Strong Wind and Winter Weather in Nevada, December 14 to 15, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
310 PM PST MON DEC 13 2010

.SHORT TERM...

STRONG UPPER LEVEL JET AND COLD FRONT IS EXPECTED TO MOVE INTO
NORTHERN CA AND OREGON TONIGHT AND INTO TUESDAY...BRINGING SOME BIG
CHANGES TO THE WEATHER ACROSS THE REGION IN THE SHORT TERM.

THIS FAST MOVING SYSTEM WILL BEGIN TO SPREAD PRECIPITATION INTO THE
NORTHERN SIERRA TUESDAY MORNING AND ACROSS THE AREA THROUGH TUESDAY
EVENING. THE SNOW LEVELS WILL START OUT FAIRLY HIGH AROUND 7000-7500
FEET...BUT BY TUESDAY EVENING THESE SNOW LEVELS ARE EXPECTED TO DROP
TO AROUND 5000-6000 FEET...AS THE COLD FRONT PUSHES THROUGH. LATEST
NAM FORECAST IS ABOUT 3-6 HOURS FASTER THAN THE GFS/ECMWF...SO
PUSHED THE TIMING OF THE WINTER WX ADVISORY UP TO 15Z TUESDAY
MORNING. WILL HAVE TO KEEP A CLOSE EYE ON THE NAM...AS IT SHOWS MUCH
HIGHER QPF THAN THE GFS/ECMWF. KEPT CLOSER TO THE ONGOING
FORECAST...CLOSER TO THE GFS/EC SOLUTION.

THE HIGHEST IMPACT AREAS WILL BE THE SIERRA PASSES AROUND LAKE TAHOE
ABOVE 7000 FEET...WHERE WE COULD SEE 6 TO 12 INCHES OF SNOW BY
WEDNESDAY MORNING. WE ARE ALSO CALLING FOR THE POTENTIAL OF UP TO 18
INCHES IN THE HIGHEST ELEVATIONS ALONG THE SIERRA CREST BY TUESDAY
MORNING. WITH SNOW LEVELS HIGH INITIALLY...DECIDED TO KEEP TOTAL
SNOW AMOUNTS DOWN AT LAKE LEVEL PRETTY TAME. SHOULD ONLY SEE AROUND
3 TO 4 INCHES AT LAKE LEVEL...WITH UP TO 6 INCHES POSSIBLE ALONG THE
WEST SHORE. ISSUED A WINTER WEATHER ADVISORY FOR THE LAKE TAHOE
BASIN TUESDAY MORNING THROUGH LATE TUESDAY NIGHT...ALTHOUGH THE
HEAVIEST SNOWFALL WILL BE WITHIN A 6 HOUR PERIOD TUESDAY AFTERNOON
AND EVENING...WHEN THE COULD SEE SOME LOCALIZED HEAVY SNOW AMOUNTS
IN THE SIERRA IN THE HIGHER ELEVATIONS OF PLUMAS AND SIERRA
COUNTIES...BUT LEFT THESE OUT OF THE ADVISORY SINCE ITS ONLY A SMALL
PORTION OF THE ZONE. ALSO MONO COUNTY WEST OF BRIDGEPORT MAY SEE
SOME LOCALIZED HIGHER AMOUNTS AS WELL.

AS FAR AS PRECIP AMOUNTS IN WESTERN NV...WE WILL SEE GENERALLY
BETWEEN 0.1" AND 0.25" OF RAIN DOWN TO THE LOWER VALLEYS. WE COULD
SEE SOME HEAVIER AMOUNTS FROM RENO NORTHWARD ON TUESDAY AFTERNOON
AND EVENING AS STRONG UPPER JET DIVERGENCE AND LOW LEVEL
FRONTOGENESIS SETS UP OVER THE AREA. LUCKILY SNOW LEVELS NORTH OF
RENO WILL BE ABOVE 6000 FEET...SO ANY IMPACTS WILL BE MINIMAL. WILL
HAVE TO KEEP AN EYE ON THE FORCING HERE AS MODELS HAVE BEEN TRENDING
HIGHER QPF NORTH OF I-80. SNOW LEVELS WILL FALL TO BETWEEN 5500-5000
FEET BY WEDNESDAY MORNING...BUT AS THE FORCING TAILS OFF SO WILL THE
CHANCES FOR ANY ACCUMULATING SNOW IN WESTERN NV.

