Flash Flood Warning 38, NWS Las Vegas, NV

MOJAVE DESERT/SOUTHERN GREAT BASIN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
925 AM PDT TUE SEP 8 1998

SYNOPSIS...A LARGE TROUGH OF LOW PRESSURE WILL APPROACH THE WEST
COAST TUESDAY...THEN SLOWLY MOVE ACROSS THE GREAT BASIN WEDNESDAY.
AHEAD OF THIS SYSTEM....A MOIST SOUTHERLY FLOW OF AIR WILL REMAIN
ACROSS THE REGION RESULTING IN A CONTINUED THREAT OF AFTERNOON AND
EVENING THUNDERSTORMS.

DISCUSSION...UPPER TROUGH (ABOVE 400 MB) CONTINUES TO ELONGATE/WEAKEN
AND PUSH E WITH AXIS ALONG THE NV/UT BORDER.  ANY UPPER DIVERGENCE
FROM THIS SYSTEM NOW WELL TO THE E. ANOTHER WEAK VORT LOBE IS MOVING
NWD FROM SRN AZ HELPING FIRE STORMS ACROSS THE CENTRAL PART OF THAT
STATE...BUT SHOULD DRIFT N-NE AHEAD OF UPPER TROUGH AND MAY NOT BE A
FACTOR FOR NW AZ. DOES NOT APPEAR TO BE ANY SIGNIFICANT LARGE SCALE
FORCING TO HELP FOCUS STORMS.  THE ONLY AREA THAT MAY HAVE SOME WEAK
FORCING IS ALONG AN AXIS FROM SRN ESMERALDA/NYE COUNTIES NEWD WHERE
DEBRIS CLOUDS AND ISOLATED SHOWERS/THUNDERSTORMS EXIST...PERHAPS
ENHANCED BY SOME SPEED DIVERGENCE AND STRETCHING ALONG SHEAR AXIS.

AS HAS BEEN THE CASE PAST SEVERAL DAYS...NGM APPEARS TO HAVE THE BEST
INITIALIZATION OF FEATURES AND MOISTURE FIELDS. HIGH PRECIPITABLE
WATER PLUME (1.25 INCHES OR GREATER) SEEN ON GOES SOUNDER IMAGES FROM
SRN TIP OF NV SWD INTO GULF OF CA.  YUM SOUNDING INDICATES HIGH DEW
POINTS IN THE LOWER LAYERS (ALL SIMILAR TO NGM INITIALIZATION). TOUGH
CALL ON CONVECTION TODAY AS MOISTURE/INSTABILITY FIELDS SIMILAR TO
YESTERDAY BUT NO REAL FOCUS. DID NOTE WINDS ON DRA SOUNDING VEER WITH
HEIGHT FOR MODERATE SHEAR ENVIRONMENT FOR DECENT STORM STRUCTURE
TODAY. POSSIBLE THAT FOR THE FIRST TIME IN DAYS...STORMS THAT FORM ON
SPRING MOUNTAINS MAY PUSH INTO LAS VALLEY THIS AFTERNOON/EVENING.
SCATTERED STORMS LOOKS BEST AND NOT PLANNING ANY SIGNIFICANT CHANGES
TO FORECAST.

ON WEDNESDAY...MAIN TROF APPROACHES INCREASING MOIST SLY FLOW AND
BRINGING IN H3 JET WHICH PUTS MOST OF AREA IN RIGHT ENTRANCE REGION.
STRONGEST PVA/OMEGA FORECAST ACROSS NW AND NRN NV WITH BEST
DIVERGENCE APPROACHING SRN CA/SRN NV BY 00Z THU. ENTIRE AREA COVERED
BY SIGNIFICANT LOW LEVEL MOISTURE WHILE PRECIPITABLE WATER PLUME
MOVES NWD INTO ERN NV. STILL LOOKING LIKE WED WILL BE AN ACTIVE DAY
FOR THUNDERSTORMS. QUESTIONS I HAVE RIGHT NOW ARE HOW FAST WILL
TROUGH MOVE THROUGH GREAT BASIN THU AND WHETHER OR NOT MOISTURE WILL
BE SCOURED OUT TO PREVENT STORMS?  WILL TAKE ANOTHER SHOT AT THIS FOR
AFTERNOON PACKAGE.  LAS334. NEMETH