Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 012232 CCA
AFDVEF

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE LAS VEGAS NV
319 PM PDT FRI AUG 1 2014

.SYNOPSIS...INCREASING THUNDERSTORM COVERAGE WITH THE POTENTIAL FOR
HEAVY RAIN CAN BE EXPECTED SATURDAY AND SUNDAY AS DEEPER MOISTURE
AND A POTENT UPPER LEVEL DISTURBANCE MOVE IN FROM THE SOUTH. THIS
WILL BE FOLLOWED BY A DRYING TREND FROM SOUTHWEST TO NORTHEAST
EARLY NEXT WEEK.
&&

.SHORT TERM...THROUGH SUNDAY NIGHT...ISOLATED TERRAIN DRIVEN
THUNDERSTORMS THIS AFTERNOON WILL BECOME MORE EXTENSIVE SATURDAY
AFTERNOON THROUGH SUNDAY AS ABUNDANT MOISTURE AND A LARGE UPPER
LOW MOVE UP FROM BAJA CALIFORNIA AND NORTHWEST MEXICO. AS THE CLOSED
LOW APPROACHES SATURDAY AFTERNOON...CYCLONIC FLOW ON ITS NORTHERN
PERIPHERY WILL CONVERGE WITH ANTICYCLONIC FLOW AROUND A MID LEVEL
HIGH CENTERED OVER CENTRAL NEVADA. THE 12Z NAM INDICATES A
SUBSTANTIAL PUSH OF LOW LEVEL MOISTURE UP THROUGH SOUTHEAST
CALIFORNIA...NORTHWEST ARIZONA AND SOUTHERN NEVADA BY SATURDAY
AFTERNOON WHILE THE GFS AND ECMWF ARE LESS AGGRESSIVE.
HOWEVER...CONVECTIVE COMPLEXES HAVE BEEN DEVELOPING ON THE NORTHERN
SIDE OF THE UPPER LOW THE PAST COUPLE EVENINGS AND THERE WILL LIKELY
BE ANOTHER ONE THIS EVENING WHICH WILL HELP PUSH MOISTURE OUR WAY.
THE NAM/GFS/ECMWF ARE IN GOOD AGREEMENT AT LIFTING THE CENTER OF THE
LOW INTO SOUTHERN CALIFORNIA BY 12Z SUNDAY. POSITIVE VORTICITY
ADVECTION WILL OCCUR SATURDAY NIGHT ACROSS THE AREA FROM LAS VEGAS
SOUTHWARD WHICH SHOULD PROVIDE BROAD UPWARD FORCING TO THE MOIST AND
UNSTABLE AIR MASS STREAMING INTO THE REGION. NOCTURNAL THUNDERSTORMS
WILL LIKELY BE AROUND OVER THE AREA FROM CLARK COUNTY SOUTHWARD. THE
GFS AND ECMWF SOLUTIONS LIFT THE LOW UP ACROSS CENTRAL CALIFORNIA
INTO WESTERN NEVADA SUNDAY AND SUNDAY NIGHT WITH SUBSTANTIAL
MOISTURE AND UPWARD FORCING ACROSS INYO...NYE AND ESMERALDA
COUNTIES. THIS SCENARIO WILL BE FAVORABLE FOR EXTENSIVE COVERAGE OF
HEAVY RAIN PRODUCING THUNDERSTORMS GRADUALLY EXPANDING FROM SOUTH TO
NORTH ACROSS  THE REGION FROM FROM SATURDAY AFTERNOON THROUGH SUNDAY
AFTERNOON. A FLASH FLOOD WATCH HAS BEEN ISSUED FOR THE ENTIRE AREA
ACCORDINGLY. NO SIGNIFICANT CHANGES TO THE FORECAST WERE MADE BEYOND
SUNDAY NIGHT.

.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...ISOLATED THUNDERSTORMS AROUND SOUTHERN
NEVADA COULD PRODUCE OUTFLOW BOUNDARIES THIS EVENING WITH ABRUPT
CHANGES IN WIND DIRECTIONS BUT CONFIDENCE REGARDING ANY PARTICULAR
DIRECTION. OTHERWISE...PREVAILING WINDS WILL BE FROM THE SOUTH TO
SOUTHWEST THIS EVENING THROUGH THE SATURDAY MORNING. IT COULD BE A
DIFFICULT WEEKEND...AS THERE WILL BE INCREASING CHANCES FOR
THUNDERSTORMS AROUND SOUTHERN NEVADA SATURDAY AFTERNOON THROUGH
SUNDAY WITH THE PRIMARY CONCERNS BEING VERY HEAVY RAIN AND ERRATIC
GUSTY WINDS.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...ISOLATED THUNDERSTORMS AROUND THE REGION WILL GRADUALLY
DISSIPATE THIS EVENING. THUNDERSTORM CHANCES WILL INCREASE AREAWIDE
SATURDAY AFTERNOON THROUGH SUNDAY...WITH THE MAIN CONCERNS BEING
VERY HEAVY RAIN AND ERRATIC GUSTY WINDS.
&&

.SPOTTER INFORMATION STATEMENT...SPOTTER ACTIVATION MAY BE NEEDED
OVER THE WEEKEND FOR THUNDERSTORMS WITH VERY HEAVY RAIN AND
POTENTIAL FLASH FLOODING.
&&

SHORT TERM/AVIATION...ADAIR
LONG TERM...WOLCOTT

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