Strong Wind and Winter Weather in Nevada, April 7 to 8, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
547 PM PDT TUE APR 7 2009

.UPDATE...
BAND OF MODERATE TO HEAVY PCPN IS PIVOTING INTO THE LAKE TAHOE
BASIN ATTM. KTVL HAS SWITCHED TO SNOW WITH THE TEMP NOW DOWN TO 37
DEGREES. THIS BAND IS THE AHEAD OF THE MAIN UPPER LOW MOVING
TOWARD THE COAST. JET STREAK ROUNDING THE BASE OF THE UPPER LOW IS
INTERACTING WITH MSTR OVER THE CENTRAL VALLEY OF CA AS WELL AND
PRODUCING CONVECTION THAT IS MOVING TOWARD THE MONO COUNTY AREA AS
WELL. 18 UTC NAM AND GFS BOTH SHOWED AN INCREASE IN QPF FROM TAHOE
SOUTH TONIGHT IN LINE WITH CURRENT EVENTS. WITH TEMPERATURES
RAPIDLY DROPPING AT THE ONSET OF THE PCPN DUE TO WET BULB EFFECT
EXPECT SNOW LEVELS FROM TAHOE SOUTH TO FALL QUICKLY THIS EVENING
AND ACCUMULATIONS TO START. WHILE ROADS WILL BE MAINLY WET EARLY
ON ACCUMULATIONS ON GRASSY SURFACES WILL START EARLY THIS EVENING.
ACCUMULATIONS ON ROADS WILL START LATER THIS EVENING. WITH BURSTS
OF MODERATE TO SNOW POSSIBLE THINK ACCUMULATIONS COULD BE JUST A
BIT MORE THAN ORIGINALLY FORECAST. WINDS WILL ALSO CONTINUE TO
GUSTS AND WILL HELP REDUCE VSBYS THIS EVENING OVER THE SIERRA.
WILL ISSUE A WINTER WEATHER ADVISORY MAINLY FOR SNOW BUT WILL
MENTION GUSTY WINDS AS WELL. MLF

&&

.PREVIOUS DISCUSSION... /ISSUED 300 PM PDT TUE APR 7 2009/

SHORT TERM...
UPPER LOW OFF THE CALIFORNIA COAST BEGINNING TO MAKE PROGRESS EAST
AS SYSTEM UPSTREAM OVER THE GULF OF ALASKA IS FINALLY CLOSE ENOUGH
TO GIVE IT A NUDGE. UPPER LOW IS ON TRACK TO MOVE ACROSS THE AREA
TONIGHT AND THEN EAST OF AREA ON WEDNESDAY WITH NO SIGNIFICANT
CHANGES FROM THINKING PREVIOUS TO THIS PACKAGE. TEMPERATURES WERE
ALREADY BEGINNING TO COOL ALOFT AS NOTED BY THE CONVECTIVE NATURE OF
THE CLOUDS OVER CENTRAL CALIFORNIA/SIERRA. STRONG THERMAL GRADIENT
WILL CONTINUE TO SET UP ALONG THE SIERRA THIS AFTERNOON AND THEN
PUSH OFF TO THE EAST ACROSS WESTERN NEVADA AS UPPER LOW AND
ASSOCIATED JET APPROACH. PRECIPITATION IS EXPECTED TO INCREASE ALONG
THE SIERRA INTO THIS EVENING AS LIFT/INSTABILITY INCREASE IN LEFT
FRONT QUADRANT OF JET. THERE WILL BE A BRIEF BUT LOCALLY HEAVY
PERIOD OF SNOWFALL FOR THE HIGH SIERRA ABOVE 8000 FEET WHERE 6 TO 12
INCHES WILL BE POSSIBLE. LESSER AMOUNTS ARE ANTICIPATED ELSEWHERE IN
MONO/ALPINE COUNTIES ALTHOUGH SOME INCONVENIENCE IS POSSIBLE FOR
TRAVELERS ALONG THE HIGHWAY 395 CORRIDOR FROM WALKER TO MAMMOTH
LAKES AS SEVERAL INCHES OF SNOW ARE EXPECTED.

