Area Forecast Discussion
Issued by NWS Las Vegas, NV

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000
FXUS65 KVEF 310952
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
252 AM PDT FRI JUL 31 2015

.SYNOPSIS...LINGERING MOISTURE AND INSTABILITY WILL RESULT ONCE
AGAIN IN SHOWERS AND THUNDERSTORMS DEVELOPING ACROSS PARTS OF THE
AREA FROM LATE THIS MORNING THROUGH THIS EVENING. LOCALLY HEAVY
RAINFALL IS POSSIBLE WHICH COULD RESULT IN FLASH FLOODING. THE
CHANCE FOR SHOWERS AND THUNDERSTORMS WILL DECREASE ACROSS AREAS
SOUTH AND WEST OF LAS VEGAS GRADUALLY OVER THE WEEKEND AS DRIER AIR
STARTS TO WORK ON IN. GENERALLY DRY CONDITIONS ARE EXPECTED FROM
MONDAY ONWARD. TEMPERATURES WILL REMAIN NEAR NORMAL.
&&

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT.

MOST OF THE SHOWER ACTIVITY HAS DECREASED ACROSS THE AREA EARLY THIS
MORNING ALTHOUGH AREA RADARS SHOW A FEW LIGHT RETURNS STILL AROUND.
WE STILL HAVE A LARGE AREA OF CLOUD COVER AROUND MAINLY NORTH OF
INTERSTATE 40 ALTHOUGH GENERALLY THIS IS HOLDING `AS IS` OR WE ARE
SEEING A DECREASE IN BRIGHTNESS IN CLOUD TOP TEMPERATURES ON
INFRARED SATELLITE AND THUS WE SHOULD SEE THIS AREA SLOWLY THIN
THROUGH THE REST OF THE MORNING. ONCE AGAIN, THIS CLOUD COVER WILL
LIKELY BE THE LIMITING FACTOR TODAY AS IT WILL HAMPER HEATING IN
SOME AREAS THIS MORNING IF IT IS SLOW TO ERODE.

OVERALL TODAY WE REMAIN IN A SOUTHEAST FLOW ALOFT AND WE REMAIN
QUITE MOIST. IPW SENSORS SHOW PWATS BETWEEN 0.60 AND 1.50 INCH
ACROSS THE AREA (LOWEST FAR NORTH AND HIGHEST SOUTH) SO THERE IS
SUFFICIENT MOISTURE STILL TO WORK WITH. HOWEVER, UNLIKE YESTERDAY
WHEN WE HAD SOME DISTURBANCES IN THE MID-LEVELS OF THE ATMOSPHERE
AROUND, THESE HAVE MOVED ON NORTH, WITH THE MOST NOTICEABLE FEATURE
THE WAVE THAT CROSSED SOCAL YESTERDAY WHICH IS NOW NEAR LAKE TAHOE
(AND NOTICEABLE STILL ON WATER VAPOR AND IN THE HEIGHT AND VORTICITY
FIELDS AT 500 MB). THUS WHAT WILL DRIVE CONVECTION TODAY WILL BE
WHATEVER HEATING WE GET, TERRAIN AND SOME LEFTOVER BOUNDARIES
FLOATING AROUND ACROSS THE AREA AS WE HAD SEVERAL OUTFLOWS MOVE ON
THROUGH LAS VEGAS ALONE. ACTIVITY SHOULD INITIATE STARTING BY LATER
THIS MORNING OVER THE HIGHER TERRAIN OR ON ANY OLD BOUNDARIES AND
THEN MOVE MAINLY WEST TO NORTHWEST GIVEN THE 700-500 MB FLOW IS EAST
TO SOUTHEAST. HOWEVER, WIND SPEEDS ARE LIGHTER IN THIS LAYER TODAY.
THUS, WE MAY SEE SOME SLOWER MOVING ACTIVITY. GIVEN THE UNLOAD
FACTOR IS STILL THERE PER PWATS WE ARE CURRENTLY SEEING AND PROGGED
TO SEE THIS AFTERNOON AND EVENING AS WELL AS THE LIGHTER STEERING
FLOW, A FLASH FLOOD WATCH WAS ISSUED FOR MUCH OF THE AREA FROM LATE
THIS MORNING THROUGH THIS EVENING. THE EXCEPTION WAS ALL OF SOUTHERN
SAN BERNARDINO COUNTY AS THIS AREA IS EXPECTED TO SEE DRIER AND MORE
STABLE AIR PUSH IN TODAY FROM THE SOUTHWEST. AS A RESULT, I LOWERED
POPS HERE ESPECIALLY TOWARD THE MORONGO BASIN FOR THIS AFTERNOON AND
EVENING. IN SOME CASES, THE MENTION OF SHOWERS AND THUNDERSTORMS WAS
YANKED ALTOGETHER.

