Heavy Snow and High Wind in Nevada, February 23 to 24, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
400 PM PST SAT FEB 23 2008

.SHORT TERM...
A VERY TRICKY FORECAST IT IS TURNING OUT TO BE THIS AFTERNOON. WE
WERE EXPECTING SNOW LEVELS TO RISE TO NEAR 6000 FEET BEFORE FALLING
OFF LATE TONIGHT IN THE SIERRA AND ACROSS FAR WESTERN NEVADA.
HOWEVER...WE HAVE MADE A SIGNIFICANT ADJUSTMENT TO THE FORECAST
BASED ON THE LATEST OBSERVATIONAL INFORMATION FROM AROUND THE
REGION. LOOKING UPSTREAM AT THE 21Z SOUNDING FROM OAKLAND...WE WERE
SURPRISED TO SEE LITTLE ADDITIONAL WARMING BELOW 700 MB...MEANING
THAT STRONG WARM ADVECTION ALOFT IS STABILIZING THE LOWEST LAYERS
AND PREVENTING MIXING DOWN OF THE WARMER AIR (WHICH WOULD RAISE SNOW
LEVELS). HOWEVER...THE WARMER AIR IS TRYING TO MIX DOWN AS THE SOUTH
LAKE TAHOE OBSERVATION CURRENTLY HAS A WET BULB OF 0-1C...WHICH
WOULD THEORETICALLY PUT THEM JUST ABOVE THE SNOW/RAIN LINE. THE
KICKER IS THAT WHILE WARM ADVECTION IS TRYING TO RAISE THE SNOW
LEVELS...STRONG JET DYNAMICS HAVE BEGUN TO WORK ON THE ATMOSPHERE.
THIS WILL HAVE THE EFFECT OF COUNTERACTING THE WARMING...ESPECIALLY
BY 03-06Z. THEREFORE...WE NO LONGER EXPECT SNOW LEVELS TO RISE MUCH
ABOVE THE VALLEY FLOORS ACROSS FAR WESTERN NEVADA BEFORE FALLING
BACK DOWN BY LATE EVENING. THIS MAY LEAD TO A PERIOD OF RAIN/SNOW
MIX BELOW 5000 FEET FOR A COUPLE HOURS EARLY THIS EVENING.

OVERNIGHT...POWERFUL JET DYNAMICS WILL KEEP PRECIP GOING THROUGH
09Z-12Z FOR MUCH OF THE REGION...WITH PERIODS OF MODERATE TO HEAVY
SNOW OVER FAR WESTERN NEVADA AND IN THE SIERRA. SEE OUR UPGRADE TO A
HEAVY SNOW WARNING FOR THE RENO-CARSON CITY AREA FOR MORE DETAILS ON
AMOUNTS. SUNDAY...SNOW/SNOW AND RAIN SHOWERS IN THE BASIN
CONTINUE...ESPECIALLY IN THE SIERRA AND NORTH OF INTERSTATE 80 IN
THE BASIN. THE MAIN LOW WILL SWING THROUGH IN A MUCH WEAKENED
FASHION IN THE LATE AFTERNOON...FOR ANOTHER CONCENTRATED PERIOD OF
SHOWERS. THIS IS WHY THE SNOW ADVISORY/HEAVY SNOW WARNINGS IN THE
BASIN WERE CONTINUED UNTIL 00Z MONDAY. IT REMAINS TO BE SEEN IF THE
SNOW WILL BE HEAVY ENOUGH (REQUIRED THIS TIME OF YEAR IN THE
DAYTIME) TO CAUSE ROAD PROBLEMS OUTSIDE OF THE SIERRA.