FRONT WILL TRANSLATE QUICKLY EASTWARD INTO SURFACE THERMAL TROUGH
OVER THE BASIN AND RANGE WHICH WILL GREATLY LIMIT SHOWERS FROM RENO
SOUTHEAST TO HAWTHORNE. FOCUS WILL SHIFT NORTH AND EAST ALONG THIS
BOUNDARY AND DEFORMATION AXIS OVERNIGHT. MODELS HAVE BEEN PERSISTENT
IN DEVELOPING BAND OF SHOWERS FROM NORTHEAST CALIFORNIA ACROSS
NORTHERN WASHOE TO NEAR AND EAST OF KLOL/KFAL AND THEN PIVOTING IT
NORTH WEDNESDAY MORNING. ISOLATED THUNDER WAS KEPT THIS EVENING IN
THESE AREAS ALTHOUGH LACK OF MOISTURE INITIALLY DURING THE EVENING
MAY BE A LIMITING FACTOR. CONFIDENCE IS HIGHER IN SHOWER BAND AND
THUS POPS/QPF WERE INCREASED CONSIDERABLY LATE THIS EVENING INTO
EARLY WEDNESDAY. SNOW LEVELS AND WARM TEMPERATURES WILL LIMIT
SNOWFALL ACCUMULATIONS OVER THE BASIN AND RANGE. IN DEFORMATION AXIS
ACROSS NORTHEAST CALIFORNIA/NORTHWEST NEVADA...CONDITIONS WILL BE
MORE FAVORABLE FOR ACCUMULATING SNOW IN TROWEL FEATURE TO NORTHWEST
OF UPPER LOW. THE COLDER GFS WAS FAVORED WITH NEAR FREEZING WET BULB
TEMPERATURES AT THE SURFACE AND ISOTHERMAL LAYER ABOVE. SOME OF THE
QPF MEMBERS SUGGEST THERE COULD BE HEAVY SNOW ACCUMULATIONS IN A
NARROW BAND. DUE TO UNCERTAINTY IN EXACT POSITION OF HEAVIEST BANDS
AND THE OUTSIDE CHANCE THAT THE WARMER NAM COULD VERIFY...AMOUNTS
WERE KEPT IN ADVISORY CRITERIA WITH 2-4 INCHES MOST LIKELY. IN ANY
CASE IT LOOKS TO BE A WET AND HEAVY SNOW. WINDS WILL GENERALLY NOT
BE A PROBLEM EXCEPT FOR BRIEFLY THROUGH EARLY EVENING WHEN GUSTS
WILL APPROACH OR EXCEED 30 MPH.

SHOWERS WILL BEGIN TO DIMINISH WEDNESDAY AFTERNOON AS UPPER LOW
OPENS AND LIFTS NORTHEAST. A BREAK WEDNESDAY NIGHT AND THURSDAY WILL
BE FOLLOWED BY THE NEXT SYSTEM THURSDAY NIGHT AND FRIDAY WHICH IS
PROGGED TO TRACK SOUTHWARD ALONG THE WEST COAST. THAT SYSTEM IS
STILL FORECAST TO SPLIT WITH MUCH OF THE ENERGY DIVING SOUTHWARD
INTO BAJA. THE GFS HAS TRENDED BACK EASTWARD AND IS ALIGNED WELL
WITH THE ECMWF AND ALSO HAS DECENT ENSEMBLE SUPPORT. WHILE MUCH OF
THE JET ENERGY WILL REMAIN WEST AND SOUTH OF OUR AREA...DEEP
MOISTURE UNDER DEFORMATION AND EMBEDDED VORT MAXIMA SHOULD BE
SUFFICIENT TO BRING ANOTHER ROUND OF SHOWERS. CONFIDENCE HAS ALLOWED
FOR POPS TO BE INCREASED THURSDAY NIGHT INTO FRIDAY. SNOW LEVELS
SHOULD STAY JUST ABOVE THE LOWER VALLEY FLOORS ALTHOUGH SOME
FLUCTUATION IS EXPECTED. TEMPERATURES WILL BE COOL THE REST OF THE
WEEK WITH DAYTIME READINGS IN THE 40S AND 50S COMMON. HOHMANN

LONG TERM...SATURDAY THROUGH TUESDAY...
NUDGED UP POPS MONDAY NIGHT AND TUESDAY...OTHERWISE ONLY MINOR
CHANGES TO EXTENDED GRIDS.

