Lake Wind Advisory 33, NWS Reno, NV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
400 AM PST WED DEC 19 2007

.SHORT TERM...
THE REGION IS CURRENTLY IN A LULL BETWEEN TWO STORM SYSTEMS WITH ONE
EXITING OVER SRN NV AND THE NEXT DEVELOPING OVER THE ERN PACIFIC
AROUND 150W. THERE IS ALSO A WEAK SHORTWAVE CURRENTLY MOVING INTO
THE PACNW WHICH SHOWS UP WELL ON SATELLITE IMAGERY. THIS SHORTWAVE
HAS STRONG WAA SOUTH OF IT WHICH IS SPREADING A GOOD SLUG OF
MOISTURE OVER NRN CA/NV THIS MORNING. THE BEST UPPER FORCING STAYS
WELL NORTH OF THE CWA SO LITTLE IN THE WAY OF PRECIP IS EXPECTED...
HOWEVER PERIODS OF LIGHT SNOW WILL OCCUR ALL DAY OVER FAR NRN LASSEN
COUNTY AND IN THE SURPRISE VALLEY.

THE BIGGER STORY IS THE NEXT PACIFIC SYSTEM WHICH IS ON TRACK TO
MOVE INTO THE REGION THIS AFT/EVE. OVERRUNNING PRECIP STARTS TO
INCREASE OVER THE NRN SIERRA THIS AFTERNOON AND SPREADS SOUTH TO
AROUND THE I80 CORRIDOR JUST AFTER SUNSET. THE ORIENTATION OF THE
UPPER JET AND THE WAY THIS SYSTEM COMES ONSHORE ARE NOT CONDUCIVE TO
SPLITTING OR SHEARING THIS SYSTEM APART...SO CONFIDENCE IS HIGH ON
THIS STORM. ONE THING THAT IS A LITTLE UNCERTAIN IS THE MOISTURE
AVAILABLE TO THE STORM. TPW VALUES ARE SLIGHTLY HIGHER THAN THE
PREVIOUS STORM...HOWEVER THE MOISTURE TAP GETS CUT OFF RATHER
QUICKLY AND THERE IS SOME UNCERTAINTY ON THE AMOUNT OF POST-FRONTAL
PRECIP. THE COLD AIR PORTION OF THIS STORM IS MUCH COLDER THAN THE
LAST SO SNOW RATIOS WILL BE QUITE HIGH WHICH WILL ADD UP TO HIGHER
SNOW AMOUNTS. TOTAL QPF FOR THIS SYSTEM IS EXPECTED TO BE AROUND 1.5
INCHES ALONG THE SIERRA CREST FROM TAHOE NORTH WITH AROUND AN INCH
TO THE SOUTH. WITH THE HIGH SNOW RATIOS THIS SHOULD ADD UP TO OVER 2
FEET ALONG THE CREST QUICKLY TAPERING OFF TO THE EAST. WINDS WILL BE
VERY STRONG DURING THIS STORM AS H7 SPEEDS REACH 65 KTS COUPLED WITH
GOOD UPPER SUPPORT FROM THE JET MAX ALOFT. COULD EASILY SEE GUSTS TO
100 MPH OVER THE SIERRA RIDGES WITH THE STRONGEST WINDS OCCURRING
THURSDAY MORNING AS THE FRONT PASSES. WILL UPGRADE THE WINTER STORM
WATCHES TO WINTER STORM WARNINGS FOR THE SIERRA ZONES.

FOR AREAS IN THE LEE OF THE SIERRA...AN INVERSION FORMS AROUND RIDGE
LEVEL AS THE INITIAL BAND OF PRECIP BANKS UP AGAINST THE WRN SLOPES
OF THE SIERRA WHICH WILL ONCE AGAIN DEVELOP THE RAIN SHADOW. THIS
CRITICAL LEVEL WILL HELP TO DUCT THE HIGH WINDS ALOFT DOWN TO THE
SURFACE. LOCAL WIND ALGORITHM SHOWS HIGH WIND CRITERIA BEING MET
WITH MODELS INDICATING SPEEDS AROUND 30 KTS WITH GUSTS TO 55 KTS.
WILL ISSUE A HIGH WIND WATCH TO COVER THIS THREAT AND LET THE DAY
SHIFT LOOK AT 12Z MODEL RUNS TO MAKE FINAL DECISION. A STRONG COLD
FRONT MOVES INTO THE NRN ZONES EARLY THURSDAY MORNING AND INTO THE
RENO AREA SOON AFTER SUNRISE. THE STRONGEST WINDS WILL OCCUR AROUND
THIS TIME AND RAPIDLY DECREASE BEHIND IT. THIS WILL ALSO BE WHEN
SPILLOVER INTO THE LEE OF THE SIERRA OCCURS WITH SNOW LEVELS QUICKLY
DROPPING TO ALL VALLEY FLOORS. AS MENTIONED PREVIOUSLY...ITS STILL
TOUGH TO SAY HOW MUCH POST-FRONTAL SNOWFALL OCCURS. MAY NEED TO
ISSUE A SNOW ADVISORY FOR SOME WRN NEVADA ZONES AS THIS BECOMES MORE
CLEAR.

