AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
400 PM PDT THU JUL 2 2009

.SYNOPSIS...A MOIST FLOW COMBINED WITH A SERIES OF UPPER LEVEL
DISTURBANCES WILL BRING SCATTERED SHOWERS AND THUNDERSTORMS TO PARTS
OF THE AREA THIS EVENING. SLIGHTLY DRIER AIR WILL BEGIN TO WORK INTO
THE AREA ON FRIDAY AND THIS WILL RESULT IN LESS IN THE WAY OF
THUNDERSTORMS. FURTHER DRYING WILL TAKE PLACE ON SATURDAY WITH THE
BEST CHANCES FOR THUNDERSTORMS THEN OVER MOHAVE AND LINCOLN
COUNTIES. DRY CONDITIONS ARE EXPECTED FROM SUNDAY THROUGH TUESDAY
THOUGH INCREASING SOUTHWEST WINDS ARE EXPECTED EACH DAY IN THE
AFTERNOON HOURS.
&&

.SHORT TERM...IT HAS BEEN A BUSY AFTERNOON ACROSS THE AREA WITH
SHOWERS AND THUNDERSTORMS AFFECTING PARTS OF THE MOJAVE DESERT AND
SOUTHERN GREAT BASIN. THE ACTIVITY WE HAVE BEEN SEEING THIS
AFTERNOON HAS DEVELOPED LARGELY ALONG A MOISTURE BOUNDARY LOCATED
NEAR THE CALIFORNIA-NEVADA BORDER SEPARATING DRY AIR TO THE WEST
FROM WHAT IS A SURGE OF MONSOONAL MOISTURE TO THE EAST. THIS
BOUNDARY HAS BASICALLY MARKED THE WESTERN EDGE OF CONVECTION AND TO
THE WEST OF IT LITTLE IF ANY ACTIVITY IS EXPECTED THIS EVENING AND
THUS LOWERED POPS DOWN ESPECIALLY WEST OF BARSTOW. FURTHER EAST A
SERIES OF UPPER LEVEL DISTURBANCES...ONE NOW OVER SOUTHEAST-CENTRAL
NEVADA  AND A SECOND ACROSS NORTHWEST NEVADA COMBINED WITH A PUSH OF
MOISTURE HAS RESULTED IN SCATTERED SHOWERS AND THUNDERSTORMS
DEVELOPING. THE MAIN HAZARD WITH STORMS THIS EVENING WILL BE LOCALLY
HEAVY DOWNPOURS DUE TO THE HIGH MOISTURE CONTENT OF THE AIR EAST OF
THE AFOREMENTIONED MOISTURE BOUNDARY. IN THIS AREA PWATS OF 0.75
INCHES TO 1.5 INCHES ARE CURRENTLY IN PLACE AND THIS WILL ALLOW FOR
THE HEAVIEST STORMS TO UNLOAD RAINFALL AMOUNTS IN EXCESS OF 0.5 TO 1
INCH OF RAIN IN LESS THAN AN HOUR. THE DRY LOW-LEVELS IN PLACE WILL
ALSO AID IN ALLOWING FOR GUSTY WINDS WITH THE STRONGEST STORMS.
ADDITIONALLY A FEW STRONGER STORMS WILL ALSO HAVE THE POTENTIAL FOR
HAIL. RADAR HAS BEEN SHOWING SOME RATHER HIGH VIL VALUES OF 40 OR
GREATER THIS AFTERNOON...BUT MDCRS SOUNDINGS FROM LAS VEGAS HAVE
INDICATED THE FREEZING LEVEL IS AROUND 15000 FEET. THUS SOME HAIL
MAY MAKE IT TO THE SURFACE...BUT IN REALITY MUCH OF THE HAIL WILL
MELT BEFORE REACHING THE GROUND AND THUS FALL AS HEAVY RAIN...AND
THIS WILL INCREASE THE POTENTIAL OF HEAVY DOWNPOURS TAKING PLACE. AS
THE DISTURBANCES MOVE NORTHEAST AROUND THE UPPER RIDGE THIS EVENING
AND WE LOOSE HEATING CONVECTION WILL BEGIN TO WIND DOWN. CLOUDS WILL
CLEAR OUT OF SOMEWHAT TONIGHT BUT WITH A SOUTHERLY FLOW IN PLACE
HUMIDITY VALUES WILL NOT LOWER MUCH OVER LAST NIGHT.

