Winter Storm Watch 11, NWS Reno, NV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
332 AM PST THU DEC 20 2012

.SHORT TERM...
AN UPPER LOW OFF THE PACIFIC NORTHWEST WILL BEGIN TO INFLUENCE THE
REGION TODAY BY PROVIDING AN INCREASE IN WINDS FOLLOWED BY SNOWFALL
COMMENCING IN THE SIERRA BY FRIDAY MORNING. THE STATIONARY NATURE OF
THE LOW WILL PROVIDE A PROLONGED EVENT THAT WILL PRODUCE PERIODS
OF HEAVY SNOW IN THE SIERRA, GUSTY WINDS AND LIKELY SPILLOVER
PRECIPITATION INTO WESTERN NEVADA BY SATURDAY.

THOSE HEADING INTO THE SIERRA TO START THE HOLIDAY SEASON THIS
WEEKEND SHOULD PREPARE FOR DANGEROUS WINTER CONDITIONS. PERIODS OF
HEAVY SNOW AND STRONG WINDS COULD LEAD TO WHITEOUT CONDITIONS AND
LENGTHY TRAVEL DELAYS. TRAVELERS MAY WANT TO CONSIDER A SECONDARY
ROUTE TO AVOID THE SIERRA PASSES THIS WEEKEND.

AN QUICK OVERVIEW OF UPDATES TO THE FORECAST:
* WIND ADVISORIES ISSUED FOR EASTERN LASSEN COUNTY, NORTHERN
  WASHOE COUNTY AND THE SURPRISE VALLEY TODAY.

* WINTER STORM WATCHES ACROSS THE SIERRA HAVE BEEN UPGRADED TO
  WINTER STORM WARNINGS.

* WINTER STORM WATCH HAS BEEN ISSUED FOR THE SIERRA FRONT REGION
  IN WESTERN NEVADA BEGINNING SATURDAY.

WIND: WATER VAPOR SATELLITE IMAGERY SHOWS THE DEEP UPPER LOW
CENTER OFFSHORE OF BRITISH COLUMBIA AND HAS BEGUN TO STREAM MID
AND HIGH LEVEL CLOUDS ACROSS NORTHERN CA AND NORTHERN NV. SURFACE
GRADIENTS HAVE ALSO INCREASED AHEAD OF THE LOW WHICH WILL PRODUCE
GUSTY CONDITIONS ESPECIALLY ACROSS NE CA AND NW NV. WIND GUSTS
UPWARDS OF 50 MPH ARE POSSIBLE ACROSS ADVISORY AREAS WITH UP TO 45
MPH POSSIBLE ACROSS SIERRA VALLEYS AND LEESIDE VALLEYS IN WESTERN
NEVADA. LAKE WIND ADVISORIES ARE CURRENTLY IN EFFECT FOR LAKE
TAHOE AND PYRAMID LAKE. ANOTHER ROUND OF GUSTY WINDS IS EXPECTED
AGAIN BY FRIDAY NIGHT INTO SATURAY MORNING AS THE NEXT JET IMPULSE
PUSHES INTO THE AREA.

