FXUS65 KREV 051426 AAA
AFDREV

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RENO NV
626 AM PST SAT DEC 5 2009

.UPDATE...
FRONT HAS PUSHED SOUTH OF I-80 ALREADY AND CONTINUES TO PUSH SOUTH
WITH STG COLD AIR ADVECTION BEHIND IT. TEMPS NORTH OF THIS AREA
HAVE LIKELY ALREADY SEEN THEIR HIGH FOR TODAY EARLIER THIS AM.
QUICK UPDATE TO LOWER HIGHS WHERE FRONT HAS PUSHED THROUGH. FCST
OF SNOW SHOWERS LOOKS ON TRACK AS BAND BEHIND FRONT REMAINS
DISORGANIZED WITH LITTLE SHOWING UP ON RADAR. DO EXPECT SCT SNOW
SHOWERS SOTH OF I-80 AND WEST OF HWY 95 THIS AFTERNOON WITH ONLY
LOCAL MINOR ACCUMULATION. WALLMANN

&&

.PREVIOUS DISCUSSION... /ISSUED 329 AM PST SAT DEC 5 2009/ 

SHORT TERM...
COLD FRONTAL BOUNDARY IS EVIDENT IN THE SATELLITE IMAGERY AND AS
OF 11Z IS RIGHT ALONG THE NV/ORE/ID BORDER. THE FRONT AND THE
ASSOCIATED UPPER LEVEL TROUGH WILL PUSH INTO THE AREA TODAY
BRINGING GUSTY WINDS AHEAD OF IT AND COOLER TEMPERATURES BEHIND
IT. THERE IS INTENSE FRONTOGENESIS AND LIFT WITH THIS SYSTEM AS IT
MOVES INTO OUR CWA...THOUGH MOISTURE IS LACKING. STILL...THE
DYNAMICS WILL BE ENOUGH TO GENERATE ISOLATED TO SCATTERED SNOW
SHOWERS ACROSS THE CWA THROUGHOUT THE DAY. COLD AIR AND MOISTURE
BANKING UP ALONG THE SOUTHERN SIERRA WILL KEEP SCATTERED SNOW
SHOWERS ACROSS MONO COUNTY THROUGH THE EVENING.

GUSTY FRONTAL WINDS WILL CREATE CHOPPY WATERS ON BOTH LAKE TAHOE
AND PYRAMID LAKE THROUGHOUT THE DAY. THEREFORE WILL CONTINUE THE
LAKE WIND ADVISORY FROM 8 AM THIS MORNING THROUGH 6 PM THIS
EVENING FOR BOTH LAKES. THERE IS A GOOD CHANCE TAHOE WILL BE
SEEING ADVISORY CRITERIA ONCE AGAIN SUNDAY INTO MONDAY AS WINDS
INCREASE AHEAD OF THE NEXT SYSTEM TO MOVE INTO THE AREA.

THE ABOVE MENTIONED SYSTEM WILL BE A REINFORCING SHOT OF COLD AIR
THAT WILL HELP TO PLUNGE TEMPERATURES 15-20 DEGREES BELOW NORMAL
MONDAY INTO TUESDAY...POSSIBLE LASTING INTO THE THE LONG TERM
PERIOD. THIS COLD LOW WILL MERGE WITH A WAVE OF MOISTURE COMING IN
FROM THE PACIFIC...THE PERFECT RECIPE FOR SNOW. PW VALUES ARE HIGH
FOR A SYSTEM THIS COLD THE AND GEFS IS INDICATING A 70-100 PERCENT
CHANCE OF A TENTH OF AN INCH QPF IN A 12 HOUR PERIOD THROUGH MUCH
OF THE CWA MONDAY. SNOW RATIOS WILL BE IMPRESSIVE WITH SUCH A COLD
AIR MASS IN PLACE...20-30:1 RATIOS WILL BE COMMON. THE BEST
SNOWFALL WILL BE SUNDAY NIGHT THROUGH MONDAY NIGHT WITH ABOUT A
FOOT AT LAKE LEVEL AND UP TO 2 FEET ABOVE 7000 FT IN THE SIERRAS.
VALLEYS JUST EAST OF THE SIERRAS WILL SEE UP TO 6 INCHES BY THE
END OF THE EVENT. THEREFORE WILL SOON BE ISSUING A WINTER STORM
WATCH FOR THE TIMES LISTED BELOW. THIS SYSTEM WILL HAVE A
SIGNIFICANT IMPACT ON TRAVEL MONDAY MORNING. KEEP UP WITH THE
LATEST FORECASTS THROUGH THE WEEKEND FOR TRAVEL IMPACTS ON MONDAY.

