 
REGION ON FRIDAY...AND MAY REMAIN IN PLACE THROUGH THE WEEKEND.  THE 
ECMWF AND CANADIAN BOTH SUGGEST THIS...KEEPING ANY PRECIPITATION 
LIMITED TO THE FAR NORTHWESTERN CORNER OF THE STATE.  HOWEVER...THE 
GFS IS TRYING TO BRING ANOTHER COOL AND WET SYSTEM INTO NORTHERN 
CALIFORNIA FRIDAY NIGHT AND FOR THE WEEKEND.  AT THIS POINT IN 
TIME...HAVE LEANED MORE TOWARDS THE ECMWF AND CANADIAN...BUT HAVE 
LEFT A SLIGHT CHANCE FOR THE MOUNTAINS...AS THINGS MAY COME INTO 
BETTER ALIGNMENT LATER THIS WEEK.

&&

.AVIATION...
CIGS/VISBYS SLOWLY IMPROVING ACROSS THE AREA THOUGH SOME LOW CLOUDS 
STILL EVIDENT ON VISIBLE SATELLITE ACROSS THE NORTHERN SACRAMENTO 
VALLEY. HIGH CLOUDS STARTING TO SPREAD ACROSS NORTHERN CALIFORNIA IN 
ADVANCE OF THE NEXT PACIFIC STORM SYSTEM. EXPECT PRECIPITATION TO 
BEGIN AT KRDD AND KRBL BETWEEN 03Z AND 09Z WITH WIDESPREAD IFR TO 
LIFR CIGS/VISBYS POSSIBLE. SNOW LEVELS WILL BEGIN AT 3500 TO 4500 FT 
AND GRADUALLY RISE TUESDAY. PRECIPITATION SHOULD FOR THE MOST PART 
REMAIN NORTH OF I-80 CORRIDOR THROUGH TUESDAY. PATCHY MVFR TO IFR BR 
POSSIBLE AT SACRAMENTO AND KSCK TAFS TONIGHT INTO TUESDAY MORNING. 

&&

.STO WATCHES/WARNINGS/ADVISORIES...
...WINTER STORM WARNING FROM 4 AM TUESDAY TO 4 PM PST WEDNESDAY FOR 
   WESTERN PLUMAS COUNTY/LASSEN PARK.
...WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 4 AM PST 
   WEDNESDAY FOR BURNEY BASIN / EASTERN SHASTA COUNTY-SHASTA LAKE 
   AREA / NORTHERN SHASTA COUNTY.

&&

$$