PRECIPITATION: ATTENTION THEN TURNS TO THE FIRST IN A SUCCESSION
OF MOISTURE PLUMES THAT WILL PROVIDE THE SIERRA WITH SIGNIFICANT
SNOWFALL. WINTER STORM WARNINGS GO IN EFFECT FRIDAY MORNING FROM
LASSEN COUNTY THROUGH THE TAHOE BASIN WITH MONO COUNTY BEGINNING
LATER IN THE AFTERNOON. THE FIRST ROUND OF MOISTURE WILL HAVE THE
POTENTIAL TO DROP ABOUT A FOOT AND A HALF OF SNOW ACROSS HIGHER
SIERRA TERRAIN. SNOWLEVELS WILL BE LOW ENOUGH TO ACCUMULATE SNOW
AT LAKE LEVEL AND ACROSS ALL PASSES...IMPACTING MOTORISTS
ATTEMPING TRAVEL ACROSS THE SIERRA. A SECOND (0.8") MOISTURE PLUME
FOLLOWS IMMEDIATELY BEHIND BY EARLY SATURDAY MORNING WHICH MAY
PROVIDE AN ADDITIONAL 2+ FEET OF ACCUMULATION ACROSS THE SIERRA
THROUGH EARLY SUNDAY MORNING. MODEL SOUNDINGS ACROSS WRN NV SHOW A
MODERATELY UNSTABLE AND MOIST VERTICAL PROFILE SATURDAY WHICH
WILL COUPLE WITH STRONG WINDS ALOFT AND A FRONTAL PASSAGE. THIS
WILL PROVIDE A GOOD POTENTIAL FOR SPILLOVER PRECIPITATION IN THE
FOOTHILLS ACROSS WESTERN NEVADA WITH ACCUMULATIONS POSSIBLE AT
VALLEY FLOORS BY SATURDAY. AS SUCH, AS WINTER STORM WATCH HAS BEEN
ISSUED FOR THE SIERRA FRONT BEGINNING SATURDAY THROUGH THE END OF
THE WEEKEND. FUENTES

.LONG TERM...SUNDAY THROUGH WEDNESDAY...

OVERALL PATTERN HAS CHANGED LITTLE IN THE LEAD UP TO CHRISTMAS DAY.
DEEP COLD LOW OVER THE NORTHEAST PACIFIC WILL DIRECT THE JET AND ONE
FINAL WAVE INTO THE SIERRA AND WESTERN NEVADA EITHER SUNDAY OR
SUNDAY NIGHT.  RIDGE WILL BUILD OVER THE SIERRA BEHIND THE DEPARTING
SYSTEM WITH STRONG SURFACE INVERSIONS AND COLD AND DRY CONDITIONS
FOR CHRISTMAS DAY.

TRAVEL LIKELY TO REMAIN DANGEROUS IN THE SIERRA DUE TO HEAVY SNOW
AND STRONG WINDS SUNDAY AND SUNDAY NIGHT.  ANYONE WITH PLANS TO
DRIVE OVER THE SIERRA PASSES NEEDS TO CONSIDER AN ALTERNATE ROUTE,
OR DELAYING TRAVEL UNTIL MONDAY AFTERNOON.

MODELS CONTINUE TO TAP INTO A PLUME OF MOISTURE STRETCHING BACK TO
THE INTERNATIONAL DATELINE.  IN THE 00Z MODELS, THE PLUME IS LINING
UP WITH A UPPER WAVE AND SURFACE LOW AS IT REACHES THE SIERRA.
HEAVY SNOW WILL RESULT IN THE SIERRA WITH SNOW SPREADING INTO
WESTERN NEVADA.  SNOW LEVELS DO REMAIN IN QUESTION FOR WESTERN
NEVADA ON SUNDAY, BUT SHOULD REMAIN NEAR AND BELOW 5000 FEET.
DESPITE WARM AIR ADVECTION WITH THE MOISTURE PLUME, THERE ISN'T
GOING TO BE ENOUGH MIXING TO WARM THE VALLEYS THIS KEEPING SNOW
LEVELS ON THE LOW SIDE.

SNOW ACCUMULATIONS REMAIN IN QUESTION ACROSS THE WESTERN NEVADA
VALLEYS AS THIS SYSTEM MAY MOVE THROUGH DURING THE DAY LIGHT HOURS.
THIS WOULD LIKELY LIMIT OR PERHAPS PREVENT SNOW FROM STICKING TO
ROADS ON VALLEY FLOORS, ESPECIALLY IN RENO-SPARKS.  HOWEVER THE
ECMWF BRINGS THE SYSTEM THROUGH SUNDAY EVENING/SUNDAY NIGHT WHICH IS
MUCH MORE FAVORABLE TO SNOW ON VALLEY FLOORS.  EVEN IF THE SYSTEM
PASSES THROUGH DURING THE DAY SUNDAY...DO FEEL CONFIDENT IN SEVERAL
INCHES OF SNOW ABOVE 5000 FEET IN THE LOCATIONS AROUND RENO, CARSON,
MINDEN, AND VIRGINIA CITY.

