Flash Flood Warning 53, NWS Las Vegas, NV

MOJAVE DESERT/SOUTHERN GREAT BASIN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
900 AM PDT THU JUL 29 1999

SYNOPSIS...SOUTHERLY WINDS ALOFT WILL CONTINUE TO PROVIDE A FLOW OF
MOIST AND UNSTABLE AIR TO THE MOJAVE DESERT AND PARTS OF SOUTH
CENTRAL NEVADA THROUGH FRIDAY. THIS WILL HELP FUEL THE DEVELOPMENT OF
SCATTERED THUNDERSTORMS EACH AFTERNOON AND EVENING. A DRIER AND MORE
STABLE FLOW OF AIR WILL PREVAIL OVER THE REST OF THE SOUTHERN GREAT
BASIN.

DISCUSSION...ETA AND MESO ETA THE WAY TO GO THIS MORNING AS THEY HAVE
BEST INITIALIZED AND DEPICTED MID-LEVEL CIRCULATION OVER SW AZ. MESO
ETA JUST A BIT FAST AND TOO FAR N WITH THIS FEATURE AT 15Z BUT MAKING
THAT ADJUSTMENT IT APPEARS TO BE DOING QUITE WELL. MODERATE LOW LEVEL
CONVERGENCE ON THE NORTHWEST SIDE OF THIS SYSTEM ALREADY PROVIDING A
FOCUS FOR SHOWERS AND A FEW THUNDERSTORMS ACROSS SAN BERNARDINO...
CLARK AND MOHAVE COUNTIES. TO SAY THE LEAST...ATMOSPHERE VERY MOIST
AND UNSTABLE WITH 12Z DRA SOUNDING AND LAPS ANALYSIS INDICATING CAPES
OF +1500 J/KG AND LIFTED INDICES OF -2 TO -5 ACROSS CLARK AND MOHAVE
COUNTIES. FORECAST PARAMETERS FROM THE MESO ETA AND LOCAL RAMS MODEL
INDICATE INCREASING CAPE (2000-2500 J/KG) AND LOW-LEVEL FORCING
THROUGH THE AFTERNOON FROM MOHAVE AND CLARK COUNTIES UP INTO LINCOLN
COUNTY. MISSING INGREDIENT IS HEATING FROM THE SUN BUT THAT MIGHT NOT
BE NECESSARY IF THE PREDICTED FORCING PANS OUT. COMPARED TO THE MAJOR
FLASH FLOOD EVENT EARLIER IN THE MONTH...THIS ONE APPEARS TO BE MUCH
LESS OF A THREAT AS PRECIPITABLE WATER VALUES ARE LOWER AND FORCING
IS WEAKER...BUT STILL ENOUGH TO WARRANT CONCERN.

WILL BE UPDATING ZONES TO ISSUE FLASH FLOOD WATCH UNTIL MIDNIGHT AND
ADJUST PRECIPITATION CHANCES AND TEMPERATURES A BIT. WATCH AND ZONES
OUT BY 10 AM PDT.

NEMETH

.LAS...A FLASH FLOOD WATCH HAS BEEN ISSUED. PLEASE REFER TO THE
LATEST FLASH FLOOD WATCH STATEMENT (RNOFFALAS) FOR DETAILS.

AZZ001>003-036-CAZ028-029-NVZ015>022-300700-

URGENT - IMMEDIATE BROADCAST REQUESTED
FLASH FLOOD WATCH
NATIONAL WEATHER SERVICE LAS VEGAS NV
930 AM PDT THU JUL 29 1999

...RETRANSMISSION OF WATCH FOR AREA STATE WARNING POINTS...

THE NATIONAL WEATHER SERVICE IN LAS VEGAS HAS ISSUED A FLASH FLOOD
WATCH EFFECTIVE UNTIL MIDNIGHT PDT/MST THURSDAY EVENING FOR PEOPLE
IN THE FOLLOWING COUNTIES:

IN SOUTHERN NEVADA
     CLARK...SOUTHERN LINCOLN AND EXTREME SOUTHEASTERN NYE

IN SOUTHEAST CALIFORNIA
     EASTERN SAN BERNARDINO

IN NORTHWEST ARIZONA
     MOHAVE

THUNDERSTORMS WITH LOCALLY HEAVY RAIN WILL LIKELY DEVELOP THIS
AFTERNOON AS AN UPPER LEVEL DISTURBANCE MOVES NORTH THROUGH WESTERN
ARIZONA AND INTERACTS WITH AN EXTREMELY MOIST AND UNSTABLE AIRMASS
OVER PARTS OF SOUTHERN NEVADA...SOUTHEAST CALIFORNIA...AND NORTHWEST
ARIZONA. STORMS ARE EXPECTED TO BE SLOW-MOVING AS A RESULT OF A
LIGHT WIND FLOW ALOFT. THIS WILL INCREASE THE CHANCE FOR FLASH
FLOODING BY ALLOWING SIGNIFICANT RAINFALL TO ACCUMULATE OVER A
RELATIVELY SMALL AREA. RAINFALL TOTALS IN THE 1.5 TO 3.0 INCH RANGE
CAN BE EXPECTED IN SOME LOCATIONS WITHIN THE WATCH AREA.

REMEMBER...A FLASH FLOOD WATCH MEANS THAT THERE IS A THREAT OF FLASH
FLOODING IN AND CLOSE TO THE WATCH AREA. THOSE HIKING OR CAMPING
SHOULD AVOID DRY STREAM BEDS AND WASHES AND STAY AWAY FROM NARROW
CANYONS WHERE FLOOD WATERS CAN BECOME KILLERS. FLASH FLOODS CAN OCCUR
MANY MILES FROM THE PARENT THUNDERSTORMS.

IF YOU ARE IN THE WATCH AREA...REVIEW SAFETY MEASURES AND BE
PREPARED TO MOVE TO HIGHER GROUND IN THE EVENT A FLASH FLOOD WARNING
IS ISSUED OR FLOODING IS OBSERVED.