LOW TEMPERATURES TUESDAY MORNING WILL LIKELY DIP INTO THE SINGLE
DIGITS TO BELOW ZERO...THOUGH EXACTLY HOW COLD WILL DEPEND ON
HOW MUCH WE CLEAR BEHIND THE STORM. NO MATTER WHAT...TUESDAY WILL
BE QUITE COLD. DF

LONG TERM...TUESDAY THROUGH FRIDAY...
MODELS CONTINUE IN BETTER AGREEMENT...ALTHOUGH 06Z GFS IS QUITE 
DIFFERENT...BUT IS SUCH AN OUTLIER IT WILL BE DISCOUNTED FOR NOW. 
OVERALL JUST MADE MINOR TWEAKS TO THE EXTENDED AS OVERALL IT LOOKED 
GOOD. MAIN CHANGES WERE TO INCREASE SOME POPS FOR WED NIGHT/THU AND 
ALSO LOWER SNOW LEVEL WED NIGHT.

SOME SHORT WAVE RIDGING LOOKS GOOD FOR TUE/TUE NIGHT WITH VERY COLD 
AIR IN PLACE AND TEMPS 20 DEGS BELOW NORMAL BEFORE NEXT SYSTEM SET 
TO ARRIVE WED INTO THU IN A COUPLE PIECES. GFS/EC CONTINUE TO DIFFER 
WITH TIMING AND EC IS ABOUT 12 HRS FASTER. SLOWER GFS SUPPORTED BY 
GEFS AND GEM SO LEANING TOWARDS 00Z GFS TIMING AS PRECIP IS WARM 
FRONTAL AND THERE WILL BE QUITE A BIT OF LLVL DRY AIR TO OVERCOME 
INITIALLY.

H7 TEMPS TO RISE AS HIGH AS -3 TO -4 C OVERNIGHT WED NIGHT...BUT THE 
LLVL COLD AIRMASS WILL STILL BE IN IN PLACE SO EXPECT SNOW FOR ALL 
AREAS WED UNTIL ABOUT MIDNIGHT WED NIGHT. MODEL SOUNDINGS SHOW 
ISOTHERMAL PROFILE FROM SFC TO 700 MB WHICH MAKES SENSE GIVEN THE 
PATTERN AND COLD AIR DAMMING ON LEE SIDE OF SIERRA. SNOW LEVELS TO 
RISE POSSIBLY TO 5000-5500 FEET THU BEFORE COLD FRONT WITH SYSTEM 
MOVES IN. SYSTEM WILL HAVE PLENTY OF MOISTURE BUT IS NOT OVERLY 
DYNAMIC SO TOTAL QPF AMOUNTS OF 2-3 INCHES NEAR THE CREST LOOK GOOD 
OFF THE GFS/EC/GEM WITH LIGHTER AMOUNTS IN THE LEE. 

BEHIND THE SYSTEM FRIDAY THERE ARE SOME WEAK SHORT WAVES TO MOVE THROUGH
BUT THE BRUNT OF THE WAVES WILL REMAIN SOUTH. KEPT IN CHC TO
SLIGHT CHC POPS FOR THESE WAVES...BUT NONE LOOK SIGNIFICANT THIS
FAR NORTH. TEMPS WILL MODERATE BACK CLOSER TO NORMAL BY FRI.
WALLMANN

AVIATION...OLD FRONT TO DROP SWD TODAY WITH PASSAGE THRU KLOL
16Z...KRNO/KTRK 18Z AND KTVL 20Z WITH WINDS BECOMING NORTH
BEHIND IT WITH GUSTS TO 25 KTS. EXCEPTION WILL BE KTVL WHICH WILL
TAKE LONGER TO SWITCH TO NORTH DUE TO CHANNELING ALONG UPR TRUCKEE
RIVER DRAINAGE. EXPECT MAINLY VFR CONDS. BRIEF PD OF IFR CIGS/VIS
TO 45 MINS POSSIBLE FOR KRNO/KTRK/KTVL ABOUT 2 HRS BEHIND FRONT.
POTENTIAL BAND OF LGT-MDT SNOW LOOKS TO DEVELOP JUST SOUTH OF
THESE TERMINALS...BUT CHC OF IT AFFECTING TERMINALS IS NEAR 30-40
PCT. LITTLE ACCUMULATION EXPECTED.

WINDS TO INCREASE ON SUN AGAIN FROM WEST AHEAD OF ANOTHER STG COLD 
FRONT. THIS ONE LOOKS TO HAVE MORE MOISTURE BY MON MORNING WITH 
POTENTIAL OF A SIGNIFICANT STORM TO AFFECT TERMINALS...MAINLY 
KRNO/KTVL/KTRK. WALLMANN

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY EVENING 
     FOR NVZ002.

     WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY EVENING 
     FOR NVZ003.

     LAKE WIND ADVISORY UNTIL 6 PM PST THIS EVENING FOR NVZ002-004.

CA...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY EVENING 
     FOR CAZ071-072.

     WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY EVENING 
     FOR CAZ073.

     LAKE WIND ADVISORY UNTIL 6 PM PST THIS EVENING FOR CAZ072.

&&

$$

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