Winter Storm Watch 3, NWS Reno, NV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
845 AM PST SAT DEC 17 2005

.UPDATE...
PER INITIAL CALL FROM WFO SACRAMENTO...WILL MATCH THEM WITH A WINTER
STORM WATCH FOR LASSEN-TAHOE FOR SUNDAY INTO SUNDAY EVENING. AS
MENTIONED YESTERDAY...MODELS SEEM TO BE A BIT SLOW AND TOO DRY AT
TIMES WITH THE INITIAL UNDERCUTTING SYSTEMS. THIS WEEKEND
APPEARSBEEN NO WITH BOTH THE NAM/GFS QUITE A BIT WETTER THAN
YESTERDAY FOR SUNDAY. AT THIS POINT...IT LOOKS TO BE HIGH END
ADVISORY/LOW END WARNING POTENTIAL FOR THOSE AREAS. SNOW LEVELS WILL
ALSO START OUT LOW...NEAR 4000 FEET BEFORE RISING TO 6000 FEET LATE
ON SUNDAY. EVEN VALLEY LOCATIONS OF LASSEN COULD SEE LOW END WARNING
SNOW AMOUNTS BEFORE THE CHANGEOVER. TO MATCH THE IDEAS AND THE
POTENTIAL COLD AIR DAMMING THAT CAN OCCUR IN THE SURPRISE
VALLEY...WILL ALSO ISSUE A WATCH FOR NORTHERN WASHOE AND THE SV.
EXPECT ANY HEAVY SNOWS IN WASHOE TO REMAIN NORTH OF GERLACH. IN THE
UPDATE WILL ALSO LOWER SNOW LEVELS MOST ZONES TONIGHT TO ACCOUNT FOR
THE LOWER SNOW LEVELS EXPECTED. WALLMANN

&&

.PREV DISCUSSION...ISSUED AT 304 AM
ACTIVE WEATHER DURING THE SHORT TERM.  NARROW RIDGE NOW OVER THE
WEST COAST IS BEING SQUEEZED BY AN APPROACHING DEEP TROUGH OVER
135W.  A VORT MAX SHOWING UP ON SATELLITE IMAGERY THIS MORNING IS
MOVING TOWARD THE CENTRAL CALIFORNIA COAST AND WILL UNDERCUT THE
NORTHERN PART OF THE RIDGE TODAY.  MODELS ARE SIMILAR IN THEIR
EVOLUTION OF THIS SCENARIO WITH THE ETA...GFS...ECMWF...CANADIAN AND
NOGAPS ALL SHOWING THE SYSTEM OFF THE COAST AT 12Z THIS MORNING.
THE FIRST VORT MAX IS PROGGED TO MOVE THROUGH NORTHERN CALIFORNIA
THIS EVENING.  A SECOND STRONGER SHORTWAVE IS THEN PROGGED TO MOVE
THROUGH THE SAME REGION LATE SUNDAY.

WITH THE APPROACHING SYSTEM WILL CONTINUE WILL A CHANCE OF RAIN AND
MOUNTAIN SNOW FOR THIS AFTERNOON AND EVENING.  SOUTHERLY FLOW WILL
ALLOW FOR GOOD MOISTURE ADVECTION TONIGHT INTO SUNDAY.  THE GFS
ADVECTS PRECIPITABLE WATER VALUES OF BETWEEN 0.25 AND 0.50 INCH INTO
WESTERN NEVADA BY 06Z SUNDAY.  SNOW LEVELS WILL START OUT AROUND
6000 FT TODAY BEFORE LOWERING TO BETWEEN 5000 AND 5500 FT TONIGHT AS
COLD AIR MOVES IN WITH THE FIRST SHORTWAVE.  PRECIP SHOULD TAPER OFF
MONDAY AFTERNOON AS THE SECOND SHORTWAVE MOVES EAST OF THE REGION.