AS FOR THE WINDS...THE 700 MB WINDS WILL INCREASE SIGNIFICANTLY OVER
THE NEXT 12 HOURS...WITH AROUND 55KTS EXPECTED BY 12Z TUES. MODELS
ARE SHOWING SOME PRETTY GOOD MIXING IN THE LOWER LEVELS...ALONG WITH
POTENTIAL FOR DOWNSLOPING WINDS. WIND GUSTS TO 45KTS ARE EXPECTED TO
MIX DOWN TO THE SURFACE IN THE AFTERNOON. HAVE ISSUED WIND
ADVISORIES FOR TUESDAY MAINLY ALONG THE SIERRA FRONT...FROM THE
OREGON BORDER SOUTH INTO MONO COUNTY CA. RIDGE WINDS WILL INCREASE
IN THE SIERRA TO OVER 100 MPH AS THE JET MOVES OVERHEAD. NOT
EXPECTING ANY HIGH WINDS AT THIS TIME...BUT DEFINITELY A SOLID
ADVISORY LEVEL WIND EVENT. WIND PRONE AREAS...ESPECIALLY ALONG
HIGHWAY 395...MAY SEE WIND GUSTS UP TO 65 MPH IN THE AFTERNOON ON
TUESDAY.

FOR WEDNESDAY...WE SHOULD SEE SOME LINGERING SHOWERS THROUGH THE DAY
BUT ACCUMULATING SNOW WILL BE MINIMAL. SHORTWAVE RIDGING WILL BUILD
OVERHEAD ALLOWING FOR SOME DRIER CONDITIONS AND LIGHTER WINDS. OUR
NEXT SYSTEM APPROACHES THE WEST COAST LATE THURSDAY WITH INCREASING
CLOUDS AND CHANCES FOR MORE VALLEY RAIN AND MOUNTAIN SNOW.  HOON

.LONG TERM...FRIDAY THROUGH MONDAY...

LOWERED SNOW LEVELS FRIDAY MORNING...RAISED SNOW LEVELS SLIGHTLY
SATURDAY...AND RAISED LOW TEMPS SATURDAY NIGHT.

PRETTY DECENT BUT BRIEF WARM AIR ADVECTION PATTERN EXPECTED WITH
FRIDAY'S FAST MOVING SYSTEM...MAINLY NORTH OF HIGHWAY 50 PER CURRENT
DETERMINISTIC MODELS. WITH GOOD WARM AIR ADVECTION ON THE ORDER OF
35-50 KTS PERPENDICULAR TO SEVERAL ISENTROPIC SURFACES BETWEEN
750-500 MB I EXPECT A PERIOD OF PRECIP TO HAVE NO PROBLEM SPILLING
OVER INTO PORTIONS OF WESTERN NEVADA FROM THE SIERRA. WITH
UNCERTAINTY AS TO WHERE THE BEST LIFT/WAA FOCUSES I HAVE ONLY UP
POPS SLIGHTLY IN THE BASIN NORTH OF INTERSTATE 80 FOR NOW. ON THE
PRECIP TYPE SIDE...I HAVE LOWERED SNOW LEVELS QUITE A BIT FOR FRIDAY
MORNING IN THE BASIN AS ISOTHERMAL PROFILES ARE DEFINITELY INDICATED
WITH THE GOOD WAA ALOFT AND SOME EASTERLY COMPONENT TO THE LOW LEVEL
WINDS. FOR NOW I HAVE JUST LOWERED IT ENOUGH TO GET RAIN OR SNOW FOR
MANY LOWER VALLEYS NORTH OF HIGHWAY 50...BUT THIS MAY WIND UP BEING
ALL SNOW THROUGH AT LEAST FRIDAY MORNING WITH A COUPLE INCHES OF
SNOW NOT OUT OF THE QUESTION ON LOWER VALLEY FLOORS. ONCE THE WAA
DIMINISHES BY FRIDAY AFTERNOON SNOW LEVELS SHOULD SHOOT UP AND
PRECIP SHOULD BECOME SHOWERY.

LATE FRIDAY NIGHT AND INTO SATURDAY...ANOTHER ROUND OF WAA IS
PROGGED. BY THAT TIME...UNCERTAINTY REALLY REARS INTO UGLY HEAD
ESPECIALLY FOR SNOW LEVELS. THE KEY WILL BE HOW MUCH COLDER AIR WE
CAN FILTER IN BEHIND FRIDAY'S SYSTEM. IF THE SYSTEM IS A BIT
STRONGER AS SHOWN IN THE GFS...WE WILL BE ABLE TO BRING COLDER AIR
INTO NORTHERN NEVADA AS COMPARED WITH THE WEAKER SYSTEM/WARMER AIR
SHOWN IN THE ECMWF AND GEM. THE AIRMASS BEHIND FRIDAY'S SYSTEM WILL
DETERMINE WHETHER WE START WITH SNOW LEVELS NEAR 5000 FEET OR CLOSER
TO 6000-6500 FEET EARLY SATURDAY MORNING DURING THE WAA EPISODE.
FOR NOW I HAVE GONE TOWARD THE HIGHER END AS THE ECMWF AND GEM ARE
ON BOARD WITH A WARMER START...HOWEVER THERE IS NO GUARANTEE THIS
WILL NOT CHANGE IN THE NEXT FEW MODEL RUNS.

