Severe Thunderstorm Warning 9, NWS Las Vegas, NV

MOJAVE DESERT/SOUTHERN GREAT BASIN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
310 PM PDT TUE JUL 21 1998

SYNOPSIS...AN UPPER LEVEL HIGH PRESSURE SYSTEM WILL REMAIN NEAR THE
FOUR CORNERS AREA THROUGH MUCH OF THE WEEK. THIS WILL CONTINUE TO
BRING A FLOW OF MONSOONAL MOISTURE INTO THE REGION...HELPING TO FUEL
SCATTERED AFTERNOON AND EVENING THUNDERSTORMS.

DISCUSSION...PLENTY OF MOISTURE TODAY WITH 850 DEW POINT AXIS FROM
SRN AZ INTO SOUTH CENTRAL NV. SURFACE DEW POINTS BEGINNING TO MIX OUT
SOMEWHAT WITH 60 TO 65 DEGREES F REMAINING ACROSS EXTREME SRN NV AND
IN EXCESS OF 70 DEGREES STILL POOLED OVER THE SE CA DESERTS AND
COLORADO RIVER AS FAR N AS BLH AND EED.  THUNDERSTORMS HAVE INITIATED
MAINLY OVER THE MOUNTAINS IN NV AND NW AZ AND HAVE NOT BEEN IN ANY
HURRY TO MOVE OFF DUE TO WEAK MID AND UPPER LEVEL FLOW.  HOWEVER...AS
STORMS CONTINUE TO GROW...ANTICYCLONIC FLOW AROUND FOUR CORNERS HIGH
WILL SLOWLY PUSH STORMS OFF MOUNTAINS AND INTO VALLEYS.  OUTFLOW
BOUNDARY INTERACTION WILL THEN CONTRIBUTE TO STORM FORMATION WITH
THUNDERSTORMS CONTINUING INTO THE LATE EVENING.

SYNOPTIC PATTERN CHANGES VERY LITTLE THROUGH THURSDAY WITH UPPER HIGH
REMAINING NEAR FOUR CORNERS REGION PROVIDING S-SELY FLOW. LOW AND MID
LEVEL MOISTURE/THETA-E AXIS REMAINS CLOSE TO A TPH TO YUM LINE. WITH
WEAK FLOW OF PLENTY OF MOISTURE...MAIN THREAT WILL BE FLASH FLOODING
WITH HIGHER POPS OF NGM MOS PREFERRED.  VERY DIFFICULT TO FIND ANY
SYNOPTIC SCALE TRIGGERING MECHANISMS BUT WILL CLOSELY WATCH MID/UPPER
LEVEL DISTURBANCE NOW OFF BAJA COAST NEAR THE SPUR. NGM THE ONLY
MODEL THAT SEEMS TO HAVE IDENTIFIED IT AND BRINGS IT N INTO SRN NV
LATE WED NGT/THU.  NOT READY TO BUY INTO THIS JUST YET BUT WOULD SEEM
REASONABLE. OTHERWISE...MESOSCALE TRIGGERING MECHANISMS WILL DOMINATE
WITH HEAVY RELIANCE ON SATELLITE TO HELP IDENTIFY AND TRACK THESE
FEATURES.  RIDGE REMAINS IN PLACE INTO THE EXTENDED AND SLOWLY
WEAKENS.  ANY DRYpING WILL ALSO BE SLOW SO CONTINUATION OF STANDARD
MONSOON FORECAST THE BEST WAY TO GO. LAS 3343. NEMETH

A FLASH FLOOD WATCH HAS BEEN ISSUED. PLEASE REFER TO THE LATEST FLASH
FLOOD WATCH BULLETIN FOR DETAILS.