Area Forecast Discussion
Issued by NWS Las Vegas, NV

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000
FXUS65 KVEF 071040
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
340 AM PDT TUE JUL 7 2015

.SYNOPSIS...MOIST AND UNSTABLE AIR REMAINS IN PLACE ACROSS MUCH OF
THE AREA WHICH ONCE HEATED WILL AGAIN TRIGGER SHOWERS AND
THUNDERSTORMS ACROSS MUCH OF THE AREA STARTING LATE THIS MORNING AND
LASTING INTO THIS EVENING. DRIER AIR WILL WORK IN FROM THE SOUTHWEST
SUPPRESSING THUNDERSTORM DEVELOPMENT IN MUCH OF THE AREA ON
WEDNESDAY EXCEPT FOR INYO COUNTY AND PARTS OF ESMERALDA AND NORTHERN
LINCOLN COUNTIES. AN AREA OF LOW PRESSURE WILL CROSS THE AREA ON
THURSDAY AND INCREASE THE POTENTIAL AGAIN FOR SHOWERS AND
THUNDERSTORMS NORTH OF INTERSTATE 15. MOST AREAS WILL BE DRY FRIDAY
INTO THIS WEEKEND. TEMPERATURES WILL REMAIN BELOW NORMAL. &&

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT.

FIRST OFF, FYI, OUR RADAR WILL BE DOWN THROUGH AT LEAST THIS
MORNING DUE TO A WEATHER-RELATED COMMUNICATIONS ISSUE. PLEASE USE
THE ADJACENT WSR-88D RADARS AS WELL AS THE TERMINAL DOPPLER WEATHER
RADAR (TLAS) FROM MCCARRAN AIRPORT FOR ANY RADAR MONITORING.
DETAILED UPDATES ON THE RADAR STATUS CAN BE FOUND THROUGH THE TEXT
STATUS MESSAGE (PRODUCT: RNOFTMESX) AVAILABLE ON OUR WEBPAGE.

A WEAK MID-LEVEL FEATURE (WEAK 500MB WAVE AND ASSOCIATED POTENTIAL
VORTICITY MAXIMUM) THAT FORMED YESTERDAY MORNING AND WAS LIKELY A
DRIVER IN YESTERDAY EVENING`S STORM THAT PRODUCED A PHOTOGRAPHIC
RAIN SHAFT IN VEGAS HAS MOVED EAST INTO UTAH EARLY THIS MORNING.
THIS FEATURE HAS TOUCHED OFF A FEW SHOWERS FROM WHAT WE CAN SEE ON
NEARBY RADARS IN EASTERN LINCOLN AND NORTHERN MOHAVE COUNTIES AS
WELL AS NORTHEAST CLARK COUNTY. MOST OF THIS ACTIVITY SHOULD GO AWAY
BY LATER THIS MORNING, BUT I DID ADJUST UP POPS HERE TO ACCOUNT FOR
THIS EARLY MORNING ACTIVITY.

OVERALL TODAY, THE MAIN PLAYERS THAT WERE AROUND 24 HOURS AGO ARE
STILL THERE. WE STILL HAVE A MID/UPPER LEVEL LOW OFF THE COAST OF
CALIFORNIA AND A MOIST-DRY INTERFACE STILL IN PLACE WEST OF THE
CALIFORNIA-NEVADA BORDER. EAST OF THIS LINE REMAINS THE MOIST AIR
WITH DRIER AIR STILL ATTEMPTING TO MOVE IN FROM THE SOUTHWEST. THE
LATEST OPERATIONAL MODELS ON THE 00Z RUNS AGAIN BRING ANOTHER WEAK
RIPPLE ALONG WITH A WEAK PV MAXIMUM UP ACROSS INYO COUNTY LATER THIS
MORNING INTO THIS AFTERNOON. THIS MAY AGAIN HELP ENHANCE CONVECTION
ACROSS INYO COUNTY TODAY. IN ADDITION, DAYTIME HEATING AND TERRAIN
WILL ALSO HELP TO DRIVE CONVECTION. ACTIVITY SHOULD AGAIN GET GOING
BY LATER THIS MORNING INTO THIS AFTERNOON AND THEN SLOWLY END THIS
EVENING. THERE IS SLIGHTLY MORE STABLE AIR SHOWN BY THE MODELS
ACROSS SAN BERNARDINO COUNTY THIS AFTERNOON, MAINLY AROUND BARSTOW
AND THE MORONGO BASIN, AND THUS IT LOOKS LIKELY THESE AREAS SHOULD
STAY FREE OF ANY SHOWER OR THUNDERSTORM ACTIVITY TODAY.

