Flash Flood Watch 5, NWS Las Vegas, NV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
1018 AM PDT FRI AUG 1 2014

.SYNOPSIS...ISOLATED THUNDERSTORMS ARE EXPECTED AGAIN THIS
AFTERNOON. THUNDERSTORM CHANCES WILL INCREASE SATURDAY AND SUNDAY AS
DEEPER MOISTURE AND A POTENT UPPER LEVEL DISTURBANCE MOVE IN FROM
THE SOUTH.
&&

.UPDATE...THE 12Z LAS VEGAS SOUNDING SHOWS SUFFICIENT MOISTURE AND
INSTABILITY FOR ISOLATED CONVECTION OVER THE MOUNTAINS TODAY. THE
HIGH CENTER WILL BE OVER THE CA/NV LINE BETWEEN LAS VEGAS AND BISHOP
AND WILL PROVIDE LIGHT NORTH TO NORTHEAST FLOW ALOFT ACROSS SOUTHERN
NEVADA AND NORTHWEST ARIZONA. 12Z HIGH RES MODELS INDICATE THE
POTENTIAL FOR MORE THUNDERSTORM COVERAGE ACROSS CENTRAL NYE AND
LINCOLN COUNTIES AND SOUTHEAST MOHAVE COUNTY THIS EVENING. POP/WX
GRIDS WERE ADJUSTED UPWARD ACCORDINGLY.

THE 12Z NAM/GFS CONTINUE TO SHOW THE CLOSED LOW MOVING UP THE BAJA
PENINSULA WILL BEGIN TO INFLUENCE THE REGION WITH A MOISTURE
INCREASE AND UPWARD FORCING BEGINNING SATURDAY AFTERNOON THROUGH
SUNDAY FOR INCREASING THUNDERSTORM ACTIVITY WITH THE POTENTIAL FOR
HEAVY RAIN PRODUCING STORMS.
&&

.PREV DISCUSSION...
230 AM PDT FRI AUG 1 2014

.SHORT TERM...THROUGH SUNDAY NIGHT...SATELLITE AND AREA RADARS
SHOWED THE LAST OF THE CONVECTION EXITING LINCOLN AND MOHAVE
COUNTIES AS OF 2 AM. SURFACE OBS SHOWED MODERATELY HUMID AIR
/DEWPOINTS IN THE 40S AND 50S/ ACROSS THE CWA WITH MUCH MORE HUMID
AIR /DEWPOINTS IN THE 70S/ LURKING JUST TO THE SOUTH IN THE LOWER
VALLEYS OF THE SOUTHERN CALIFORNIA DESERTS. MID LEVEL HIGH PRESSURE
CENTERED NEARLY OVERHEAD THIS AFTERNOON WILL LIMIT INSTABILITY IN
THE CENTRAL CWA...WITH SLIGHTLY COOLER AIR ALOFT AROUND ITS
PERIPHERY ALLOWING FOR SLIGHTLY MORE UNSTABLE AIR IN THE FAR NORTH
AND FAR SOUTH...SO FOCUSED PRECIP CHANCES THERE. SATURDAY AND SUNDAY
ARE SHAPING UP TO BE A SIGNIFICANT CONCERN. SATELLITE LOOP SHOWED AN
UPPER LOW SPINNING NEAR THE SOUTHERN TIP OF THE BAJA...AND
PRECIPITABLE WATER SENSORS SHOWED VALUES IN EXCESS OF TWO INCHES IN
THAT REGION. OVER THE WEEKEND...THE UPPER LOW WILL WORK ITS WAY
NORTHWARD /POSSIBLY PHASING WITH A PIECE OF THE SHORTWAVE TROUGH
CURRENTLY OVER UTAH WHICH IS FORECAST TO MOVE SOUTH AND THEN WEST
AROUND THE AFOREMENTIONED HIGH CENTER/...ADVECTING IN THE DEEP
MOISTURE FROM THE SUBTROPICS. ONLY CONCERNS ARE TIMING OF THE
GREATEST CHANCE OF THUNDERSTORMS AND WHETHER ABUNDANT CLOUD COVER
MAY PUT A LID ON THINGS SUNDAY. EITHER WAY...A STORMY WEEKEND IS A
GOOD POSSIBILITY. DEEP MOISTURE AND CLOUD COVER WILL ALSO KEEP
TEMPERATURES WAY BELOW NORMAL FOR EARLY AUGUST.