THE STORM EXITS TO THE EAST THURSDAY NIGHT WITH HIGH PRESSURE
BUILDING IN BRINGING RAPIDLY CLEARING BLUEBIRD SKIES BY FRIDAY
MORNING. SURFACE HIGH PRESSURE STRENGTHENS OVER THE GREAT BASIN
CAUSING NELY POST-FRONTAL WINDS TO BE GUSTY AT TIMES OVER THE
HIGHEST SIERRA RIDGES. AT THIS TIME IT APPEARS GUSTS SHOULD REMAIN
BELOW 50 MPH AND GUSTY WINDS ON LAKE TAHOE ARE NOT ANTICIPATED.
FRIDAY NIGHT WILL BE QUITE CHILLY WITH CLEAR SKIES...A FRESH LAYER
OF SNOW...AND A COLD POST-FRONTAL AIRMASS. JORDAN

.LONG TERM...SATURDAY THROUGH CHRISTMAS DAY...
SHORTWAVE RIDGE STILL PROGGED TO BE SHIFTING EAST OF AREA SATURDAY
AS UPSTREAM SHORTWAVE MOVES INTO THE PACNW IN FAST PROGRESSIVE FLOW.
THERE IS QUITE A BIT OF UNCERTAINTY IN DETAIL DURING THE PERIOD
GIVEN THE PROGRESSIVE NATURE OF SYSTEMS ENTERING THE PACNW. THERE
SEEMS TO BE A GENERAL SIGNAL AMONG DETERMINISTIC AND ENSEMBLE RUNS
THAT A WEAK SHORTWAVE WILL BRUSH THE AREA SATURDAY NIGHT FOLLOWED BY
ONE SLIGHTLY STRONGER AND FURTHER SOUTH SOMETIME EARLY NEXT WEEK.
NEITHER SYSTEM APPEARS TO HAVE MUCH PUNCH AND WOULD ONLY PRODUCE
LIGHT QPF BASED ON CURRENT PROJECTIONS. THE MAIN EMPHASIS WILL BE ON
A CONTINUATION OF VARIABLE CLOUDY CONDITIONS AND SOME CHANCE OF
PRECIPITATION WITH THE BEST OPPORTUNITY BEING NORTHEAST CALIFORNIA.
TEMPERATURES WILL BEGIN TO WARM AT THE MOUNTAIN TOPS SATURDAY
ALTHOUGH VALLEYS WILL CONTINUE TO BE QUITE COLD AT NIGHT. READINGS
EARLY NEXT WEEK WILL RETURN TO NEAR NORMAL MOST AREAS WITH UPPER 30S
AND 40S MOST VALLEY LOCATIONS. HOHMANN
&&

.AVIATION...
SKIES CLEARED OVERNIGHT AND ALLOWED TEMPERATURES TO FALL CLOSE TO
DEWPOINTS IN THE SIERRA VALLEYS. WHILE RIDGE LINE WINDS CONTINUE TO
PRODUCE SOME MIXING...THE INVERSIONS MAY BE SUFFICIENT TO PRODUCE
PATCHY GROUND FOG AROUND DAYBREAK AND FOR SEVERAL HOURS AFTERWARDS
AT KTRK/KTVL. ANY FOG WILL BE SHALLOW AND BURN OFF BY 16Z. NEXT
STORM TO BRING AN INCREASE IN WIND THIS EVENING INTO THURSDAY
MORNING. WIDESPREAD WIND GUSTS WILL AFFECT THE KTVL/KTRK TAF SITES
FOR SEVERAL HOURS THIS EVENING (22Z-04Z) PRIOR TO HEAVY SNOW AND
LIFR CONDITIONS RESUMING AND CONTINUING OVERNIGHT. AT KRNO...WINDS
WILL GUST 35-40KT WITH LOCAL GUSTS TO 50-55KT IN THE VCNTY OF THE
AIRPORT...MAINLY AFTER 04Z AND CONTINUING INTO THURSDAY MORNING.
HOHMANN
&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...HIGH WIND WATCH FROM THIS EVENING THROUGH THURSDAY MORNING FOR
     NVZ003-005.

     LAKE WIND ADVISORY FROM NOON TODAY TO 8 PM PST THIS EVENING FOR
     NVZ002.

     WINTER STORM WARNING FROM 8 PM THIS EVENING TO 4 PM PST THURSDAY
     FOR NVZ002.

CA...WINTER STORM WARNING FROM 4 PM THIS AFTERNOON TO 4 PM PST
     THURSDAY FOR CAZ071.

     HIGH WIND WATCH FROM THIS EVENING THROUGH THURSDAY MORNING FOR
     CAZ070.

     WINTER STORM WARNING FROM 8 PM THIS EVENING TO 8 PM PST THURSDAY
     FOR CAZ073.

     LAKE WIND ADVISORY FROM NOON TODAY TO 8 PM PST THIS EVENING FOR
     CAZ072.

     WINTER STORM WARNING FROM 8 PM THIS EVENING TO 4 PM PST THURSDAY
     FOR CAZ072.

&&

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