Heavy Snow in California, December 6 to 7, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
400 AM PST THU DEC 6 2007

.SHORT TERM...THURSDAY THROUGH FRIDAY NIGHT...
UPGRADED WINTER STORM WATCHES TO HEAVY SNOW WARNINGS AND PUT UP A
WINTER STORM WATCH FOR ZONE 1 (WE NOW HAVE STATEMENTS OUT FOR EVERY
ZONE IN THE CWA).

VIGOROUS SHORT WAVE TO BRING THE FIRST SIGNIFICANT WINTER STORM TO
THE REGION IS CURRENTLY LOCATED AT 42N AND 135W...OR ABOUT 550 MILES
WEST OF ARCATA CALIFORNIA. UNDERNEATH THE SHORT WAVE...A PRECIPITABLE
WATER PLUME OF 1.2 TO 1.8 INCHES EXTENDS FROM JUST OFF THE NORTHERN
CALIFORNIA COAST SOUTHWEST TO HAWAII...ALONG WITH A RIPPING 160 KT
JET CORE. THE SHORT WAVE WILL MOVE EAST SOUTHEAST TODAY AND POINT
THE DEEP MOISTURE PLUME AT THE NORTHERN/CENTRAL SIERRA AND WESTERN
NEVADA BY LATE AFTERNOON. THE PLUME WILL SLAM INTO THE SIERRA AND
KEEP GOING RIGHT INTO WESTERN NEVADA THIS AFTERNOON WITH WEAK
INSTABILITY AND DEEP MOISTURE TO PREVENT MUCH SHADOWING.

TONIGHT AND FRIDAY MORNING...THINGS REALLY WIND UP WITH THE STORM
SYSTEM AS IT IS VERY WELL PROGGED TO MOVE TO BETWEEN LAKE TAHOE AND
SAN FRANCISCO BY EARLY FRIDAY MORNING. PATTERN RECOGNITION INDICATES
THAT THIS AN EXCELLENT POSITION FOR HEAVY SNOW FOR PORTIONS OF THE
WESTERN GREAT BASIN. OF CRITICAL IMPORTANCE FOR THE RENO AREA IS THE
POSITION OF A DRY SLOT/JET CORE WORKING AROUND THE SOUTHEASTERN
PERIPHERY OF THE UPPER LOW. THE DRY SLOT IS PROGGED TO MOVE TO NEAR
OR A BIT SOUTH OF RENO DEPENDING ON THE EXACT TRACK OF THE LOW. IF
THE SLOT SETS UP SOUTH OF RENO...THERE WILL BE A HEAVY BURST OF SNOW
APPROXIMATELY BETWEEN 9 PM THURSDAY AND 4 AM FRIDAY WITH THE
STRONGEST UPPER MOTION IN THE LEFT FRONT QUAD OF THE POWERFUL JET
STREAK. WITH WRAP AROUND SNOW VERY LIKELY ANYWAY...THE POSSIBLE
BURST OF HEAVY SNOWFALL WOULD REALLY RAMP UP SNOWFALL TOTALS BETWEEN
THURSDAY EVENING AND FRIDAY MORNING. MODELS/SREF ENSEMBLE QPF SEEMS
TO INDICATE THAT A HEAVIER BAND WILL DEVELOP BEFORE 12Z FRIDAY
SOMEWHERE ALONG THE INTERSTATE 80 CORRIDOR. WITH THIS IN MIND...I
UPGRADED TO A HEAVY SNOW WARNING FOR ZONES 3/4 (RENO/LOVELOCK/FALLON)
THURSDAY NIGHT AND FRIDAY. FRIDAY MORNINGS COMMUTE COULD BE HAIRY
INDEED (ESPECIALLY WHEREVER THE EXPECTED HEAVY BURST OF SNOW
DEVELOPS) FOR RENO. FURTHER SOUTH...I ADDED A WINTER STORM WATCH TO
ZONE 1 AS THE POTENTIAL EXISTS FOR THE HEAVIER SNOWBAND TO THE NORTH
TO MOVE SOUTH INTO MINERAL AND SOUTHERN LYON COUNTIES FRIDAY MORNING.
SNYDER