RESIDUAL MOISTURE IN WEST TO NORTHWEST FLOW MAY ALLOW FOR A FEW
SHOWERS EARLY SATURDAY...ALTHOUGH THEY LOOK QUITE LIGHT. SATURDAY
NIGHT INTO MONDAY THE REGION GETS INTO A SHORT WAVE RIDGE BEFORE THE
ECMWF BRINGS IN A SPLITTING TROUGH MONDAY NIGHT AND TUESDAY.
MEANWHILE...THE GFS BRINGS ENERGY INTO THE PACIFIC NORTHWEST AND
FLATTENS THE RIDGE AS EARLY AS SUNDAY NIGHT. IT ALSO BRINGS IN SOME
SHOWERS TO THE SIERRA NEAR AND NORTH OF LAKE TAHOE AND ACROSS FAR
NORTHERN NEVADA. THE 12Z NAEFS SHOWS ALL PRECIP POTENTIAL FOR
NORTHWEST CALIFORNIA AND INTO OREGON SUNDAY NIGHT AND MONDAY...MORE
IN LINE WITH THE ECMWF. WITH SOME DISCREPANCY BUT MORE CONFIDENCE IN
THE ECMWF/NAEFS...I LEFT THE GHOST POPS THAT WERE PREVIOUSLY ENTERED
INTO THE GRIDS.

AS FAR AS PRECIP MENTION...I WILL SIDE WITH THE ECMWF CONCEPT AND
HOLD OFF PRECIP UNTIL MONDAY NIGHT AND TUESDAY AS THE SPLITTING
ENERGY IMPINGES ON THE REGION. I DID UP POPS FOR THAT TIME PERIOD
(MONDAY NIGHT NORTH AND THEN TUESDAY ALL OVER THE CWA) GIVEN THAT
THE ECMWF AND GFS RE-CONVERGE ON THE CONCEPT OF A TROUGH OVERHEAD.
THE DETERMINISTIC GFS AND EC ARE BACKED UP BY THE 12Z NAEFS...WHICH
SHOWS A -1.5 STANDARD DEVIATION IN THE 500 MB HEIGHT FIELD OVERHEAD
MONDAY NIGHT AND TUESDAY. THAT MUCH OF A DEVIATION INDICATES THAT
THE NAEFS HAS GOOD ENSEMBLE MEMBER SUPPORT FOR A TROUGH...WHICH
SUPPORTS ABOVE CLIMATOLOGICAL POPS FOR THE CWA. SNYDER

AVIATION...
FOR KRNO...NO CONCERNS WITH A FEW QUICK -SHRA OR SPRINKLES PSBL
CIRCA 04Z-08Z.

FOR KLOL...GUSTY SOUTH WINDS WILL CREATE BLDU UNTIL ARND 06Z...THEN
BLDU ENDING AS PREVAILING -RA (POSSIBLY REDUCING VSBYS TO 3-5SM IN
BRIEF RA) DEVELOPS TIL 12Z-15Z WEDNESDAY.

FOR KTVL/KTRK...VSBYS AND CIGS TO FALL RAPIDLY ONCE -SHRA OR -SHRASN
TURNS TO -SHSN CIRCA 04Z-06Z. WDSPRD -SHSN/SHSN TO CONTINUE FROM
06Z-CIRCA 15Z WEDNESDAY THEN DECREASE TO SCT -SHSN. KTVL DROP TO
PREVAILING CONDS BELOW MINIMUMS DURING THE 04/06Z TO 15Z PERIOD...
WITH KTRK DROPPING OCCASIONALLY TO BELOW INSTRUMENT APPROACH MINS AT
TIMES IN HEAVIER SHSN. SNYDER

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 11 AM PDT
     WEDNESDAY FOR NVZ005.

     WINTER WEATHER ADVISORY UNTIL 11 AM PDT WEDNESDAY FOR NVZ002.

     LAKE WIND ADVISORY UNTIL 8 PM PDT THIS EVENING FOR NVZ004.

CA...WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 11 AM PDT
     WEDNESDAY FOR CAZ070-071.

     WINTER WEATHER ADVISORY UNTIL 11 AM PDT WEDNESDAY FOR CAZ072-073.

&&

HTTP://WEATHER.GOV/RENO