.LONG TERM...MONDAY THROUGH THURSDAY...BY MONDAY MORNING THE UPPER
LEVEL LOW THAT WILL CREATE THIS WEEKEND'S UPTICK IN MONSOON ACTIVITY
WILL BE SITUATED SOMEWHERE IN THE VICINITY OF CENTRAL NEVADA.
ENHANCED MOISTURE [850-500MB MIXING RATIOS OF 6-8 G/KG] AND LI'S OF
0 TO -4 ARE EXPECTED TO BE IN PLACE BY MONDAY AFTERNOON ACROSS MOST
OF THE REGION EXCEPT PERHAPS SOUTHERN AND WESTERN SAN BERNARDINO
COUNTY. MODELS ARE IN FAIR AGREEMENT IN THE EXISTENCE OF A WEAK
40-60KT JET MOVING NORTH INTO CENTRAL/WESTERN ARIZONA AND ONE OR
MORE VORTICITY LOBES ROTATING AROUND THE LOW MONDAY. THESE FEATURES
HAVE THE POTENTIAL TO PROVIDE ENOUGH DYNAMICS FOR ONE MORE DAY OF
FAIRLY WIDESPREAD CONVECTION ACROSS THE REGION. THE EXTENT OF ANY
OVERNIGHT ACTIVITY IS MUCH LESS CERTAIN WITH SIGNIFICANT INTER-MODEL
DIFFERENCES IN THE AREAS OF FORCING AFTER SUNSET. THE PRIMARY
CONCERN WILL FLASH FLOODING FROM TRAINING STORMS AS STORM MOTION IS
FORECAST TO BE GENERALLY NORTHEAST AT 10-15 MPH.

FOR TUESDAY MORE DRYING IS EXPECTED FROM THE SOUTHWEST...HOWEVER I
DID EXPAND POPS A BIT FURTHER SOUTH AS THE GENERAL CONSENSUS SHOWS
SLOWER DRYING THAN WHAT WAS INDICATED 24 HOURS AGO. THE OVERALL
DRYING TREND IS EXPECTED TO CONTINUE WEDNESDAY AND THURSDAY WITH
PRECIP CHANCES BECOMING INCREASINGLY LIMITED TO AN AREA NORTH OF AN
INDEPENDENCE-RACHEL-MESQUITE-GRAND CANYON SKYWALK ARCH. HAVE ALSO
LEFT IN SLIGHT CHANCE POPS OVER THE CLARK COUNTY MOUNTAINS THROUGH
THE WEEK.

TEMPERATURES ARE EXPECTED TO WARM FROM 5-8 DEGREES BELOW NORMAL
MONDAY TO ONLY A COUPLE DEGREES BELOW NORMAL BY WEDNESDAY.
&&

.AVIATION...FOR MCCARRAN...THERE IS AN OUTSIDE CHANCE OF A
THUNDERSTORM OVER THE MOUNTAINS NEAR THE TERMINAL THIS
AFTERNOON...WITH BETTER CHANCES IN THE PEACH SPRINGS CORRIDOR. WINDS
ARE LIKELY TO BE A HEADACHE TODAY...WITH EAST OR SOUTHEAST FOR MUCH
OF THE AFTERNOON. IT COULD BE A DIFFICULT WEEKEND...AS THERE WILL BE
INCREASING CHANCES FOR THUNDERSTORMS WITH THE PRIMARY CONCERNS BEING
VERY HEAVY RAIN AND ERRATIC GUSTY WINDS.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...THERE WILL BE A SLIGHT CHANCE OF THUNDERSTORMS THIS
AFTERNOON AND EVENING MAINLY IN MOHAVE COUNTY AND THE HIGHER TERRAIN
OF ESMERALDA AND NORTHERN INYO COUNTIES. THUNDERSTORM CHANCES WILL
INCREASE AREAWIDE THIS WEEKEND...WITH THE MAIN CONCERNS BEING VERY
HEAVY RAIN AND ERRATIC GUSTY WINDS.
&&

.SPOTTER INFORMATION STATEMENT...SPOTTER ACTIVATION IS NOT EXPECTED
TODAY. SPOTTER ACTIVATION MAY BE NEEDED OVER THE WEEKEND FOR
THUNDERSTORMS WITH VERY HEAVY RAIN AND POTENTIAL FLASH FLOODING.
&&

UPDATE...ADAIR
PREV DISCUSSION...MORGAN/WOLCOTT

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