FXUS65 KREV 071826
AFDREV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
ISSUED BY NATIONAL WEATHER SERVICE SACRAMENTO CA
1025 AM PST MON DEC 7 2009

.SHORT TERM...WATER VAPOR IMAGERY CONTINUES TO SHOW A COLD TROUGH OF 
LOW PRESSURE DIGGING OVER THE WEST...BRINGING A POWERFUL WINTER 
STORM TO CALIFORNIA AND NEVADA.  THE BACK EDGE OF PRECIPITATION BAND 
HAS JUST CLEARED THE SUSANVILLE AREA...WITH SKIES BEGINNING TO 
CLEAR.  HOWEVER...THE MAIN DEFORMATION BAND REMAINS OVER MUCH OF THE 
WARNING AREA...AS MODERATE SNOW CONTINUE TO FALL IN THE RENO...SOUTH 
LAKE TAHOE AND FALLOW STATION...WITH LIGHT SNOW IN THE LOVELOCK 
VICINITY.  EXPECT THIS SNOW TO CONTINUE THROUGH THE DAY...AND 
GRADUALLY TAPER OFF THIS EVENING AS THE DEFORMATION ZONE SWINGS 
SOUTH AND EAST.  HOWEVER...MAY ALSO SEE A RESURGENCE OF LAKE EFFECT 
SNOW BEHIND THE MAIN BAND FOR AREAS NEAR PYRAMID LAKE AND LAKE 
TAHOE.  THEREFORE...THE WINTER STORM WARNING REMAIN IN EFFECT.  MAIN 
CONCERN FOR TONIGHT THOUGH WILL BE WITH CLEARING SKIES AND 
TEMPERATURES ACROSS THE REGION.  WITH THE SNOW ON THE GROUND...VERY 
COLD AIR IN PLACE...RELATIVELY LIGHT WINDS...AND GOOD RADIATIONAL 
COOLING....TEMPERATURES WILL PLUMMET ACROSS THE REGION TONIGHT.  
EVEN AREAS IN THE VICINITY OF RENO MAY BE NEAR OR BELOW ZERO FOR THE 
FIRST TIME IN 11 YEARS.  CURRENT FORECAST LOOKS PRETTY GOOD...BUT 
WILL NEED TO TWEAK THE TEMPERATURES FOR TONIGHT.  PALMER

.PREVIOUS DISCUSSION (ISSUED AT 226 AM PST)...POWERFUL WINTER STORM 
IS BRINGING COPIOUS AMOUNTS OF SNOW ACROSS THE SIERRAS AND INTO 
WESTERN NEVADA. ABOUT 12-15 INCHES HAVE FALLEN SO FAR IN THE EASTERN 
SIERRAS WITH 3 TO 7 INCHES ACROSS WESTERN NEVADA. AS OF 145 AM PST 
THERE HAS BEEN ABOUT 5 INCHES AT THE RENO AIRPORT WITH SNOW STEADILY 
FALLING. WITH SUCH A COLD AIR MASS IN PLACE SNOW TO WATER RATIOS ARE 
EXTREMELY HIGH...BETWEEN 20-30:1. 

JET STREAK ROUNDING THE BASE OF THE TROUGH IS EVIDENT WITH
ENHANCEMENT IN IR SATELLITE IMAGERY AND THE ASSOCIATED VORT MAX
CIRCULATING JUST BEHIND IT. THIS WILL INDUCE PERIODS OF HEAVY
SNOWFALL THROUGH THE NIGHT AND INTO THIS MORNING...MAINLY THROUGH
THE SIERRAS BUT ALSO MODERATE SNOWFALL RATES IN WESTERN NV. AM
ANTICIPATING MORE SNOW ACCUMULATION THAN PREVIOUSLY FORECAST
INCLUDING ACROSS THE RENO/SPARKS/CARSON CITY METRO AREA. UP TO A
FOOT OF SNOW IS POSSIBLE ON THE VALLEY FLOOR BY MONDAY AFTERNOON.

AS THE UPPER LOW ROTATES INTO ERN CA AND WRN NV...SNOWFALL WILL
CONTINUE ACROSS MUCH OF THE CWA THROUGHOUT THE DAY...WITH GREATER
SNOWFALL TOTALS NOW EXPECTED THROUGH MINERAL COUNTY THAN
PREVIOUSLY FORECAST. THEREFORE...WILL BE ADDING THIS COUNTY INTO
THE WINTER STORM WARNING THIS MORNING. ALL OTHER WINTER HIGHLIGHTS
WILL BE CONTINUED...MANY OF WHICH WILL BE UPDATED FOR HIGHER SNOW
TOTALS. DETAILS ON THE WINTER WARNINGS AND ADVISORIES CAN BE FOUND
IN THE RNOWSWREV PRODUCT ON OUR WEB SITE AT WEATHER.GOV/RENO.

ONCE THE TROUGH AXIS SWINGS THROUGH THE AREA THE MOISTURE AND
DYNAMICS WILL QUICKLY END WITH SNOW TAPERING OFF ACROSS NORTHERN
WASHOE COUNTY LATE THIS AFTERNOON AND ACROSS THE REST OF THE ZONES
BY 10 PM. 

