FXUS65 KREV 061054
AFDREV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
254 AM PST SUN DEC 6 2009

.SHORT TERM...
COLD CORE OF SECONDARY UPPER LOW IS EVIDENT ON SATELLITE IMAGERY
THIS MORNING OVER OREGON AS OF 10Z. THIS LOW WILL CONTINUE TO DROP
SOUTH TODAY...ALONG THE TROUGH OVER THE WESTERN CONUS...AND WILL
DIG WESTWARD BY TONIGHT INTO CA AND NV. THE JET MAX DIGGING AROUND
THE BASE OF THE TROUGH HAS AN OVER WATER TRAJECTORY AND WILL
ENTRAIN A WAVE OF PACIFIC MOISTURE INTO IT AS IT APPROACHES THE
CWA. THE COLD AIR MASS COMBINED WITH MOISTURE AND EXCELLENT
DYNAMICS WILL BE PERFECT FOR GENERATING SNOW. SNOW RATIOS ARE
EXPECTED TO BE IN THE 20-30 TO 1 RANGE IN THIS STORM WITH H7
TEMPERATURES IN THE -14 TO -18 DEGREE C RANGE EVEN DOWN TO THE
LOWEST VALLEY FLOORS. THE MOIST WAVE WILL ROTATE AROUND THE BASE
OF THE WESTERN TROUGH EJECTING EASTWARD MONDAY NIGHT... TAKING THE
SNOW WITH IT.

HAVE UPGRADED ALL AREAS IN THE WATCH TO A WINTER STORM WARNING
WHICH WILL BE ISSUED SHORTLY. IN ADDITION WILL BE ISSUING A SNOW 
ADVISORY FOR SURPRISE VALLEY AND NORTHERN WASHOE COUNTY. ALL OF
THE ABOVE WILL BE IN EFFECT FROM SUNDAY NIGHT THROUGH MONDAY
NIGHT. SNOW TOTALS IN THE VALLEYS OF THE WARNED AREAS WILL BE 5 TO
10 INCHES WITH 25-30 INCHES IN THE HIGHER ELEVATIONS OF THE SIERRA.
THE ADVISORY AREA WILL SEE 3 TO 5 INCHES. SEE RNOWSWREV FOR
ADDITIONAL DETAILS OF THE ADVISORY AND WARNINGS.

UPPER LEVEL WINDS WILL BE STRONG AS THIS SYSTEM DROPS SOUTH WITH
RIDGES GUSTING 55-75 MPH. LAKE LEVEL WINDS WILL BE GUSTING 30-40
MPH SO HAVE CONTINUED WITH THE LAKE WIND ADVISORY FOR TAHOE. WILL
BE ENDING THE ADVISORY 3 HOURS EARLIER...AT 7 PM PST...BECAUSE THE
WINTER STORM WARNING WILL BE STARTING AT THAT POINT. 

THE SYSTEM WILL LEAVE AN EXTREMELY COLD AIR MASS IN ITS WAKE AND
THE QUESTION IS JUST HOW COLD IT BE TUESDAY AND WEDNESDAY
MORNINGS. BROUGHT LOW TEMPERATURES UP A DEGREE OR TWO TUESDAY
MORNING AS IT APPEARS THERE WILL BE SOME REMNANT CLOUDS OVER THE
AREA. WITH THE UPSTREAM SYSTEM SLOWER TO COME IN...WEDNESDAY
MORNING WILL BE CLEAR...AND WITH LIGHT WINDS AND SNOW COVER...
TEMPERATURES SHOULD PLUNGE. DROPPED TEMPS ABOUT 5 DEGREES ACROSS
THE AREA WEDNESDAY MORNING. EXPECT WIDESPREAD SINGLE DIGIT TEMPS
WITH MANY PLACES EVEN DROPPING BELOW ZERO BOTH MORNINGS. DF

.LONG TERM...WEDNESDAY THROUGH SATURDAY...
MODELS CONTINUE TO BACK OFF ON LATE WEEK SYSTEM AND NOW DELAY 
ARRIVAL UNTIL POSSIBLY THURSDAY MORNING. IN ADDITION...SYSTEM 
LOOKING LESS AND LESS ORGANIZED WITH EACH RUN AND QPF ALONG SIERRA 
CREST NOW DOWN TO ONLY 1-1.5 INCHES. HAVE GONE DRY NOW FOR WED...AND 
WITH REINFORCING SHOT OF COLD AIR OVERNIGHT...HAVE LOWERED TEMPS 
ABOUT 5 DEGREES...WITH HIGHS STRUGGLING TO REACH 30 ONCE AGAIN 
THROUGHOUT WRN NV. EXPECT CLOUD COVER TO MOVE IN WED NIGHT...BUT NOT 
SURE ABOUT PRECIP TIMING. GEFS A BIT FASTER THAN OPERATIONAL GFS/EC 
SO HAVE LEFT POPS IN...BUT DRASTICALLY REDUCED THEM. 

