FXUS65 KREV 280115 AAA
AFDREV

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RENO NV
515 PM PST FRI NOV 27 2009

.UPDATE...
BACK EDGE OF DEVELOPING DEFORMATION BAND IS FROM TRUCKEE TO COLD
SPRINGS TO PYRAMID LAKE. THREAT OF SNOW FOR LASSEN/PLUMAS HAS
REALLY ENDED WITH ONLY SCT SNOW SHOWERS EXPECTED SNOW THIS
EVENING. HAVE CANCELED ADVISORY THERE...BUT LEFT THE REMAINDER
INTACT. SNOW LEVELS ARE CURRENTLY AROUND 4800 FEET IN THE RENO
AREA AND SLOWLY FALLING AS COLDER AIR FILTERS IN. RAIN/SNOW NOW
SPREADING SWD INTO CARSON CITY AND THE CARSON/MASON VALLEYS.
REMAINDER OF FORECAST ON TRACK...ALTHOUGH ACCUMULATIONS FOR TAHOE
MAY BE TOO HIGH. UPDATES OUT BY 530 PM. WALLMANN

&&

.PREVIOUS DISCUSSION... /ISSUED 327 PM PST FRI NOV 27 2009/ 

SHORT TERM...
WEATHER PATTERN IS STILL EVOLVING LATE THIS AFTERNOON. MID/UPPER
LOW IS STILL FORECAST BY ALL MODELS TO CLOSE OFF AND DROP SOUTH
THROUGH CENTRAL CA LATE TODAY INTO SRN CA BY EARLY SATURDAY. TRACK
OF THIS LOW AND DEFORMATION ZONE DEVELOPMENT TO THE NORTHEAST WILL
DETERMINE IF/HOW MUCH SNOW FALLS IN THE SIERRA AND POINTS EAST.
CURRENTLY LOW IS TAKING SHAPE VICINITY SACRAMENTO AND RADAR ECHOES
ARE DEVELOPING AROUND THE LOW.

FIRST BAND OF PCPN PRODUCED LIGHT AMOUNTS OF SNOW IN THE NRN
SIERRA NORTH INTO LASSEN COUNTY EARLIER TODAY AND IS NOW PRODUCING
LIGHT RAIN IN SOME AREAS EAST OF THE SIERRA AND LIGHT SNOW IN THE
TAHOE BASIN. THIS BAND OF PCPN WAS INITIALLY ASCD WITH THE COLD
FRONT BUT MAY NOW START TO MORPH IN TO THE DEFORMATION AXIS AS IT
DEVELOPS THROUGH THE LATE AFTERNOON AND EARLY HOURS. HAVE SEEN
SNOW LEVELS DROP RATHER QUICKLY IN ANY PCPN TODAY AND ANTICIPATE
THIS WILL BE THE CASE THROUGH EVENING AS PCPN EVAPORATES IN SUB
CLOUD LAYER AND PCPN INTENSITY INCREASES. MODEL QPF STILL HINTS AT
BEST TOTALS OCCURRING SOUTH OF HIGHWAY 50 TONIGHT AND GIVEN THAT
THIS WILL BE MAINLY AN OVERNIGHT EVENT THINK ACCUMULATIONS OF 3 TO
6 INCHES WILL BE POSSIBLE IN MANY LOCATIONS. THUS HAVE OPTED TO
ISSUE WINTER WEATHER ADVISORIES FOR MONO COUNTY AND
MINERAL/SOUTHERN LYON COUNTIES FOR OVERNIGHT. WILL ALLOW LASSEN
COUNTY ADVISORY TO RUN INTO THE EVENING ALTHOUGH SNOW AMOUNTS HAVE
BEEN LIGHT THUS FAR. THINK THE SOUTHERN HALF OF THE ZONE WILL PICK
UP ADDITIONAL ACCUMULATIONS THIS EVENING. TAHOE AREA SHOULD SEE
LIGHT TO MODERATE SNOW CONTINUE THROUGH EVENING HOURS. FOR
RENO/CARSON CITY AREA THINK THE BEST ACCUMULATIONS WILL BE SOUTH
OF HIGHWAY 50 OVERNIGHT AND THIS ADVISORY MAY NEED TO BE EXTENDED
FOR SOUTHERN AREAS EARLY SATURDAY MORNING. IF DEFORMATION AXIS
DOES NOT DEVELOP AS FORECAST...OR LOW MOVES SOUTH TOO FAST...THEN
ACCUMULATIONS WILL BE MUCH LESS THAN FORECAST AND ADVISORIES WILL
HAVE TO BE DROPPED EARLY. SHOWERS LINGER INTO THE SRN SIERRA IN
UPSLOPE FLOW SATURDAY AFTN INTO THE EVENING. BEYOND THAT RIDGE
BEGINS TO BUILD INTO THE REGION WITH DRYING.

