Severe Thunderstorm Warning 15, NWS Las Vegas, NV

MOJAVE DESERT/SOUTHERN GREAT BASIN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
242 PM PDT WED AUG 30 2000

SYNOPSIS...A VERY MOIST AIRMASS REMAINS IN PLACE FOR THE THREAT OF
HEAVY RAIN AND FLASH FLOODING TONIGHT ACROSS MUCH OF THE SOUTHERN
GREAT BASIN AND MOJAVE DESERT. THE ATMOSPHERE WILL BEGIN TO
GRADUALLY DRY THROUGH FRIDAY...BUT THE THREAT OF THUNDERSTORMS WILL
REMAIN OVER MUCH OF THE REGION THROUGH THURSDAY NIGHT. ONLY HIGHER
ELEVATIONS WILL REMAIN AT RISK ON FRIDAY AS A LOW PRESSURE SYSTEM
FINALLY USHERS DRY AIR INTO THE REGION.

DISCUSSION...CONVECTION HAS BEEN SLOW TO FIRE DUE TO THE EXTENSIVE
CLOUD SHIELD OVER THE REGION. THESE CLOUDS MAY COMPLETELY
ELIMINATE THE RISK OF WIDESPREAD HEAVY RAIN AND FLASH FLOODING THIS
AFTERNOON AND EVENING. HOWEVER...I EXPECT A FEW MORE DEGREES OF
WARMING TO CAUSE AN INCREASE IN CONVECTION THIS AFTERNOON AND
EVENING. HOWEVER...THE SWING SHIFT WILL NEED TO MONITOR CLOSELY IN
ORDER TO DETERMINE WHETHER OR NOT TO CANCEL THE WATCH. FOR
NOW...WILL KEEP IT IN EFFECT UNTIL 2100 LST.

OVER THE SOUTHERN CWA...LATEST SOUNDER PRECIPITABLE WATER DATA
CONTINUES TO VERIFY THAT DRYING IS STARTING TO WORK ITS WAY INTO
SOUTHEAST CALIFORNIA. HOWEVER...DEW POINTS REMAIN QUITE HIGH SO MOST
OF THIS DRYING IS PROBABLY IN THE MID LEVELS OF THE ATMOSPHERE...AS
PREDICTED BY THE MODELS. MODELS...ESPECIALLY THE ETA WHICH HAD THE
BEST INITIALIZATION THIS MORNING...SUGGEST AN INCREASE IN LOW LEVEL
MOISTURE OVERNIGHT FROM THE SOUTHEAST...KEEPING THE AIRMASS PRIMED
FOR FURTHER DEVELOPMENT OF STORMS OVERNIGHT AND THROUGH THURSDAY
NIGHT.

THE MID LEVEL DRYING SHOULD ALSO CONTINUE UNABATED. HOWEVER...A
MORE FAVORABLE SHEAR PROFILE BECOMES ESTABLISHED AS THE WEAK OFFSHORE
LOW MOVES CLOSER TO THE COAST AND A JET STREAK ALOFT PROVIDES ADDED
LIFT. THIS WILL INCREASE THE CHANCES FOR SEVERE WEATHER ON
THURSDAY...WHILE AT THE SAME TIME DECREASING THE AREAL COVERAGE OF
STORMS THAT DO DEVELOP. BY FRIDAY...MOST OF THE CWA SHOULD DRY OUT
IN EARNEST WITH A SOLID LOW LEVEL SOUTHWEST FLOW IN PLACE. THE ONLY
LOCATIONS AT RISK FOR CONVECTION AT THIS TIME WILL BE THE HIGHER
TERRAIN OF CLARK...NYE AND MOHAVE COUNTIES. I DID NOT COMPLETELY DRY
OUT THE REGION AS DICTATED BY THE NGM/AVN BECAUSE THEY APPEARED TO
BE DOING SO TOO QUICKLY. THUS...I FAVORED THE SLOWER TIMING OF THE
ETA.

OVER THE NORTHERN CWA...DEFORMATION AXIS CURRENTLY OVER THE REGION
WILL SHIFT SLIGHTLY NORTHWARD BY TOMORROW...BUT WILL STILL PROVIDE
UPPER SUPPORT FOR STORMS THROUGH THURSDAY NIGHT. THUS...THIS REMAINS
THE FAVORED AREA FOR PRECIPITATION THROUGH THE SHORT-TERM. DRYING
STARTS TO WORK ITS WAY INTO THE REGION BY FRIDAY...BUT ENOUGH
MOISTURE WILL REMAIN FOR STORMS...ESPECIALLY THE HIGHER TERRAIN.

DURING THE EXTENDED PERIOD...OFFSHORE LOW PHASES WITH A NORTHERN TIER
UPPER TROUGH AT THE END OF THE SHORT-TERM...AND THE ENTIRE SYSTEM
SWINGS THROUGH THE WESTERN STATES...PROVIDING WINDY CONDITIONS...DRY
WEATHER AND MODERATING TEMPERATURES. JAH

.LAS...A FLASH FLOOD WATCH IS IN EFFECT FOR ALL OF SOUTHERN NEVADA
NORTHWEST ARIZONA AND MUCH OF EASTERN CWALIFORNIA. PLEASE REFER TO
THE LATEST RNOFFALAS AND RNOFLSLAS STATEMENTS FOR DETAILS.