MONDAY AND TUESDAY...AN UPPER RIDGE BUILDS IN FOR QUICK WARMING
ACROSS THE REGION WITH A STRENGTHENING SUN AND LITTLE COLD AIR TO
BUILD IN BEHIND TONIGHT AND SUNDAYS SYSTEM. SNYDER

.LONG TERM...WEDNESDAY THROUGH SATURDAY...
HIGH PRESSURE WILL BRING GENERALLY DRY WEATHER WITH NEAR OR ABOVE
NORMAL TEMPERATURES TO THE SIERRA AND WESTERN NV THROUGH THE PERIOD.
THE GFS SHOWS A WEAK SHORT WAVE MOVING THROUGH THE RIDGE WEDNESDAY
AFTERNOON AND EARLY WEDNESDAY NIGHT BRINGING INCREASED CLOUD COVER.
THE ECMWF HANDLES THE SHORT WAVE DIFFERENTLY BY PINCHING OFF A
CLOSED LOW AND TRACKING IT SOUTHEAST OFF THE CA COAST BY EARLY
THURSDAY. THE GFS PRODUCES SOME LIGHT PRECIPITATION IN THE SIERRA
AROUND TAHOE FOR LATE WED INTO EARLY WED NIGHT BUT THE EC KEEPS US
DRY. FOR NOW WILL BRING IN SOME LOW POPS BUT NO MENTION OF PCPN. A
STRONGER SYSTEM PUSHES INTO THE PACNW FRIDAY AFFECTING NORTHERN CA
AND THE SIERRA FROM TAHOE NORTH FRIDAY NIGHT OR SAT. THE GFS IS
CURRENTLY ABOUT 12 HOURS FASTER THAN THE EC WITH THE SYSTEM AND ALSO
FURTHER NORTH WITH THE CORE OF THE JET. RIGHT NOW IT LOOKS AS
THOUGH THIS SYSTEM WILL BRING PRECIPITATION TO THE SIERRA FROM TAHOE
NORTH INCLUDING THE VALLEYS OF NORTHEAST CA AND NORTHWEST NV. JAH
&&

.AVIATION...
SIERRA - HEAVY SNOW WILL CONTINUE IN THE SIERRA WITH LIFR CONDITIONS
THROUGH 12Z. THERE MAY BE A WINDOW OF DECREASE IN SNOWFALL INTENSITY
AROUND 12Z BEFORE REINTENSIFYING BY 16Z AS A SECOND WAVE OF ENERGY
AND MOISTURE PUSHES THROUGH. KTRK AND KTVL WILL SEE SNOW
ACCUMULATIONS OF AT LEAST A FOOT FROM 00Z-12Z SUNDAY WITH ADDITIONAL
SNOW DURING THE DAY SUNDAY.

WESTERN VALLEYS INCLUDING KLOL - RAIN WILL SPREAD ACROSS THE WESTERN
VALLEYS OF NEVADA AFTER 00Z SUNDAY. EXPECT SNOW TO CHANGE TO RAIN
FROM NORTH TO SOUTH BETWEEN 06Z-12Z WITH KLOL CHANGING TO SNOW
AROUND 09Z. MOST VALLEY LOCATIONS WILL PICK UP 1-3 INCHES OF SNOW
THROUGH 15Z SUNDAY WITH LOCALLY HIGHER AMOUNTS POSSIBLE. EXPECT
NUMEROUS CONVECTIVE SNOW SHOWERS AFTER 18Z SUNDAY.

KRNO - SNOW OCCURRING AT THE AIRPORT AS OF 22Z. THIS MAY CHANGE TO A
RAIN/SNOW MIX FOR A FEW HOURS 00Z-03Z BEFORE A PERIOD OF MODERATE TO
HEAVY SNOW SETS IN FROM AROUND 03Z - 09Z. SNOW WILL BEGIN TO
ACCUMULATE ON THE RUNWAYS AFTER 04Z WITH 3 TO 4 INCHES OF
ACCUMULATION. THERE WILL BE A RELATIVELY QUICK END TO THE SNOW BY
14Z. AFTER 20Z EXPECT NUMEROUS CONVECTIVE SNOW SHOWERS IN THE
VICINITY OF KRNO. JAH
&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER STORM WARNING UNTIL 10 PM PST SUNDAY FOR NVZ002.

     SNOW ADVISORY UNTIL 4 PM PST SUNDAY FOR NVZ005.

     HEAVY SNOW WARNING UNTIL 4 PM PST SUNDAY FOR NVZ003.

CA...WINTER STORM WARNING UNTIL 10 PM PST SUNDAY FOR CAZ071>073.

     SNOW ADVISORY UNTIL 4 PM PST SUNDAY FOR CAZ070.
&&

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