SYSTEM APPEARS TO HIT THU/THU NIGHT AND SAME REASONING WITH SNOW 
LEVELS APPLY AS BEFORE. SFC GRADIENT REMAINS EAST SO EXPECT COLD AIR 
DAMMING IN THE LEE OF SIERRA AND JUST ABOUT AN ALL SNOW EVENT. SNOW 
LEVELS MAY BRIEFLY RISE FRI MORNING TO NEAR 5000 FEET...BUT THIS IS 
NOW BECOMING LESS LIKELY AS THE TREND IS FOR THE SYSTEM TO TRACK 
FURTHER SOUTH. KEPT THE HIGH POPS IN DURING THIS TIME...BUT DID NOT 
ADJUST UPWARD. GIVEN THE TREND OF THE MODELS BACKING 
OFF...CONFIDENCE IS NOW QUITE LOW WITH THIS SYSTEM DOING ANYTHING 
SIGNIFICANT. NEW 06Z GFS IS ALARMING IN THAT IS ALMOST COMPLETELY 
LOSES THE SYSTEM BY THE TIME IT ARRIVES. THIS WILL BE TREATED AS AN 
OUTLIER RIGHT NOW...BUT GIVEN THE POTENTIAL SYSTEM SAT IT CANNOT BE 
COMPLETELY DISCOUNTED EITHER.

FRI THERE IS SOME SHORT WAVE RIDGING...BUT NOW MODELS ARE IN GOOD 
AGREEMENT WITH A WETTER SYSTEM FOR NEXT WEEKEND THAT COMES IN 
PIECES. HAVE KEPT CHC POPS IN THE SIERRA WITH LOW CHC TO SLIGHT CHC 
WRN NV OVER THE WEEKEND. REALLY HAVE NO CONFIDENCE TO GO HIGHER 
DESPITE EXCELLENT MODEL AGREEMENT. MODELS WERE QUITE WET WITH THU 
SYSTEM 3-4 DAYS AGO AND HAVE SIGNIFICANTLY BACKED OFF. PREFER TO 
WAIT ON THIS ONE RIGHT NOW. IF IT DOES OCCUR...COULD BE IMPRESSIVE 
AND WILL BE WARMER...BUT SNOW LEVELS DO NOT LOOK TO RISE ABOVE 6000 
FEET WITH THAT ONE EITHER. WALLMANN

&&

.AVIATION...VFR CONDS WITH BRISK SW-W WINDS GUSTING TO 30 KT AT
KRNO/KTVL/KTRK FM 19Z THRU 03Z. WINTER STORM SET TO IMPACT THE
AREA BEGINNING AROUND 03Z FOR KTVL/KTRK AND 09-15Z FOR KRNO-
KLOL...DETAILS BELOW.

FOR KTVL/KTRK...EXPECT MVFR CIGS/VIS BY 03Z MON WITH IFR AFT 06Z. 
LIFR CONDS...ABOUT 70 PCT CHC...AFT 12Z CONTINUING THRU AT LEAST 21Z 
MON IN MDT-HVY SNOW. SIGNIFICANT RUNWAY ACCUMULATIONS WITH A FOOT OR 
MORE POSSIBLE.

KRNO...EXPECT LGT -SN TO MOVE IN AFT 09Z WITH OCNL MVFR CIGS/VIS 
THRU 15Z. THEN PDS OF IFR...90 PCT CHC...AND POSSIBLY LIFR THRU 
21-00Z IN BANDS OF MDT SNOW. RUNWAY ACCUMULATION LIKELY WITH VERY 
COLD TEMPS DURING SNOWFALL...IN THE 20S. AROUND 4 INCHES OR 
SO...50-60 PCT PROBABILITY WITH MORE POSSIBLE. 

KLOL...MAINLY VFR HERE...BUT PDS OF IFR CIGS/VIS FM 15-21Z IN 
LGT-MDT SNOW. LGT RUNWAY ACCUMS POSSIBLE. WALLMANN

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 PM PST MONDAY 
     FOR NVZ002.

     WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 4 PM PST 
     MONDAY FOR NVZ005.

     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 7 PM PST MONDAY 
     FOR NVZ003.

     LAKE WIND ADVISORY FROM 10 AM THIS MORNING TO 7 PM PST THIS 
     EVENING FOR NVZ002.

CA...WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 PM PST MONDAY 
     FOR CAZ071-072.

     WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 4 PM PST 
     MONDAY FOR CAZ070.

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

     LAKE WIND ADVISORY FROM 10 AM THIS MORNING TO 7 PM PST THIS 
     EVENING FOR CAZ072.

&&

$$

HTTP://WEATHER.GOV/RENO