WHAT HAS BEEN A FOCUS FOR CONVECTION THE LAST TWO DAYS AND STILL
HANGS AROUND FOR TODAY IS THE MOIST-DRY INTERFACE OR SO CALLED
"DESERT DRY LINE". THIS DIFFERENTIAL MOISTURE BOUNDARY HAS HELPED
SPARK SOME VIGOROUS CONVECTION THAT HAS BEEN EFFICIENT IN PRODUCING
HEAVY RAIN (AND THUS TRIGGERING FLASH FLOODING) THE LAST TWO DAYS. I
REALLY DO NOT SEE ANYTHING DIFFERENT FOR TODAY. AS A RESULT, BASED
ON THE ARW, NMM AND WRF WHICH HAVE HAD A GREAT HANDLE ON WHAT AREAS
WILL SEE ACTIVITY THE LAST TWO DAYS, I USED THESE AS A GUIDE FOR
WHERE TO PLACE SHOWERS AND THUNDERSTORMS FOR TODAY BUT RAMPED UP
POPS CONSIDERABLY GIVEN THE MODELS OVERALL HAVE BEEN UNDOING POPS ON
THE COURSER LARGER SCALE MODELS MINUS THE WRF THE LAST TWO DAYS.
MODEL PWATS ARE FORECAST TO REMAIN AT OR ABOVE AN INCH FROM LAS
VEGAS ON SOUTH AND EAST WITH VALUES AROUND THREE-QUARTERS OF AN INCH
ELSEWHERE AWAY FROM THE FAR SOUTHWEST CWFA. AS A RESULT OF WHAT WE
HAVE SEEN THE LAST TWO DAYS, WE OPTED TO ISSUE A FLASH FLOOD WATCH
FOR ALL OF THE AREA EXCEPT NORTHWEST SAN BERNARDINO, SOUTHERN SAN
BERNARDINO AND SOUTHERN MOHAVE COUNTIES FOR THIS AFTERNOON AND
EVENING. NOT ALL AREAS IN THE WATCH WILL SEE STORMS BUT THE BETTER
STORMS THAT GET GOING TODAY WILL BE RIPE AGAIN TO UNLOAD HEAVY RAIN
AND POSSIBLY TRIGGER FLASH FLOODING ESPECIALLY IF THEY IMPACT ANY
LOW-LYING OR TERRAIN SENSITIVE AREAS.

THE LOW OFFSHORE WILL WORK CLOSER TO THE COAST TONIGHT AND THIS WILL
SPREAD DRIER AND MORE STABLE AIR OVERMUCH OF THE AREA FOR TOMORROW
AS A LARGE DRY SLOT MOVES ON IN. THE BEST AREA AT RISK FOR SHOWERS
AND THUNDERSTORMS WILL BE ACROSS INYO AND WESTERN ESMERALDA COUNTY.
ACTIVITY FROM TODAY MAY LINGER THROUGH TONIGHT AND LAST INTO
TOMORROW MORNING IN THE PANHANDLE OF LINCOLN COUNTY.

THINGS LOOK TO TREND BACK UP FROM THURSDAY AS THE LOW MOVES ACROSS
THE AREA ACCOMPANIED BY A 100 KT+ JET STREAM AT 250 MB MOVING
NORTHEAST ACROSS SOCAL. THIS JET IS ABOUT 3-4 STANDARD DEVIATIONS
ABOVE NORMAL FOR JUNE (YES THIS MAP LOOKS LIKE A WINTER TIME PATTERN
WITH THIS FEATURE). THE COMBINATION OF THE LIFT FROM THE JET AND THE
LOW ALONG WITH THE COLD POOL ALOFT OVERHEAD SHOULD LEAD TO AN UPTICK
IN CONVECTION ACROSS MUCH OF THE AREA ON THURSDAY. THE BIG QUESTION
FOR NOW IS HOW MUCH. WE INCREASED POPS NORTH OF INTERSTATE 15 GOING
30-40 PERCENT IN MOST AREAS. IT APPEARS LAS VEGAS WILL BE ON THE
EDGE OF THE BEST INSTABILITY AND THE FLOW WILL FAVOR STORMS HEADING
EAST SO POPS WERE MAINLY PLAYED UP ON THE WEST SIDE OF THE VALLEY.
THERE IS ALSO SOME POTENTIAL WITH THIS SYNOPTIC SET-UP FOR MORE
ORGANIZED STORMS TO FORM WHICH WOULD INCREASE THE SEVERE POTENTIAL.

