Heavy Snow in California, December 14 to 15, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
223 PM PST SUN DEC 14 2008

.SHORT TERM...INITIAL SLUG OF MOISTURE IS MOVING INTO THE WEST
SLOPES OF THE SIERRA ATTM WITH LIGHT RAIN NOTED IN RADAR IMAGERY
WEST OF THE SIERRA WHILE LIGHT SNOWS HAVE DEVELOPED IN THE HIGHER
ELEVATIONS. WATER VAPOR IMAGERY SHOWS DEVELOPING LOW ALOFT JUST OF
THE WA COAST THIS AFTN. THIS LOW WILL DROP SOUTH WITH MODELS IN
GENERAL AGREEMENT THAT IT WILL EITHER HUG THE COAST OR MOVE JUST
INLAND BY LATE MON THEN OPEN INTO A WAVE BY LATE TUES.

A SERIES OF SHORT WAVES ROTATING THROUGH THE OVERALL LONG WAVE TROF
AHEAD OF THIS LOW WILL PRODUCE PERIODS OF SNOW OVER MUCH OF THE
RGN FROM THIS EVENING THROUGH MON NIGHT. WHILE PWATS WILL CONTINUE
FAIRLY LOW OVER MUCH OF OUR AREA...THE AIRMASS IS VERY COLD AND
SNOW TO LIQUID WATER RATIOS SHOULD INCREASE TO 15 TO 1 OR MORE.
QPF FORECASTS HAVE INCREASED IN THE LAST 24 HOURS AND IF THE LOW
DROPS A BIT FARTHER WEST AND IS ABLE TO TAP MORE MSTR FROM THE E
PAC THESE COULD INCREASE EVEN MORE. WITH THE INCREASING QPF AND
FAIRLY HIGH SNOW TO LIQUID RATIOS HAVE OPTED TO BUMP UP SNOW
AMOUNTS AND EXTEND THE WINTER STORM WARNINGS UNTIL 16/06 UTC. WILL
ALSO ISSUE WINTER WEATHER ADVISORIES FOR NVZ001 AND NVZ004.
AMOUNTS IN THESE LOCATIONS WILL BE MUCH LESS BUT SHOULD REACH LOW
END ADVISORY CRITERIA OF AROUND 3 TO 4 INCHES IN THE VALLEYS.

SNOW SHOULD COME IN A SERIES OF PULSES ASCD WITH THE SHORT WAVES.
LOCALLY RUN WRF SHOWS PERIODS OF QPF OF AS MUCH AS 0.30 INCHES IN
AN HOUR IN THE HIGHER ELEVATIONS BY MON MRNG. SO WHILE THIS MAY
NOT BE A CONTINUOUS EVENT...FELT THAT THE BREAKS IN THE SNOWFALL
WOULD NOT BE SUFFICIENT TO LESSEN IMPACTS BETWEEN THE PULSES.
WARNINGS COULD POSSIBLY NEED EXTENDING BEYOND 16/06 UTC AS LONG
WAVE TROF DOES NOT MOVE THROUGH MUCH OF THE RGN UNTIL AROUND 16/12
UTC. LATER SHIFTS CAN LOOK AT THIS.

OMEGA IS VERY IMPRESSIVE WITH THIS SYSTEM AND MODEL SOUNDINGS SHOW
A FAIRLY SATURATED AIRMASS BY THIS EVENING OVER MUCH OF THE RGN.
INSTABILITY SHOULD NOT BE AN ISSUE EITHER SO SPILL OVER SHOULD
OCCUR FAIRLY QUICKLY. THUS WHILE SIERRA WILL RECEIVE BY FAR THE
HEAVIEST SNOWS...PERIODS OF HEAVY SNOW WILL LIKELY IMPACT THE
RENO/SPARKS AREA AS WELL. THE HEAVIEST SNOWS IN BOTH THE SIERRA
AND TO THE EAST FALL LATE THIS EVENING AND AGAIN FROM AROUND 5 AM
TO 10-11 AM MONDAY MRNG. THIS COULD MAKE THE MORNING COMMUTE
ESPECIALLY HAZARDOUS. MLF

BY TUESDAY...THE LOW CENTER IS EXPECTED TO WEAKEN AND MOVE INLAND
ACROSS NRN CA AND THEN MAKE ITS WAY SOUTH ALONG THE SACRAMENTO
VALLEY. WHILE THE STEADY STRATIFORM PRECIP ASSOCIATED WITH THIS
SYSTEM WILL BE WELL SOUTH OF THE REGION...INCREASING INSTBY IS
LIKELY TO TRIGGER CONVECTIVE SNOW SHOWER BANDS OVER THE SIERRA.
AREAS UNDER THE HEAVIER BANDS...WHICH MAY INCLUDE ANYWHERE FROM
PLUMAS COUNTY SOUTH ACROSS THE TAHOE BASIN TO MONO COUNTY...COULD
RECEIVE SEVERAL ADDITIONAL INCHES OF SNOW...WITH THE EXACT LOCATION
OF THE HEAVIER SNOWFALL BEING THE MAIN UNCERTAINTY. SOME OF THESE
SHOWERS SPILLING INTO THE HIGHWAY 395 CORRIDOR WILL PRODUCE LOCAL
ACCUMULATIONS OF AN INCH OR TWO...ALTHOUGH THE POTENTIAL EXISTS FOR
A NARROW BAND OF LAKE ENHANCEMENT SETTING UP BETWEEN RENO AND CARSON
CITY. THE SHOWER ACTIVITY WILL TAPER OFF FROM NORTH TO SOUTH TUES
NIGHT AS THE LOW OPENS UP AND CONTINUES MOVING SOUTH...WITH
LINGERING SNOW SHOWERS LIMITED TO MONO COUNTY AFTER MIDNIGHT. TEMPS
WILL REMAIN QUITE COLD WITH MOST VALLEYS REMAINING BELOW 30 DEGREES
ON TUESDAY...THEN PLUNGING INTO THE SINGLE DIGITS TUES NIGHT. MJD