DID NOT MAKE ANY MAJOR CHANGES TO TEMPERATURES FOR TODAY AND
SUNDAY.  TEMPS BOTH DAYS SHOULD BE NEAR BOTH CLIMO AND GUIDANCE WITH
AFTERNOON HIGHS IN THE 40S.  EXPECT A SLIGHT WARM UP ON MONDAY AS
RIDGING BUILDS INTO THE WEST COAST.  OHARA

LONG TERM...TUESDAY THROUGH FRIDAY...
MEDIUM RANGE GUIDANCE IS IN REASONABLY GOOD AGREEMENT FOR AN ACTIVE
WEATHER PATTERN IN THE MEDIUM RANGE. RIDGE AXIS OVER CA-NV TUES IS
EXPECTED TO MOVE EAST TO NEAR THE NV-UTAH BORDER BY WED AS TROF
APPROACHES THE WEST COAST. DESPITE HIGH 500 MB HEIGHTS...PACIFIC
MOISTURE WILL BE TAPPED WITH WIDESPREAD HIGH CLOUDS BOTH DAYS AND A
POSSIBILITY OF LIGHT PRECIP OVER NERN CA AND ALONG THE SIERRA WITH
HIGH SNOW LEVELS ABOVE 7500 FEET. MAX TEMPS ARE EXPECTED TO REACH OR
EXCEED 50 DEGREES

BY WED NIGHT AND THURS THE TROF MOVES INLAND AND WILL BRING PRECIP
AND LOWER SNOW LEVELS TO THE FORECAST AREA. MODEL DATA HAVE SOME
DIFFERENCES IN WHETHER THE SYSTEM MOVES IN AS A NEGATIVE TILT
SHORTWAVE OR A CLOSED LOW BREAKING OFF FROM THE MEAN FLOW WHICH
WOULD MAKE A DIFFERENCE AMOUNT OF COOLING ASSOCIATED WITH THE
PRECIP. THE CURRENT FORECAST WAS FAVORING THE 00Z GFS WHICH WOULD
BRING SNOW DOWN TO AROUND 6000 FEET...BUT THE 06Z GFS WAS WEAKER AND
FARTHER NORTH AND WOULD RESULT IN HIGHER SNOW LEVELS AROUND 7000
FEET AND LOWER QPF.

THIS SYSTEM EXITS THE REGION THURS NIGHT WITH REBUILDING RIDGE ON
FRIDAY BRINGING DRIER AIR MASS TO THE REGION. LIGHT E-NE FLOW WILL
RETURN WHICH WOULD LIMIT WARMING...BUT THE INVERSION IS NOT EXPECTED
TO BE AS STRONG AS IT WAS THIS PAST WEEK. MJD

&&

.AVIATION...
THE FOG AND LOW CLOUD EVENT IS ESSENTIALLY OVER ACROSS THE TAF
POINTS AND TWEB ROUTES. SOME SLIGHTLY REDUCED VISIBILITY TO AROUND 5
MILES IS POSSIBLE BETWEEN 15Z AND 17Z IN PARTS OF WRN NV WITH LOCAL
FOG IN CHURCHILL...MINERAL AND MONO COUNTIES OTHERWISE VFR CONDS ARE
EXPECTED TODAY WITH LOWERING CIGS TONIGHT AND AREAS OF MVFR AND
LOCAL IFR CIGS/VSBY AS LIGHT SNOW SPREADS ACROSS THE REGION. MJD

&&

.REV WATCHES/WARNINGS/ADVISORIES...
.NV...WINTER STORM WATCH NVZ002 6 AM TO 11 PM SUNDAY.
      WINTER STORM WATCH NVZ005 9 AM TO 9 PM SUNDAY.
.CA...WINTER STORM WATCH CAZ070 9 AM TO 9 PM SUNDAY.
      WINTER STORM WATCH CAZ071-072 6 AM TO 11 PM SUNDAY.
&&