Winter Storm Watch 2, NWS Reno, NV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
300 AM TUE NOV 30 2005

.SHORT TERM...
UPPER LOW NEAR 40N 145W AND ITS SUB TROPICAL MOISTURE TAP WILL PHASE
WITH TROUGH DROPPING OUT OF THE GULF OF ALASKA TODAY.  AHEAD OF THE
TROUGH A POTENT SURFACE LOW WILL DEVELOP NEAR 40N 130W AND RACE
TOWARD THE NORTHERN CALIFORNIA COAST TONIGHT. HIGH CLOUDS ARE
STARTING TO SPREAD OVER NORTHERN CALIFORNIA AND WILL SEE INCREASING
CLOUDS THROUGH THE DAY FOR MOST OF WESTERN NEVADA.

ABUNDANT MOISTURE ADVECTION INTO THE SIERRA WILL PRODUCE A
SIGNIFICANT PRECIPITATION EVENT WEDNESDAY NIGHT THROUGH FRIDAY
MORNING.  SNOW LEVELS ARE IN QUESTION ONCE AGAIN AND WILL BE THE
MAIN PROBLEM THE NEXT COUPLE DAYS FOR DETERMINING WHERE WARNING
LEVEL SNOW ACCUMULATIONS WILL FALL.  SUB TROPICAL TAP AND WARM AIR
ADVECTION SUGGEST SNOW LEVELS WILL START OUT ABOVE 7000 FEET THEN
SLOWLY DROP AS COOLER AIR APPROACHES THE SIERRA.  THIS PUTS MORE
WEIGHT ON USING THE 700 MB TEMPERATURES TO DETERMINE SNOW LEVELS.
HOWEVER...MODELS ALSO SHOW VERY STRONG VERTICAL MOTION WHICH COULD
ACT TO LOWER SNOW LEVELS BY 500-1000 FEET.  WARNING LEVEL
ACCUMULATIONS ARE LIKELY ABOVE 8000 FEET...BUT ACCUMULATIONS BETWEEN
7000 AND 8000 FEET (DONNER PASS AND ECHO SUMMIT) IN THE TAHOE ARE
DIFFICULT TO NAIL DOWN AT THIS TIME.  CURRENT THINKING IS 12 INCHES
OR SO COULD FALL BETWEEN 7000 AND 8000 FEET AROUND THE TAHOE
BASIN...SO WITH THAT DECIDED TO ISSUE A WATCH...WITH FUTURE SHIFTS
GETTING A BETTER HANDLE ON THE SNOW LEVELS.  SEVERAL PASSES IN MONO
COUNTY ARE ABOVE 8000 FEET SO THE DECISION TO ISSUE A WATCH AND
POSSIBLE WARNING IS MUCH EASIER.  SNOW LEVELS COULD DROP BELOW 6500
FEET UNTIL LATE THURSDAY NIGHT SO ACCUMULATIONS BELOW 7000 FEET
SHOULD BE LESS THAN 6 INCHES.  PERIODS OF SPILLOVER INTO WESTERN
NEVADA ARE POSSIBLE...BUT WITH SNOW LEVELS ABOVE MOST OF THE TERRAIN
PRECIP WILL BE RAIN.

WINDS WILL ALSO BE AN ISSUE WITH THIS SYSTEM ON THURSDAY AND HAVE
ISSUED A HIGH WIND WATCH FOR WESTERN NEVADA AND THE EASTERN PORTION
OF ZONE 71.  MODELS SHOWING 700 MB WINDS BETWEEN 60 AND 70 KNOTS SO
RIDGE GUSTS WILL BE AT LEAST 90 MPH.  WESTERN NEVADA VALLEYS HAVE
BEEN MIXED OUT SINCE THE LAST SYSTEM SO STRONG WIND GUSTS ALONG THE
EAST SLOPES OF THE SIERRA ARE A GOOD POSSIBILITY.  MODEL SOUNDINGS
FROM THE GFS SHOWS A FAVORABLE THERMAL PROFILE FOR STRONG WINDS TO
MIX TO THE SURFACE ALONG WITH 40-50 KTS BETWEEN 6000 AND 8000 FEET.
A NICE THERMAL GRADIENT ALSO SETS UP WITH RAIN/SNOW COOLED AIR OVER
THE SIERRA AND DOWNSLOPE WARMING WITH HIGHS IN THE MID  TO UPPER 50S
FOR WESTERN NEVADA.  BRONG

.LONG TERM...SATURDAY THROUGH TUESDAY...
MODELS COMING INTO BETTER AGREEMENT OVER THE EXTENDED PERIOD WITH
NORTHWEST FLOW OVER THE WEEKEND AHEAD OF EASTPAC RIDGE. THEN RIDGE
IS EXPECTED TO BUILD INTO THE REGION EARLY NEXT WEEK. 12Z EURO/GFS
WERE MORE AMPLIFIED FOR THE RIDGE...BUT NOW HAVE BACKED OFF AND HAVE
ONLY A WEAK TO MODERATELY AMPLIFIED RIDGE. DO NOT EXPECT MUCH IN THE
WAY OF PRECIP AND BELIEVE THE GFS IS OVERDONE FOR MON/TUE. WOULD
LIKELY SEE QUITE A BIT OF MID AND HIGH CLOUD COVER NORTHERN HALF
WITH A FLATTER RIDGE AND ANY PRECIP WOULD BE CONFINED TO THE EXTREME
NORTH. FOR TEMPERATURES...WILL GO NEAR NORMAL WITH SOME WEAK
INVERSIONS INTO MON...THEN ABOVE NORMAL BY TUESDAY AS NRN GREAT
BASIN SFC HIGH WEAKENS. AT THIS TIME...FORECAST LEANS TOWARD 00Z
EURO. IN ADDITION... STILL LOOKING AT EARLY DEC 1995 AS AN ANALOG
FOR NEXT WEEK SINCE THE PATTERN THE LAST 3-4 WEEKS HAS BEEN
AMAZINGLY SIMILAR WITH LONGWAVE FEATURES AND TRANSITIONS. THE ANALOG
ALSO SUPPORTS THE EURO SOLUTION BEST. WALLMANN

&&

.AVIATION...
VFR CONDITIONS THROUGH 06 THU BEFORE NEXT SYSTEM ARRIVES. WINDS WILL
INCREASE A BIT OVER THE LEE SIDE VALLEYS BUT REMAIN MODERATE THROUGH
12Z. IN THE SIERRA NEAR TAHOE...EXPECT SOME MVFR CIGS/VIS AFTER 06Z
THU AS RAIN MOVES IN WITH HIGH SNOW LEVELS. WALLMANN

&&

.REV WATCHES/WARNINGS/ADVISORIES...
.NV...WINTER STORM WATCH ABOVE 7000 FEET FOR NVZ002 THURSDAY AND
       THURSDAY NIGHT.
      HIGH WIND WATCH FOR NVZ003-005 THURSDAY AFTERNOON AND EVENING.

.CA...WINTER STORM WATCH ABOVE 7000 FEET FOR CAZ072 THURSDAY AND
       THURSDAY NIGHT.
      WINTER STORM WATCH ABOVE 7500 FEET FOR CAZ073 THURSDAY
       AFTERNOON THROUGH FRIDAY MORNING.
      HIGH WIND WATCH FOR CAZ070-071 THURSDAY AFTERNOON AND EVENING.