RIDGE BUILDS IN CHRISTMAS EVE AND CHRISTMAS DAY LEADING TO STRONG
INVERSIONS TRAPPING COLD AIR IN THE VALLEYS.  HIGHS CHRISTMAS DAY
SHOULD BE LIMITED TO THE LOW 30S, PERHAPS REMAINING BELOW FREEZING
ACROSS WESTERN NEVADA WITH FRESH SNOW COVER.  WEDNESDAY MORNING LOWS
WILL ALSO DIP INTO THE SINGLE DIGITS MOST LOCATIONS.

MID WEEK APPEARS TO BE DRY AS THE RIDGE HOLDS ITS PLACE OVER THE
INTERMOUNTAIN WEST AS TROUGH DEVELOPS NEAR 130-140W. THE GFS HAS A
BIAS OF PUSHING ENERGY INTO RIDGES TO QUICKLY.  MOST GUIDANCE SPLITS
PACIFIC MOISTURE AS IT HITS THE RIDGE WITH A LOW DEVELOPING OFF THE
CALIFORNIA COAST, WHICH MAY MOVE ONSHORE DEC 28 OR 29.  BRONG

&&

.AVIATION...

INCREASING CLOUDS AND WINDS TODAY AS THE FIRST IN A SERIES OF
PACIFIC SYSTEMS REACHES THE WEST COAST. PEAK SURFACE GUSTS OF 30 TO
40 KTS WITH THE PRIMARY WIND DIRECTION FROM THE SOUTH.  RIDGE TOP
WINDS WILL EXCEED 50 KTS LATER TODAY.

SNOW WILL START TO PUSH INTO THE NORTHERN SIERRA AFTER 00Z FRIDAY
AND REACHING THE TAHOE TERMINALS BY 18Z FRIDAY. IFR-MVFR CONDITIONS
LIKELY TO PERSIST AT KTRK AND KTVL FRIDAY AFTERNOON THROUGH SUNDAY
OR SUNDAY NIGHT.  ACROSS WESTERN NEVADA PERIODS OF RAIN/SNOW ARE
POSSIBLE SATURDAY AFTERNOON/EVENING AND AGAIN SUNDAY AND/OR SUNDAY
NIGHT.  BRONG

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WIND ADVISORY FROM 10 AM THIS MORNING TO 10 PM PST THIS EVENING
     NVZ005.

     LAKE WIND ADVISORY UNTIL 6 AM PST FRIDAY FOR LAKE TAHOE IN
     NVZ002.

     WINTER STORM WARNING FROM 6 AM FRIDAY TO 4 AM PST MONDAY NVZ002.

     WINTER STORM WATCH FROM SATURDAY MORNING THROUGH LATE SUNDAY
     NIGHT NVZ003.

     LAKE WIND ADVISORY UNTIL 7 PM PST THIS EVENING FOR PYRAMID LAKE
     IN NVZ004.

CA...WIND ADVISORY FROM 10 AM THIS MORNING TO 10 PM PST THIS EVENING
     CAZ070-071.

     WINTER STORM WARNING FROM 4 AM FRIDAY TO 10 PM PST SUNDAY CAZ071.

     WINTER STORM WARNING FROM 4 PM FRIDAY TO 4 AM PST MONDAY CAZ073.

     LAKE WIND ADVISORY UNTIL 6 AM PST FRIDAY FOR LAKE TAHOE IN
     CAZ072.

     WINTER STORM WARNING FROM 6 AM FRIDAY TO 4 AM PST MONDAY CAZ072.

&&

FOR MORE INFORMATION FROM THE NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/RENO (ALL LOWER CASE)