Flash Flood in Arizona, June 27, 2006

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LAS VEGAS NV
930 AM PDT TUE JUN 27 2006

.SYNOPSIS...AN AREA OF HIGH PRESSURE OVER NEVADA WILL SLOWLY SHIFT
TO THE FOUR CORNERS THE REST OF THE WEEK. THE RESULTING SOUTHEAST
FLOW WILL DRAW UP MOISTURE FROM MEXICO FOR ISOLATED TO SCATTERED
THUNDERSTORMS ACROSS THE REGION TODAY AND INCREASING STORM COVERAGE
WEDNESDAY AND THURSDAY.
&&

.UPDATE...ONLY VERY LIMITED CONVECTION SO FAR THIS MORNING EXCEPT
FOR A COUPLE OF SPOTS SOUTH OF SAN BERNARDINO COUNTY. CURRENT
PACKAGE LOOKS GOOD AS MAIN AXIS OF CONVECTION EXPECTED IN CALIFORNIA
PORTION OF CWA TODAY. MAY HAVE TO BUMP DOWN HIGHS A BIT DUE TO
CLOUD COVER BUT WILL HOLD OFF FOR ANOTHER HOUR OR TWO TO SEE HOW
TEMPERATURES REACT THIS MORNING.
&&

.PREVIOUS DISCUSSION FROM 3 AM PDT...SHORT TERM...LIMITED CONVECTION
WAS DEVELOPING EARLY THIS MORNING ALONG A LINE NEAR I-40 IN CENTRAL
MOHAVE COUNTY AND EXTENDING WEST INTO EASTERN SAN BERNARDINO COUNTY.
THIS WAS APPARENTLY IN RESPONSE TO A DISTURBANCE NEAR YUMA PRODUCING
MID LEVEL CONVERGENCE WITH THE NORTHERLY FLOW FROM THE HIGH WITH ITS
AXIS ROUGHLY ALONG THE CALIFORNIA/NEVADA BORDER. THIS COULD PRODUCE
ISOLATED THUNDERSTORMS THIS MORNING ACROSS SOUTHERN MOHAVE AND SAN
BERNARDINO COUNTIES. THE 00Z AND 06Z NAM AND GFS INDICATE THE RIDGE
AXIS SHIFTS SLIGHTLY EAST TODAY AND SHOULD EXTEND FROM LAKE TAHOE
DOWN THROUGH SOUTHERN NEVADA INTO SOUTHEAST ARIZONA. CONSIDERING
THAT MUCH OF MONDAYS CONVECTION OCCURRED NEAR THE RIDGE AXIS...THIS
SHOULD LEAD TO INCREASING COVERAGE ACROSS OUR FORECAST AREA
ESPECIALLY OVER INYO/SAN BERNARDINO AND POSSIBLY CLARK COUNTIES. THE
MAIN PATTERN SHIFT IS FORECAST TO OCCUR WEDNESDAY AS THE RIDGE AXIS
MIGRATES FARTHER EAST AND BRINGS SOUTHEASTERLY FLOW AND INCREASING
MOISTURE TO MOST OF THE FORECAST AREA. PRECIPITABLE WATER VALUES ARE
FORECAST TO INCREASE TO BETWEEN 1 AND 1.5 INCHES FOR SOUTHERN NEVADA
AND POINTS SOUTH. THE SOUTHERN SIERRA ALSO WILL SEE A SIGNIFICANT
INCREASE AS MOISTURE IS TRANSPORTED FROM MEXICO UP THROUGH SOUTHERN
CALIFORNIA. BOTH THE GFS AND NAM INDICATE THAT MOISTURE SHOULD STAY
IN PLACE OVER THE AREA THURSDAY AS AS A WEAK TROUGH DEVELOPS OVER
THE EASTERN PACIFIC. NEITHER MODEL INDICATES SUFFICIENT SOUTHWEST
FLOW DEVELOPING TO PUSH THE MOISTURE EAST. THE SOUTHERN SIERRA MAY
SEE SLIGHTLY LESS CONVECTION THURSDAY BUT CONFIDENCE IS NOT THAT
GREAT. IF ANYTHING...A SLIGHTLY STRONGER JET ALOFT AND SOME
INCREASING SHEAR MAY HELP ENHANCE CONVECTION...ESPECIALLY OVER
ESMERALDA...CENTRAL NYE AND LINCOLN COUNTIES THURSDAY AFTERNOON AND
EVENING.

.LONG TERM...MEDIUM RANGE MODEL PROGS KEEP UPPER HIGH PRESSURE
BASICALLY IN THE VICINITY OF ARIZONA OR JUST EAST OF THE CWA THRU
THE EXTENDED PERIOD. THIS GENERAL POSITION WOULD MAINTAIN MOIST FLOW
INTO AT LEAST THE EASTERN FORECAST AREA. BOTH THE GFS AND ECMWF SHOW
SOME MID LEVEL DRYING OVER THE WESTERN ONE THIRD OF THE CWA OVER THE
WEEKEND AND INTO EARLY NEXT WEEK....ESPECIALLY SUNDAY AND MONDAY.
HOWEVER...RIDGE REMAINS TOO STRONG FOR COMPLETE DRYING AS WEAK
IMPULSES FROM THE WEST ARE LIKELY TO LIFT TO THE NORTHEAST OVER THE
HIGH INSTEAD OF SUPPRESSING OR REPLACING THE RIDGING. KEPT POPS
CONFINED TO THE SOUTHERN AND EASTERN SECTIONS THESE DAYS AS A
COMPROMISE. ONLY MINOR TWEAKS MADE TO TEMPERATURES AS THE LATEST
MEX/MEN IS SIMILAR TO PREVIOUS GUIDANCE NUMBERS.

&&

.AVIATION...ISOLATED SHOWERS AND THUNDERSTORMS IN THE BARSTOW
CORRIDOR THIS MORNING WILL BECOME MORE SCATTERED BY AFTERNOON.
ISOLATED THUNDERSTORMS WILL ALSO DEVELOP IN THE BEATTY..MORMON MESA
AND PEACH SPRINGS CORRIDORS THIS AFTERNOON. THUNDERSTORMS WILL
LIKELY DEVELOP OVER THE MOUNTAINS WEST AND NORTH OF KLAS LATE THIS
MORNING AND AFTERNOON AND THERE IS A POSSIBILITY A THUNDERSTORM
COULD TEMPORARILY IMPACT KLAS WITH THE MAIN THREAT BEING STRONG
GUSTY AND VARIABLE WINDS. THE MOST FAVORABLE TIME WOULD BE
BETWEEN 22Z AND 02Z WHEN CONDITIONS ARE MOST UNSTABLE. TAFS AND
TWEBS ADEQUATELY DESCRIBE EXPECTED WEATHER CONDITIONS FOR AREA
TERMINALS. SEE TAFS FOR KLAS... KVGT... KDRA... KBIH... KDAG... KEED.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&

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

BELL/ADAIR/SALMEN

HTTP://WEATHER.GOV/LASVEGAS