Heavy Snow in California, April 18 to 19, 2005

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
625 PM PDT MON APR 18 2005

.UPDATE...
COLD AND UNSTABLE TROUGH CONTINUES TO WORK SOUTHWARD INTO THE
GREAT BASIN THIS EVENING WITH IMPRESSIVE SHORTWAVE WORKING SOUTHWARD
ALONG WESTERN PERIPHERY TROUGH INTO WESTERN NEVADA AND THE EASTERN
SIERRA. STRONG UPPER LEVEL DIVERGENCE AHEAD OF THIS SHORTWAVE WAS
COMBINING WITH THE STEEPENING LAPSE RATES AND STRONG LOW LEVEL
CONVERGENCE(AS NOTED IN THE 01Z SURFACE ANALYSIS) TO ENHANCE  A
MESOSCALE BAND OF VERTICAL LIFT FROM THE NORTHERN SIERRA AROUND
TRUCKEE EASTWARD ALONG THE I-80 CORRIDOR. SPOTTER REPORTS INDICATE
DETERIORATING ROAD CONDITIONS IN THE FOOTHILLS NEAR VIRGINIA CITY
AND POOR VISIBILITY IN HEAVY SNOW ABOVE 5000 FEET. BAND WILL REMAIN
NEARLY STATIONARY UNTIL MID EVENING WHEN 700MB CYCLONIC AXIS IS
PROGGED TO HELP PUSH FOCUS OF ACTIVITY SOUTHWARD ALONG THE UPSLOPE
REGIONS OF THE EASTERN SIERRA. HEAVIEST PRECIPITATION WILL OCCUR
NEAR LOCATION OF CURRENT STATIONARY BAND WITH WIDESPREAD BUT LIGHTER
AMOUNTS FURTHER SOUTH ONCE BAND BEGINS TO PUSH SOUTHWARD. HOHMANN

.SHORT TERM...EARLIER DISCUSSION
UPPER LOW OVER THE GREAT BASIN WILL CONTINUE EAST THROUGH THE SHORT
TERM.  VORT MAX MOVING ACROSS THE CENTRAL SIERRA THIS AFTERNOON
KICKED OFF SCATTERED SHOWERS FROM THE TAHOE BASIN SOUTHEAST INTO
CHURCHILL COUNTY.  COLD AIR ALOFT WILL KEEP THE AIR MASS FAIRLY
UNSTABLE THROUGH TUESDAY NIGHT.  THE GFS PROGS LIFTED INDICES OF
LESS THAN ZERO OVER THE TAHOE BASIN TUESDAY AFTERNOON.  THE ETA IS
JUST AS UNSTABLE BUT HAS ZERO LIFTED INDICES FARTHER SOUTH OVER
MINERAL COUNTY.

THE COMBINATION OF THE VORT MAX MOVING THROUGH TONIGHT...AND THE
COLD AIR ALOFT...WILL KEEP SCATTERED SHOWERS OVER THE KREV CWFA.
ANY ACCUMULATIONS WILL BE LIGHT WITH A COUPLE OF INCHES POSSIBLE IN
THE TAHOE BASIN AND UP TO AN INCH IN THE WESTERN FOOTHILLS OF THE
RENO AREA NORTH TO LASSEN COUNTY.  THE SYSTEM MOVES TO THE EASTERN
GREAT BASIN ON WEDNESDAY.  NORTHERLY FLOW WILL KEEP TEMPERATURES
SLIGHTLY BELOW NORMAL ON WEDNESDAY.  THE UPPER LOW STARTS TO FILL
AND MOVES NORTH TO IDAHO ON THURSDAY.  A FLAT RIDGE WILL BUILD INTO
THE SOUTHWESTERN CONUS WITH ZONAL FLOW OVER NORTHERN CALIFORNIA AND
NEVADA. TEMPERATURES WILL REBOUND TO NEAR NORMAL LEVELS BY THURSDAY.
OHARA

.LONG TERM...FRIDAY THROUGH MONDAY...
STILL LOOKING RATHER BENIGN UNTIL THE LOW PROGGED TO BE OVER CENTRAL
NEVADA SHIFTS NORTH THEN WEST UNTIL BLENDING WITH THE LOW
APPROACHING FROM THE SW OFF THE PACIFIC. THE GFS AS WELL AS THE EURO
ARE STARTING TO AGREE THAT THE NEW COMBINED LOW SETS UP OFF SHORE
THUS PUTTING THE CWA INTO A MORE FAVORABLE  LEFT EXIT REGION OF THE
JET. CANT RULE OUT THE POSSIBILITY OF ACTIVE CONVECTION INCLUDING
THE POSSIBILITY OF AN ISOLATED THUNDERSTORM OR TWO OVER THE SIERRA
ON SATURDAY AFTERNOON THEN SPREADING ACROSS THE ENTIRE CWA FOR
SUNDAY AFTERNOON. SHOWERS LOOK TO PERSIST INTO NEXT WEEK AS THE
OFFSHORE LOW SLOWLY PUSHES NORTHWEST AS PER THE GFS.

CLOUD COVER APPEARS TO BE ON THE INCREASE WITH THE BLENDING OF THE
TWO SYSTEMS THUS HAVE MADE SIGNIFICANT INCREASES TO SKY COVER GRIDS
AND HAVE TRENDED TEMPERATURES DOWN SLIGHTLY AS DAYTIME HEATING WILL
BECOME LIMITED. JBONK
&&

.REV WATCHES/WARNINGS/ADVISORIES...
.NV...SNOW ADVISORY NVZ002-003 UNTIL 1AM PDT TUESDAY.
.CA...SNOW ADVISORY CAZ071-072 UNTIL 1AM PDT TUESDAY.
&&