BY SATURDAY AFTERNOON...THERE IS EVEN MORE TROUBLE WITH SNOW LEVELS
AS THE GEM/ECMWF ARE MUCH WARMER THAN THE GFS. AT THIS TIME...
SATURDAY LOOKS TO HAVE TO HIGHEST SNOW LEVELS OF THE ENTIRE EXTENDED
WITH THE ECMWF SHOWING SNOW LEVELS AS HIGH AS 8500 FEET BRIEFLY
SATURDAY WITH THE GEM HOLDING IN HIGH SNOW LEVELS INTO SATURDAY
NIGHT. HOWEVER...ONE THING THAT IS NOT IN QUESTION WILL BE
PRECIPITATION FOR THE SIERRA AND PORTIONS OF WESTERN NEVADA WITH A
NICE MOISTURE FEED AND JET STREAK. THE FRIDAY NIGHT THROUGH SATURDAY
NIGHT PERIOD COULD BRING THE HEAVIEST PRECIP AMOUNTS OF THE EXTENDED
PERIOD TO THE SIERRA AND WESTERN NEVADA.

SUNDAY AND MONDAY...A REVIEW OF ENSEMBLE SPAGHETTI PLOTS AND MODELS
SEEMS TO KEEP RELATIVELY COOL AIR ALOFT OVER THE REGION TO KEEP SNOW
LEVELS FROM SOARING TOO HIGH (ABOVE 8000 FEET). HOWEVER...THERE ARE
MANY DISCREPANCIES AMONG MODELS AND ENSEMBLES AS TO THE EXACT
ORIENTATION OF THE FLOW ALOFT. THE GFS AND GEM ARE FLATTER AND MORE
ZONAL FOR COOLER TEMPS ALOFT WHILE THE ECMWF AND ITS ENSEMBLES SEEM
SET ON A DIGGING EASTERN PACIFIC TROUGH AND BRINGING WARMER TEMPS
ALOFT. IN ANY CASE...WE WILL STILL HAVE GOOD CHANCES FOR PRECIP IN
ALL MODELS INTO EARLY NEXT WEEK SO FOLKS SHOULD KEEP AN EYE ON THE
LATEST PRECIP/SNOW LEVEL PROGS AS WE GET CLOSER TO NEXT WEEK.
SNYDER
&&

.AVIATION...

VFR THIS EVENING WITH INCREASING MID AND HIGH LEVEL CLOUDS. WINDS
WILL BEGIN TO INCREASE TUESDAY MORNING WITH GUSTS UP TO 55 MPH IN
THE SIERRA AND EXTREME WESTERN NEVADA AND UP TO 100 MPH OVER SIERRA
RIDGETOPS. THIS WILL LIKELY CAUSE TURBULENCE ACROSS AND DOWNWIND OF
THE SIERRA.

PRECIP WILL START IN THE SIERRA TUESDAY MORNING WITH SNOW LEVELS
AROUND 6.5-7K FT MSL. THE HEAVIEST PRECIP WILL BE IN THE AFTERNOON
AND EVENING AS A COLD FRONT SINKS ACROSS THE AREA WITH SNOW LEVELS
FALLING TO AROUND 5K FT MSL. KTVL AND KTRK WILL BOTH START AS
RAIN...BUT WILL TURNOVER TO SNOW BY THE LATE AFTERNOON/EARLY EVENING
TUESDAY. CONDITIONS WILL BE VFR-MVFR IN THE RAIN AND MVFR-IFR IN THE
SNOW. EXPECT WIDESPREAD MOUNTAIN OBSCURATION ALL DAY TUESDAY.

AM NOT EXPECTING MUCH IN THE WAY OF SPILLOVER INTO KRNO...BUT LIGHT
RAIN IS POSSIBLE THROUGHOUT THE DAY WITH A 50% CHANCE FOR PERIODS OF
MVFR CONDITIONS.

THE PRECIP WILL CLEAR OUT OF THE REGION BY WEDNESDAY MORNING. DF

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WIND ADVISORY FROM 7 AM TO 7 PM PST TUESDAY NVZ003-005.

     WINTER WEATHER ADVISORY FROM 7 AM TUESDAY TO 1 AM PST WEDNESDAY
     NVZ002.

     LAKE WIND ADVISORY FROM 7 AM TO 7 PM PST TUESDAY FOR PYRAMID
     LAKE IN NVZ004.

CA...WIND ADVISORY FROM 7 AM TO 7 PM PST TUESDAY CAZ070-071.

     WIND ADVISORY FROM 10 AM TO 7 PM PST TUESDAY CAZ073.

     WINTER WEATHER ADVISORY FROM 7 AM TUESDAY TO 1 AM PST WEDNESDAY
     CAZ072.

&&

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