THE COLD AIR MASS WILL REMAIN ENTRENCHED OVER THE AREA TUESDAY AND
WEDNESDAY WITH HIGHS STRUGGLING TO GET OUT OF THE 20S EVEN IN
VALLEY LOCATIONS. CLEARING SKIES COMBINED WITH SNOW COVER AND
LIGHT WINDS WILL ALLOW FOR MAXIMUM RADIATIONAL COOLING TUESDAY AND
WEDNESDAY MORNINGS. LOWS WILL BE IN THE SINGLE DIGITS IN THE
WARMEST LOCATIONS WITH WIDESPREAD BELOW ZERO TEMPERATURES
EXPECTED. DF

.LONG TERM...THURSDAY THROUGH SUNDAY...
MADE A FEW MINOR CHANGES TO THE EXTENDED THIS FORECAST CYCLE AS 
MODELS APPEAR TO BE COMING INTO BETTER AGREEMENT AROUND THE 
FRIDAY/SATURDAY TIME FRAME. HOWEVER...MOST OTHER TIME FRAMES WITHIN 
THE EXTENDED PERIOD DO NOT SHOW ENOUGH AGREEMENT TO WARRANT MAKING 
BIG CHANGES TO THE FORECAST.

EARLIER MODELS WERE BRINGING A MODESTLY IMPRESSIVE SYSTEM INTO THE 
SIERRA AS EARLY AS WEDNESDAY NIGHT BUT HAVE BEEN BACK PEDALING A BIT 
FOR ABOUT 24 HOURS NOW WITH THE STRENGTH AND TIMING OF THAT SYSTEM. 
GFS NOW APPEARS TO BE A BIT OF AN OUTLIER AS IT WASHES OUT THE 
SYSTEM ALMOST COMPLETELY BY THURSDAY. ECMWF IS STILL RATHER 
AGGRESSIVE AND GEFS ENSEMBLE QPF > 0.10 PROBABILITY REMAINS AROUND 
50%. HOWEVER...THERE IS QUITE A BIT OF SPREAD AMONG MOST OF THE 
INDIVIDUAL GEFS ENSEMBLE MEMBERS. THUS AM A BIT RELUCTANT TO REDUCE 
POPS IN LINE WITH GFS OR INCREASE POPS IN LINE WITH ECMWF. WILL SHOW 
A MINOR REDUCTION. WILL HOLD ON TO MAINLY CHANCE POPS FOR MOST OF 
THE AREA WITH HIGHER POPS IN THE SIERRA. 

FEEL A BIT MORE CONFIDENT ABOUT THE NEXT SYSTEM ALTHOUGH SOME GEFS 
ENSEMBLE MEMBERS ARE OUT OF LINE WITH THE OPERATIONAL MODELS. 
DETERMINISTIC GFS AND ECMWF BOTH BRING RATHER HIGH QPF INTO THE 
SIERRA SATURDAY...WITH GFS A BIT FASTER. ECMWF HAS TRENDED MUCH 
WETTER THAN GFS RECENTLY AND BOTH MODELS HAVE SHOWN A TENDENCY TO 
PRODUCE TOO MUCH QPF THIS FAR OUT. AM NOT INCLINED TO REALLY RATCHET 
UP POPS ON DAY 6 TOO MUCH...BUT WILL SHOW A BIT OF AN INCREASE IN 
THE SIERRA WHERE FORCING WILL BE BETTER. SNOW LEVELS A BIT TRICKY 
WITH THIS ONE AS WELL. WILL SHOW A BIT OF A RISE FROM PREVIOUS 
FORECAST...BUT NOT TOO HIGH. THIS STORM SYSTEM HAS POTENTIAL TO 
PRODUCE RAIN EAST OF THE SIERRA IN THE WRN NV VALLEYS...BUT RIGHT 
NOW IT IS FAR TOO EARLY TO TALK AMOUNTS OR POSSIBLE FORECAST 
IMPLICATIONS. MLF  

&&

.AVIATION...STRONG COLD FRONT ORIENTED FROM SW TO NE ACROSS AREA 
WILL GRADUALLY SHIFT SOUTHEAST THROUGH 03Z. CONDITIONS WILL 
GRADUALLY IMPROVE AS FRONT SLOWLY EXITS. WIDESPREAD VFR SHOULD 
DEVELOP AFTER 03Z.

FOR KRNO...IFR/LIFR CIGS/VIS THRU 20Z THEN IMPROVING TO MVFR. EXPECT 
VFR CIGS/VIS BY 00Z CONTINUING OVERNIGHT. WINDS LIGHT NORTHEAST THRU 
THE STORM. SNOW WILL CONTINUE TO ACCUMULATION ON RUNWAYS AS RATES 
WILL BE NEAR AN INCH...POSSIBLY 2 INCHES PER HR. 

KLOL...SOME IFR/CIGS VIS THRU 19Z THEN VFR AFTER 22Z. IF SKIES 
CLEAR...FZFG POSSIBLE AFT 08Z TONIGHT...CHC ABOUT 30 PCT. WALLMAN/DK2

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER STORM WARNING UNTIL 7 PM PST THIS EVENING FOR NVZ001>004.

     WINTER WEATHER ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR NVZ005.

CA...WINTER STORM WARNING UNTIL 7 PM PST THIS EVENING FOR CAZ071>073.

     WINTER WEATHER ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR CAZ070.

&&

$$

HTTP://WEATHER.GOV/RENO