WINDS ARE ANOTHER ISSUE BY LATE SATURDAY. AS MID/UPPER LOW PULLS
SOUTH AND HIGH BEGINS TO BUILD NORTH OF THE RGN...THE LOW/MID LVL
GRADIENT WILL BEGIN TO TIGHTEN AND EASTERLY MID LVL WINDS AT THE
RIDGE TOPS WILL INCREASE WITH GUSTS REACHING UP TO 75 MPH. THESE
WINDS WILL LIKELY RESULT IN STRONGER WINDS ON LAKE TAHOE BY
SATURDAY NIGHT AND A LAKE WIND ADVISORY MAY BE NEEDED THERE.

THE INCREASED EAST TO NORTHEAST GRADIENT AT THE SFC WILL ALSO
RESULT IN COLDER AIR BEING PULLED SOUTH INTO THE RGN. THIS WILL
REINFORCE THE AIR MOVING IN BEHIND THE FRONT THIS EVENING AND
KEEP HIGHS BOTH SATURDAY AND SUNDAY IN THE 40S IN THE LOWER
VALLEYS AND 30S IN THE SIERRA VALLEYS. MLF

LONG TERM...TUESDAY THROUGH FRIDAY...
A FAIRLY PROGRESSIVE PATTERN WILL CONTINUE THROUGH NEXT WEEK WITH 
GENERALLY DRY CONDITIONS AND NEAR NORMAL TEMPERATURES FOR THE 
EASTERN SIERRA AND WESTERN NEVADA.

A FLAT RIDGE WILL BE IN PLACE FOR TUESDAY WITH A COOL NORTHERLY FLOW 
FOR WEDNESDAY. THE EC DROPS A SHORTWAVE ACROSS THE PACNW AND 
NORTHERN ROCKIES WHILE THE GFS IS FURTHER EAST WITH THE SHORTWAVE 
AND THUS WOULD KEEP OUR AREA A LITTLE WARMER AND LESS INFLUENCED BY 
THE NORTHERN SHORTWAVE. FOR LATER IN THE WEEK...THURSDAY AND 
FRIDAY...THE MEDIUM RANGE MODELS ARE WIDELY DIVERGENT AS ARE THE GFS 
ENSEMBLE MEMBERS. THE EC INDICATES A MUCH MORE AMPLIFIED PATTERN 
ACROSS NORTH AMERICA WITH A SPLITTING SYSTEM AFFECTING THE WEST 
COAST BY NEXT WEEKEND. THE DETERMINISTIC GFS BRINGS A SHORTWAVE 
ACROSS THE NORTHERN GREAT BASIN FOR THIS PERIOD WHICH WOULD RESULT 
IN BREEZY AND COOLER CONDITIONS FOR LATE IN THE WEEK. AGAIN THERE IS 
LITTLE ENSEMBLE SUPPORT FOR THE GFS SOLUTION AND MODEL TO MODEL RUNS 
HAVE SHOWN VIRTUALLY NO CONSISTENCY.