.LONG TERM...SATURDAY THROUGH WEDNESDAY
FOR SATURDAY...MODELS ARE SHOWING AN INSIDE SLIDER TO BRING COLDER
AIR INTO THE REGION. THE GFS AND EURO CONTINUE TO BE FAIRLY FAR WEST
WITH THE 500 MB COLD POOL MOVING DIRECTLY OVERHEAD. A FEW SNOW
SHOWERS REMAIN POSSIBLE...MAINLY IN THE UPSLOPE AREAS SOUTH OF RENO
IN NORTHEAST FLOW. HOWEVER...WITH WEAK WIND SHEAR...THERE IS THE
POTENTIAL FOR SOME LAKE EFFECT. DO NOT THINK IT WOULD BE A BIG EVENT
AS IT WOULD OCCUR DURING THE DIURNAL MINIMUM FOR LES BUT A COUPLE
INCHES ARE POSSIBLE ON THE SOUTH SHORES OF TAHOE...PYRAMID AND
WALKER LAKES.

FEW CHANGES MADE TO THE EXTENDED AS UPPER LOW MOVES INTO DESERT SW
WITH POSITIVE TILT RIDGE SLOWLY BUILDING INTO THE REGION. FLOW WILL
GENERALLY REMAIN NORTH AND DRY. DO NOT EXPECT MUCH CLOUD COVER
EXCEPT FOR SOME MID AND HIGH CLOUDS ACROSS THE NORTH. WITH THIS FLOW
PATTERN...EXPECT TEMPERATURES TO REMAIN BELOW NORMAL. A SLOW WARMING
TREND IS DEPICTED CLOSER TO NORMAL. IF THERE IS ENOUGH CLOUD COVER
FROM TONIGHTS STORM...TEMPS COULD BE COLDER BECAUSE INVERSIONS WILL
TAKE HOLD OVER WRN NV. SIERRA TEMPS WILL SEE THE WARM-UP...BUT IT
WILL BE GRADUAL. A FEW SHORT WAVES WILL PASS BY TO THE NORTH BUT DO
NOT EXPECT ANY PRECIPITATION AT THIS TIME. WALLMANN &&

.AVIATION...
VERY HIGH CONFIDENCE IN THE APPROACHING WINTER STORM. PRECIP WILL BE
ALL SNOW FOR KTVL-KTRK AND VIS WILL TAKE SOME TIME TO DROP. MVFR
CIGS WITH LCL IFR THROUGH 02Z THEN IFR THROUGH 12Z FOR THOSE
TERMINALS. PROB OF CIGS BLO 1SM IS 80 PCT WITH SEVERAL INCHES OF
SNOW TO FALL ON RUNWAYS.

FOR KRNO...PRECIP WILL BEGIN AS RAIN AS EARLY AS 20Z AND BE FAIRLY
LIGHT WITH MAINLY MVFR CIGS. EXPECT CHANGEOVER TO SNOW TO OCCUR
BETWEEN 03 AND 06Z WITH 80 PCT CONFIDENCE THE CHANGEOVER WILL OCCUR
DURING THIS TIME. AFTERWARD...IFR CIGS/VIS THROUGH 15Z WITH
OCCASIONAL BREAKS. EXPECT 2-3 INCHES OF SNOW ON RUNWAYS WITH BEST
CHANCE OF ACCUMULATION BETWEEN 09 AND 15Z.

FOR KLOL...LOWER ELEVATIONS HERE WILL KEEP PRECIP ALMOST ALL RAIN.
CIGS WILL BE REDUCED TO NEAR 2KFT IN THE RAIN WITH PEAK PERIOD
BETWEEN 00 AND 09Z.

EXPECT GRADUALLY IMPROVING CONDITIONS FRIDAY AFTERNOON ALL
TERMINALS. WALLMANN
&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER STORM WARNING FROM 10 AM THIS MORNING TO 10 AM PST
     FRIDAY FOR NVZ002.

     HEAVY SNOW WARNING FROM 1 PM THIS AFTERNOON TO 7 AM PST FRIDAY
     FOR NVZ005.

     WINTER STORM WATCH FROM LATE TONIGHT THROUGH FRIDAY AFTERNOON
     FOR NVZ001.

     HEAVY SNOW WARNING FROM 7 PM THIS EVENING TO 12 PM PST FRIDAY
     FOR NVZ003-004.

CA...WINTER STORM WARNING FROM 10 AM THIS MORNING TO 10 AM PST FRIDAY
     FOR CAZ071-072.

     HEAVY SNOW WARNING FROM 1 PM THIS AFTERNOON TO 7 AM PST FRIDAY
     FOR CAZ070.

     WINTER STORM WARNING FROM 4 PM THIS AFTERNOON TO 4 PM PST FRIDAY
     FOR CAZ073.
&&

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