Strong Wind in Nevada, December 21 to 22, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
859 PM PST SUN DEC 21 2008

.UPDATE...
EVENING SOUNDING FROM REV SHOWED A CRITICAL LAYER JUST ABOVE H700
WITH WIND SPEEDS IN THE 45 KT RANGE. FORECAST SOUNDINGS FROM BOTH
THE GFS AND NAM SHOW THIS LAYER PERSISTING AND LOWERING SLIGHTLY
THROUGH THE NIGHT WITH WINDS INCREASING TO 50 TO 60 KTS WITHIN
THE LAYER. RIDGE GUSTS WEST OF THE SIERRA FRONT HAVE INCREASED TO
60 MPH. WITH THIS STABLE LAYER ALREADY ESTABLISHED THINK WINDS
WILL GUST HIGHER LATER TONIGHT ALONG THE SIERRA FRONT INTO MONO
COUNTY. 30 AGL WINDS FROM NAM INDICATE UP TO 60 KTS OVER THE RGN
BUT THESE APPEAR A BIT TOO STRONG. GFS 30 AGL WINDS ARE MUCH
LOWER. AS IS TYPICAL NAM MAY BE OVER DOING THESE WINDS AS IT TENDS
TO DEVELOP TOO MUCH SHADOWING IN THE LEE OF THE SIERRA AND THUS
STRONGER DOWN SLOPE WINDS WHILE GFS TENDS TO UNDER DO THE WINDS.
TAKING A MEAN NUMBER WOULD PRODUCE WIND GUSTS AROUND 50 MPH FROM
THE RENO ARE SOUTH INTO MONO COUNTY LATE TONIGHT AND INTO EARLY
MONDAY UNTIL COLD FRONT PASSES THROUGH THE RGN. WHILE A FEW AREAS
WILL NOT SEE THESE WINDS...LOCALLY WINDY AREAS COULD REACH GUSTS
UP TO 55 MPH. WILL ISSUE WIND ADVISORY FOR NVZ003 AND CAZ073
ENDING WITH PASSAGE OF THE FRONT EARLY MONDAY MORNING NORTH TO
LATE MONDAY MORNING SOUTH.

OVERNIGHT TEMPS NOT FALLING VERY FAST AND HAVE MADE A FEW
ADJUSTMENTS FOR THESE IN FORECAST GRIDS BUT TEMPS SHOULD FALL TO
NEAR FORECAST LOWS SHORTLY AFTER THE FRONT PASSES. SOME RAIN STILL
BEING REPORTED UP TO AROUND 6000 FEET BY LOCAL SPOTTERS AND HAM
RADIO OPERATORS. WILL ALSO MAKE ADJUSTMENTS FOR THIS IN WORDING
BUT WITH PASSAGE OF FRONT FROM NORTH TO SOUTH SNOW LEVELS WILL
FALL TO VALLEY FLOORS. ACCUMULATIONS MIGHT BE AN ISSUE AS SNOW
LEVELS ARE A BIT HIGHER THAN EXPECTED NOW AND FIRST ROUND PCPN IS
TAPERING OFF. ANOTHER ROUND OF PCPN SHOULD MOVE IN WITH THE FRONT
LATE TONIGHT AND GIVEN THAT SNOW LEVELS WILL BE FALLING THERE
SHOULD BE A QUICK BURST OF ACCUMULATING SNOWS SOMETIME FROM
MIDNIGHT UNTIL AROUND DAYBREAK. SO DO NOT PLAN ANY CHANGES TO
GOING WINTER WEATHER ADVISORIES. MLF