HAVE NOT MADE CHANGES TO THE CURRENT FORECAST BASED ON THE WIDELY 
DIVERGENT MODEL SOLUTIONS...WHICH KEEPS OUR REGION DRY AND CLOSE TO 
NORMAL WITH RESPECT TO TEMPERATURES. AS MENTIONED IN THE PREVIOUS 
FORECAST THE SUPER TYPHOON NIDA WHICH IS CURRENTLY IN THE FAR 
WESTERN PACIFIC MAY IMPACT WESTERN NORTH AMERICA SOMETIME NEXT 
WEEKEND SO WILL CONTINUE TO MONITOR ITS EVOLUTION. JAH

AVIATION...
COLD FRONT ROUGHLY JUST SOUTH OF I-80 THIS AFTERNOON WITH BAND OF 
MOISTURE ALONG AND BEHIND THE FRONT. FRONT WILL CONTINUE TO PUSH 
SOUTH TO BISHOP/TONOPAH BY 06Z. THERE WILL BE A PERIOD OF ABOUT 3-6 
HOURS OF SNOW JUST BEHIND THE FRONT AS SNOW LEVELS DROP RAPIDLY TO 
VALLEY FLOORS AND DEFORMATION AXIS ASSOCIATED WITH AN UPPER LOW 
SLIDING SOUTH ALONG THE SIERRA SETS UP. 

KTVL AND KTRK...WDSPRD MT OBSCUREMENT THIS EVENING THROUGH SATURDAY 
MORNING WITH LIFR/VLIFR CIGS AND VSBYS. EXPECT 2 TO 4 INCHES OF SNOW 
AT THESE SITES. SNOW WILL TAPER TO LIGHT SHOWERS BY 12Z. KTVL WILL 
SEE SOME LINGERING SHOWERS 12Z-18Z AS NORTHEAST WINDS ACROSS LAKE 
TAHOE PRODUCE SOME LIGHT LAKE EFFECT SNOW SHOWERS.

KRNO...SNOW LEVELS WILL DROP QUICKLY BEHIND THE FRONT AFTER 02Z TO 
THE VALLEY FLOOR. EXPECT A PERIOD OF BRIEF MODERATE OR POSSIBLY 
HEAVY SNOW BETWEEN 03Z-09Z. SNOW WILL ACCUMULATE ON RUNWAYS UP TO AN 
INCH OR POSSIBLY 2 AND ACCUMULATIONS COULD BE QUICK IF A HEAVIER 
BAND SETS UP OVER THE AREA. EVEN THOUGH SURFACE TEMPERATURES WILL BE 
CLOSE TO OR SLIGHTLY ABOVE FREEZING DURING THE PERIOD OF 
PRECIPITATION... SNOWFALL RATES SHOULD BE HIGH ENOUGH TO ALLOW 
ACCUMULATIONS AS MENTIONED. EXPECT SNOW TO TAPER OFF TO LIGHT 
SHOWERS BY 10Z OR SO.  

KLOL...PRECIPITATION WILL BEGIN AS RAIN THEN CHANGE TO LIGHT SNOW 
BEFORE MIDNIGHT WITH LITTLE ACCUMULATION. WINDS WILL VEER TO THE 
NORTHEAST BEHIND THE FRONT GUSTING TO 25KTS AFTER 03Z.  

CONDS WL IMPROVE BETWEEN 15Z-18Z TOMORROW AS DRY NORTHERLY FLOW SETS 
IN. EXPECT IFR CONDS AND MT OBSCUREMENT IN SNOW/CLOUDS AFTER 
MIDNIGHT AND DURING MUCH OF SATURDAY ALONG THE EASTERN SIERRA FROM 
BRIDGEPORT TO MAMMOTH LAKES AND SOUTH TO BISHOP. JAH

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 10 AM PST 
     SATURDAY FOR NVZ001.

     WINTER WEATHER ADVISORY UNTIL MIDNIGHT PST TONIGHT FOR NVZ002.

     WINTER WEATHER ADVISORY UNTIL 4 AM PST SATURDAY FOR NVZ003.

CA...WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 10 AM PST 
     SATURDAY FOR CAZ073.

     WINTER WEATHER ADVISORY UNTIL MIDNIGHT PST TONIGHT FOR CAZ072.

&&

$$

HTTP://WEATHER.GOV/RENO