FOR TOMORROW THE FLOW ALOFT GOES MORE SOUTHWESTERLY AND THIS WILL
BRING DRIER AIR INTO THE AREA WHICH WILL BE MOST PRONOUNCED IN THE
WEST. PWATS LOWER BY A GOOD HALF AN INCH AREAWIDE AND THIS SHOULD
HELP TO ELIMINATE THE POTENTIAL FOR CONVECTION IN MOST OF THE
WESTERN CWFA. FURTHER EAST ENOUGH MOISTURE HANGS ON AND A FEW WEAK
RIPPLES EXIST IN THE 500 MB FLOW...BUT WITH LESS MOISTURE AROUND THE
THOUGHT IS THAT THERE SHOULD BE LESS IN THE WAY OF CONVECTION IN THE
AFTERNOON. THE BEST MOISTURE FLUX AND INSTABILITY SUPPORTS THE BEST
POPS EAST OF LAS VEGAS. TEMPS WILL WARM A FEW DEGREES IN MOST AREAS.

IT LOOKS LIKE WE GET EVEN MORE DRYING FOR SATURDAY AS THE FLOW TURNS
EVEN MORE TO THE WEST. PWATS FALL BELOW AN INCH ACROSS MOST OF THE
AREA. SUSPECT JUST ENOUGH MOISTURE STILL EXIST OVER MOHAVE COUNTY
AND LINCOLN COUNTY TO POP A FEW THUNDERSTORMS IN THE AFTERNOON.
TEMPS WILL BEGIN TO WARM A FEW DEGREES AS WE DRY OUT AND THUS EXPECT
NEAR SEASONAL HIGH TEMPS FOR THE FOURTH.

.LONG TERM...A BROAD UPPER LOW OFF THE PAC NW COAST WILL ESSENTIALLY
BRING IN ENOUGH WESTERLY FLOW TO ESSENTIALLY ELIMINATE THE CHANCES
FOR CONVECTION AREAWIDE FROM SATURDAY NIGHT THROUGH THURSDAY.
INITIALLY TEMPS WILL WARM ON SUNDAY AND MONDAY AS SOME SHORT WAVE
RIDGING DEVELOPS OVER THE FOUR CORNERS REGION. 700 MB TEMPS RISE TO
+14C TO +16C ACROSS THE AREA...SUPPORTING TEMPS A FEW DEGREES ABOVE
NORMAL. THEN AS THE BROAD LOW OFFSHORE APPROACHES TEMPS WILL DROP TO
OR BELOW NORMAL BY WEDNESDAY AS HEIGHTS FALL. STARTING SUNDAY
AFTERNOON AND CONTINUING THROUGH THURSDAY SOUTHWEST WINDS WILL
INCREASE EACH AFTERNOON AND THEN WEAKEN AT NIGHT DUE TO THE
APPROACHING TROUGH AXIS OFFSHORE. WE COULD SEE SOME SUSTAINED WINDS
OF 15-25 MPH EASILY AS EARLY AS TUESDAY.
&&

.AVIATION...FOR MCCARRAN...SCATTERED THUNDERSTORMS HAVE DEVELOPED
SOUTH AND EAST OF THE LAS VEGAS VALLEY AND COVERAGE WITHIN THE
VALLEY IS EXPECTED TO INCREASE BY 5 PM. STORMS IN THIS ENVIRONMENT
HAVE HAD A HISTORY OF PRODUCING VERY HEAVY RAIN IN A SHORT PERIOD OF
TIME SO VISIBILITY REDUCTION IS A POSSIBILITY. IN ADDITION...GUSTY
OUTFLOW WINDS ARE ANTICIPATED...GENERALLY FROM A SOUTH TO NORTHWEST
DIRECTION. CIGS WILL BEGIN TO LOWER ONCE AGAIN AS THE STORMS MOVE
INTO THE VALLEY.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...SCATTERED THUNDERSTORMS ARE EXPECTED THROUGH THE REST
OF THE AFTERNOON AND INTO THE EVENING HOURS. THEY WILL BE CAPABLE OF
PRODUCING WIND GUSTS UP TO 40 KTS AND VERY HEAVY RAIN IN A SHORT
PERIOD OF TIME CREATING REDUCED VISIBILITIES. CLOUD BASES WILL
GENERALLY BE AOA 8KFT. WINDS SHOULD REMAIN BELOW 12KTS AWAY FROM
THUNDERSTORMS.
&&

.VEF WATCHES/WARNINGS/ADVISORIES...
NV...NONE.
AZ...NONE.
CA...NONE.
&&