&&

.PREVIOUS DISCUSSION...ISSUED 300 PM PST SUN DEC 21 2008...
SHORT TERM...
FIRST WAVE OF THE NEXT SYSTEM HAS MOVED INTO THE REGION WITH THE
MAIN MOISTURE PLUME GRADUALLY SLIDING SOUTH DOWN THE SIERRA TOWARD
MONO COUNTY. THERE WILL BE LULL IN THE ACTION BEHIND THIS WAVE
WITH PRECIP IN THE SIERRA LIGHTENING UP BEFORE THE MAIN COLD
FRONTAL BAND PUSHES THROUGH THE REGION TONIGHT. A FEW INCHES OF
SNOW IS POSSIBLE WITH THE FIRST WAVE BUT THE BRUNT OF THE
PRECIPITATION WILL COME WITH THE COLD FRONT. CURRENT THINKING HAS
NOT CHANGED WITH THIS SYSTEM AND STILL EXPECTING AROUND A FOOT OR
SO OF SNOW ABOVE 7000 FEET IN THE TAHOE BASIN WITH LESSER AMOUNTS
OVER LASSEN/PLUMAS COUNTIES AND SIERRA VALLEYS INCLUDING LAKE
TAHOE. THE SIERRA OF MONO COUNTY COULD RECEIVE 6 TO 10 INCHES
ABOVE 7000 FEET BUT LOOKS TO BE BELOW ADVISORY LEVELS. NORTHERN
WASHOE/SURPRISE VALLEY SHOULD SEE SEVERAL INCHES OF SNOW WITH THE
FRONT TONIGHT WHICH LOOKS TO PUSH SOUTH AND THROUGH THE RENO AREA
AROUND 4AM. JET DYNAMICS ARE SOMEWHAT FAVORABLE IN TRYING TO PUSH
LIGHT PRECIP OVER THE SIERRA INTO THE RENO/CC AREA AROUND
6Z...WHICH WOULD FALL AS RAIN...BUT THE BEST CHANCES OF RECEIVING
PRECIP WILL BE RAIN CHANGING TO SNOW WITH THE COLD FRONT. SNOW
LEVELS ARE CURRENTLY AROUND 6000 FEET NORTH TO AROUND 7000 FEET
SOUTH AND WILL PLUMMET TO ALL VALLEY FLOOR LOCATIONS LATER TONIGHT
INTO TOMORROW MORNING AS 700 MB TEMPS DROP TO -12 TO -14C. IN THE
LEE OF THE SIERRA SNOWFALL IS NOT EXPECTED TO ACCUMULATE TO MUCH
MORE THAN AN INCH AND WILL BE LOCALIZED.

WINDS AHEAD OF THE FRONT DO LOOK TO BE BREEZY AND WILL LIKELY GUST
TO 45 MPH. WINDS COULD BE SLIGHTLY STRONGER OVER MONO COUNTY LATER
TONIGHT INTO TOMORROW MORNING AS THE JET STRENGTHENS AS IT
APPROACHES THE SOUTHERN SIERRA. A WIND ADVISORY IS NOT OUT OF THE
REALM OF POSSIBILITY FOR MONO COUNTY.  SIERRA RIDGE WINDS ARE STILL
EXPECTED TO GUST TO AROUND 100 MPH AS 700 MB WINDS INCREASE TO
OVER 50 KTS.

AFTER THE FRONT PASSES...SCATTERED SNOW SHOWERS ARE EXPECTED MONDAY
AFTERNOON. ANOTHER WEAK FAST WAVE WILL MOVE INTO THE SIERRA IN
NORTHWEST FLOW MONDAY NIGHT AND COULD PRODUCE SEVERAL INCHES OF
ADDITIONAL SNOW IN THE SIERRA WITH LOCALIZED UP TO AN INCH IN VALLEY
LOCATIONS.

TUESDAY IS EXPECTED TO BE MAINLY DRY AS THE NEXT SYSTEM DROPS DOWN
THE CA COAST.  THIS LOW SHOULD BE FAR ENOUGH WEST TO KEEP THE
MAIN PRECIP BAND WELL WEST OF THE SIERRA TUESDAY NIGHT. THERE IS
STILL EXPECTED TO BE SOME LIGHT SNOW SHOWERS OVER THE SIERRA AND
INTO WESTERN NEVADA DURING THIS TIME BUT ACCUMULATIONS WILL BE VERY
MINIMAL. THE LOW WILL THEN SWING INLAND WEDNESDAY AND DEPENDING ON
TRACK COULD GIVE THE SOUTHERN SIERRA SOME MODEST
SNOWS...PARTICULARLY OVER MONO COUNTY WHERE POTENTIALLY SIX INCHES
OF SNOW COULD FALL IN THE HIGH SIERRA. THIS FAST MOVING LOW SHOULD
BE SOUTH AND EAST OF THE AREA BY LATE WEDNESDAY AFTERNOON AS THE
NEXT STORM APPROACHES.  MILNE

LONG TERM...CHRISTMAS DAY THROUGH SUNDAY...
MEDIUM RANGE MODELS ARE CONSISTENT IN BRINGING ANOTHER COLD FRONT
THROUGH THE SIERRA AND WESTERN NEVADA ON CHRISTMAS DAY. THE EC AND
CANADIAN ARE SHARPER WITH THE ASSOCIATED TROUGH AND A BIT FASTER
THAN THE GFS...AND ALSO DEPICT A STRONG NW-SE ORIENTED JET WHILE THE
GFS BRINGS IN A MORE FAVORABLE WNW-ORIENTED JET ACROSS THE SIERRA.
THE LATEST NAM SUPPORTS THE GFS ORIENTATION SO THE GENERAL CONCEPT
OF THE GFS WAS USED FOR THE CHRISTMAS PERIOD.