.LONG TERM...WEDNESDAY THROUGH SUNDAY...
THE EARLY WEEK STORM SYSTEM EXITS THE REGION TUESDAY NIGHT INTO
EARLY WEDNESDAY LEAVING A VERY COLD AIRMASS IN ITS WAKE. WITH LOTS
OF FRESH SNOW COVER...ANY NIGHT THAT IS CLOUD-FREE WITH RELATIVELY
LITTLE WIND WILL RESULT IN MAXIMUM RADIATIONAL COOLING THAT WILL
DROP VALLEY TEMPERATURES INTO THE SINGLE DIGITS AND HIGH VALLEY
READINGS...SUCH AS IN TRUCKEE AND BODIE...WELL BELOW ZERO.
TEMPERATURES FOR MIDWEEK WILL BE WELL BELOW NORMAL WITH SOME
GRADUAL MODERATION BY THE END OF THE WEEK.

A BROAD TROUGH IS ESTABLISHED ACROSS THE CONUS THROUGH THIS PERIOD
WITH NORTHERN CA AND NEVADA IN A GENERAL WEST TO NORTHWEST FLOW
ALOFT. IMPULSES ROTATING THROUGH THIS FLOW WILL WARRANT A CHANCE OF
SHOWERS ACROSS THE SIERRA AND IN THE NEVADA VALLEYS NORTH OF
INTERSTATE 80 THROUGH THE PERIOD. A SHORTWAVE MOVING ACROSS THE AREA
FRIDAY WILL BRING A SHOT OF REINFORCING COLD AIR. THE EC SWINGS THIS
ACROSS FAR NORTHERN CA/NV WHILE THE GFS KEEPS THE ENERGY FURTHER
NORTH AND EAST. BY THE WEEKEND...WEST TO NORTHWEST FLOW ALOFT ALLOWS
FOR ONLY A MODEST WARM-UP...MAINLY AT HIGHER ELEVATIONS...AS WELL AS
PERIODS OF SNOW IN THE SIERRA WITH ANY IMPULSES THAT MOVE THROUGH
THE MEAN FLOW. IN ADDITION...BY THE END OF THE WEEKEND BOTH THE GFS
AND EC DIG ANOTHER CLOSED LOW OFF THE PACNW COAST. IF THIS SOLUTION
WOULD PAN OUT IT COULD SET UP ANOTHER ROUND OF SIGNIFICANT
PRECIPITATION FOR THE SIERRA AND WESTERN VALLEYS EARLY NEXT WEEK. JAH
&&

.AVIATION...
LIFR CONDITIONS IN THE SIERRA THROUGH 18Z MONDAY WITH PERIODS OF
MODERATE TO HEAVY SNOW AND MOUNTAIN OBSCUREMENT. EXPECT A BURST OF
HEAVY SNOW AT KTRK AND KTVL FROM 04Z-08Z... AND AGAIN FROM 12Z TO
18Z.

KRNO - MVFR CONDITIONS IN LIGHT SNOW BY 02Z WITH CONDITIONS LOWERING
BY 05Z TO IFR CONDITIONS WITH CIGS BLO 010 AND VSBY AOB 1SM IN SNOW.
EXPECT PERIODS OF MODERATE TO BRIEF HEAVY SNOW AT KRNO FROM
05Z-09Z...AND AGAIN LATER IN THE MORNING AROUND 15Z.

FROM 00Z MONDAY THROUGH 06Z TUESDAY EXPECT SNOWFALL ACCUMULATIONS OF
A FOOT TO 18 INCHES AT SIERRA TAF SITES AND 4 TO 8 INCHES AT
KRNO...WITH 3-5 INCHES AT KLOL. BECAUSE OF THE VERY COLD AIRMASS AND
DYNAMIC NATURE OF THIS STORM SYSTEM WE EXPECT PERIODS OF HEAVY SNOW
THAT WILL ACCUMULATE QUICKLY ON RUNWAYS. JAH
&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER STORM WARNING UNTIL 10 PM PST MONDAY FOR NVZ002-005.

     WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 10 PM PST
     MONDAY FOR NVZ001-004.

     WINTER STORM WARNING FROM 4 PM THIS AFTERNOON TO 10 PM PST
     MONDAY FOR NVZ003.

CA...WINTER STORM WARNING UNTIL 10 PM PST MONDAY FOR CAZ070>072.

     WINTER STORM WARNING FROM 7 PM THIS EVENING TO 10 PM PST MONDAY
     FOR CAZ073.

&&

HTTP://WEATHER.GOV/RENO