TEMPS STAY BELOW NORMAL. LAS VEGAS FAILED TO HIT 100 YESTERDAY AND
SHOULD BE CLOSE TODAY. LOWER HEIGHTS AND COOLER AIR ALOFT WILL TURN
THE COOLING UP EVEN MORE CREATING A NICE BREAK FROM THE SUMMER
SWELTER.

.LONG TERM...FRIDAY THROUGH TUESDAY.

IT APPEARS WE WILL SEE THE FIRST BREAK IN THE MONSOON PATTERN ACROSS
MOST OF OUR FORECAST AREA BY FRIDAY AS A DRY SOUTHWEST FLOW DEVELOPS
BEHIND A SHORT WAVE TROUGH LIFTING OVER THE NORTHERN INTERMOUNTAIN
REGION. A MEAN TROUGH IS FORECAST TO HOLD ALONG THE WEST COAST
THROUGH EARLY NEXT WEEK WHICH WILL KEEP THE MAJORITY OF OUR FORECAST
AREA UNDER A DRY SOUTHWEST FLOW. THE SOUTHERN SIERRA AND ESMERALDA
COUNTY WILL STILL SEE A SLIGHT CHANCE OF THUNDERSTORMS FRIDAY AS
SOME MOISTURE LINGERS IN PROXIMITY TO THE CENTER OF THE WEST COAST
TROUGH.

THE MEDIUM RANGE MODELS INDICATE THE MID LEVEL HIGH WILL BECOME
CENTERED NEAR AROUND NEW MEXICO WHICH WILL BRING SOUTHEAST TO
SOUTHERLY FLOW AND LIMITED MOISTURE SPREADING BACK INTO NORTHWEST
ARIZONA AS EARLY AS SUNDAY. A SLIGHT CHANCE OF THUNDERSTORMS WAS
ADDED ACCORDINGLY. THIS PATTERN WILL LEAD TO WELL BELOW NORMAL
TEMPERATURES FRIDAY FOLLOWED BY A GRADUAL CLIMB BACK TO NORMAL
READINGS THROUGH THE WEEKEND AND EARLY NEXT WEEK.
&&

.AVIATION...FOR MCCARRAN...WINDS SHOULD FAVOR TYPICAL DIURNAL
DIRECTIONAL TRENDS THROUGH THIS EVENING AWAY FROM SHRA/TSRA ACTIVITY
OR ANY OUTFLOW BOUNDARIES. MAINLY FEW-SCT CLOUDS AOA 10K-15K FEET.
ONCE AGAIN TODAY SHRA/TSRA ARE EXPECTED TO DEVELOP IN AND AROUND THE
LAS VEGAS VALLEY AND IN THE APPROACH CORRIDORS MAINLY AFTER 20Z
TODAY. THIS ACTIVITY SHOULD DECREASE BETWEEN 03Z AND 05Z WEDNESDAY.
STORM MOVEMENT WILL BE NORTHEAST TO EAST AND THUS ACTIVITY MAY MAKE
IT INTO THE VALLEY ONCE AGAIN AND POTENTIALLY IMPACT THE AIRPORT
COMPLEX ITSELF. LOCALLY LOWER CIGS AND VSBY POSSIBLE IN AND NEAR ANY
SHRA/TSRA POTENTIALLY DROPPING TO MVFR OR LOWER.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...SHRA/TSRA SHOULD MAINLY DEVELOP BETWEEN 18Z AND 21Z
TODAY AND DIMINISH BETWEEN 03Z AND 07Z WEDNESDAY WITH THE GREATEST
ACTIVITY NORTH OF A LINE FROM KIYK-KLAS-KIGM. ONCE AGAIN GUSTY AND
ERRATIC WINDS AND CIGS AND VSBY REDUCED TO MVFR OR LOWER ARE
POSSIBLE IN AND NEAR SHRA/TSRA ACTIVITY. OTHERWISE EXPECT WINDS
FAVORING TYPICAL DIURNAL DIRECTIONAL TRENDS. GUSTS OF 20-25 KTS IN
THE AFTERNOON AND EVENING IN THE OWENS VALLEY AND IN AND NEAR KDAG.
&&

.SPOTTER INFORMATION STATEMENT...SPOTTERS ARE ENCOURAGED TO REPORT
ANY SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING
PROCEDURES.
&&

$$

SHORT TERM/AVIATION...STACHELSKI
LONG TERM...ADAIR

FOR MORE FORECAST INFORMATION...SEE US ON OUR WEBPAGE:

HTTP://WEATHER.GOV/LASVEGAS OR FOLLOW US ON FACEBOOK AND TWITTER



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