ALL MODELS ARE GENERATING BETWEEN 1/2 INCH TO AN INCH OR MORE QPF
FOR THE SIERRA MAINLY AFTER MIDNIGHT CHRISTMAS EVE TO LATE AFTERNOON
CHRISTMAS DAY.  THE ASSOCIATED COLD FRONT MOVES THROUGH THE AREA
DURING THE DAY SO WE WILL HAVE STRONG RIDGE GUSTS AND SURFACE WINDS
WHICH WILL INCREASE THE NIGHT OF CHRISTMAS EVE AND CONTINUE
CHRISTMAS DAY. IT WILL BE COLD ENOUGH FOR SNOW ALL AREAS. IF WE STAY
CONSERVATIVE ON QPF AMOUNTS...WE COULD STILL SEE UP TO 6 INCHES AT
LAKE LEVEL WITH OVER A FOOT AT HIGHER ELEVATIONS OF THE SIERRA FROM
TAHOE SOUTH INTO MONO COUNTY. LASSEN COUNTY AND NORTHERN WASHOE
SHOULD SEE SEVERAL INCHES. FOR THE RENO-CARSON AREAS THE ORIENTATION
OF THE JET WILL BE CRITICAL. IF IT COMES IN CLOSE TO THE GFS
SOLUTION THIS AREA WOULD BE UNDER THE FAVORABLE LEFT EXIT REGION FOR
FORCING. ALSO THE FRONTOGENESIS LOOKS DECENT WITH THIS SYSTEM. WILL
HAVE TO LOOK AT FUTURE RUNS...RENO-CARSON COULD BE SHADOWED OUT AND
SEE MORE WIND THAN SNOW EXCEPT FOR A QUICK INCH WITH THE FRONT...OR
WE COULD PICK UP A COUPLE OF INCHES DUE TO FAVORABLE DYNAMICS.

THURSDAY NIGHT THROUGH FRIDAY WE WILL SEE SCATTERED SNOW SHOWERS
MAINLY IN THE SIERRA UNDER COLD CYCLONIC FLOW ALOFT. AS THE
CHRISTMAS SYSTEM MOVES RAPIDLY EAST THE UPPER FLOW FLATTENS OUT
HEIGHTS INCREASE THROUGH THE WEEKEND AND THE JET IS PUSHED NORTH
INTO THE PACNW. THIS WOULD KEEP OUR AREA GENERALLY DRY FOR THE
WEEKEND WITH ANY CHANCE OF SHOWERS CONFINED TO FAR NORTHEAST CA AND
THE OREGON BORDER.

TEMPERATURES WILL CONTINUE BELOW SEASONAL NORMALS BUT WILL MODERATE
CLOSER TO NORMAL FOR THE WEEKEND UNDER BUILDING HEIGHTS. EXPECT
FRIDAY TO BE THE COLDEST DAY BEHIND THE FRONT. WARMING ALOFT FOR THE
WEEKEND WILL CREATE STRONG INVERSIONS WITH COLD VALLEY TEMPERATURES
AND MUCH WARMER READINGS AT HIGHER ELEVATIONS. LIGHT WINDS WILL
INHIBIT MIXING AND SLOW THE WARMING IN VALLEY LOCATIONS. JAH

AVIATION...
KTVL/KTRK - HEAVIEST PRECIP WILL OCCUR AHEAD OF AND ALONG THE FRONT
OVERNIGHT. EXPECT 6 INCHES OF SNOW THOSE LOCATIONS WITH IFR
CIGS/VSBY ROUGHLY 08Z-15Z WITH CONDITIONS IMPROVING AFTER 18Z.

KRNO...BEST CHANCE FOR SNOW WILL BE FOR AN HOUR OR SO CENTERED
AROUND 12Z MON. EXPECT SOME SURFACE GUSTS TO 35KTS AFTER 06Z AND
DIMINISHING BY 14Z. THERE COULD BE A FEW HOURS AROUND 06Z WITH UPPER
WINDS WSW AT 50KTS WHILE SURFACE WINDS WILL BE SW OR MAY BACK TO SSE
AT 15-20KT.

KLOL...LIGHT RAIN WITH MVFR CIGS 00Z-03Z WITH A BREAK AFTER
THAT..THEN SNOW WITH MVFR CIGS/VIS AGAIN AROUND 15Z MON. JAH

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER WEATHER ADVISORY UNTIL 7 AM PST MONDAY FOR NVZ002.

     WIND ADVISORY UNTIL 7 AM PST MONDAY FOR NVZ003.

CA...WINTER WEATHER ADVISORY UNTIL 4 AM PST MONDAY FOR CAZ071.

     WIND ADVISORY FROM 1 AM TO 10 AM PST MONDAY FOR CAZ073.

     WINTER WEATHER ADVISORY UNTIL 7 AM PST MONDAY FOR CAZ072.

&&

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