GIVEN TEMPS YESTERDAY AGAIN GOT WARMER THAN EXPECTED (LAS VEGAS
REACHED 106 AT MCCARRAN WHICH IS THE FIRST 105 OR PLUS HIGH TEMP
SINCE JULY 3RD), I LEANED WARMER FOR HIGHS TODAY AND BUMPED SOME
SPOTS UP, ESPECIALLY WHERE CONVECTION IS NOT EXPECTED TO BE AS
ABUNDANT. SHOWER AND THUNDERSTORM ACTIVITY SHOULD END THIS EVENING
WITH THE LOSS OF HEATING.

OVER THE WEEKEND WE WILL REMAIN IN A SOUTH TO SOUTHEAST FLOW ALOFT
ON SATURDAY, HOWEVER, THIS WILL START TO TRANSITION MORE TO THE
SOUTHWEST ON SUNDAY IN RESPONSE TO A MID/UPPER LEVEL LOW THAT CAN BE
SEEN ALREADY ON WATER VAPOR OFF THE COAST OF CALIFORNIA. THIS LOW
WILL WORK CLOSER TO THE COAST BY SUNDAY AFTERNOON. AS A RESULT,
DRIER AND MORE STABLE AIR IS EXPECTED TO SLOWLY SPREAD NORTHEAST
ACROSS THE AREA. AREAS OUT NEAR BARSTOW AND THE MORONGO BASIN SHOULD
STAY DRY ALL WEEKEND, WHILE THE BEST CHANCES FOR SHOWERS AND
THUNDERSTORMS WILL BE NORTH AND EAST OF LAS VEGAS, INCLUDING THE
SOUTHERN SIERRA. WITH A MOIST-DRY INTERFACE SPREADING EAST AND A
POTENTIAL WEAKNESS AND ASSOCIATED PV MAX ROTATING NORTH ACROSS THE
AREA ON SATURDAY, THIS MAY HELP TO HAVE A BETTER FOCUS FOR SHOWERS
AND THUNDERSTORMS. POPS WERE ADJUSTED ON UP BY 10-20 PERCENT FROM
LAS VEGAS ON NORTH AND EAST. PWATS STILL ARE PROGGED BY THE GFS TO
REMAIN OVER AN INCH, SO FLASH FLOODING COULD STILL BE AN ISSUE AS
COULD GUSTY WINDS AND HAIL. BY SUNDAY, PWATS ARE EXPECTED TO FALL
BELOW AN INCH ACROSS THE ENTIRE AREA, SO THE FLASH FLOOD THREAT MAY
DECREASE A BIT. HOWEVER, WE GET THE ADDED FEATURE A 50 KT+ JET
STREAK AT 250 MB APPROACHING THE SOUTHERN SIERRA, WHICH WILL AID IN
LIFTING THE AIR BETTER. THUS, WE MAY STILL SEE SOME EFFECTIVE RAIN
PRODUCING STORMS. POPS WERE RAISED FOR SUNDAY IN THE EASTERN SLOPES
OF THE SOUTHERN SIERRA AND OWENS VALLEY GIVEN THIS AND THE SOUTHWEST
FLOW ALOFT WHICH WOULD PUSH ACTIVITY OFF THE CREST INTO THESE AREAS.
WE LEFT LAS VEGAS DRY FOR NOW, THOUGH THE FLOW COULD DRIVE ACTIVITY
OFF THE SPRING MOUNTAINS ON INTO THE VALLEY, SO THIS WILL NEED TO BE
WATCHED. GIVEN RECENT TRENDS, I WENT WARMER THAN MOST GUIDANCE ON
HIGH TEMPS EVEN THOUGH WE SEE A DROP IN HEIGHTS OVER THE WEEKEND.

.LONG TERM...MONDAY THROUGH FRIDAY.

THE LATEST MODEL GUIDANCE CONTINUES TO BE CONSISTENT IN TRENDING
TOWARD DRIER CONDITIONS IN THE LONG TERM PERIOD ACROSS MUCH OF THE
CWA. BY MONDAY MORNING...DRY SOUTHWEST FLOW IS EXPECT TO CONTINUE TO
INFILTRATE THE AREA...WITH THE ONLY REMAINING SIGNIFICANT MOISTURE
LINGERING AROUND NORTHERN INYO AND ESMERALDA COUNTIES. POPS WERE
TRENDED BACK AREA WIDE...BUT KEPT A CHANCE OF SHOWER AND
THUNDERSTORM ACTIVITY IN THE AFOREMENTIONED AREAS...ESPECIALLY THE
SIERRA AND WHITE MOUNTAINS OF INYO COUNTY THROUGH MONDAY AFTERNOON.
BY MID-WEEK...MOISTURE SHOULD BE SCOURED OUT OF MUCH OF THE CWA...AS
A SERIES OF UPPER LEVEL SHORTWAVES TRAVERSES THE GREAT
BASIN...COURTESY OF A DIGGING UPPER LEVEL LOW OFF OF THE COAST OF
BRITISH COLUMBIA. THIS PATTERN WILL YIELD DRIER AND SLIGHTLY WARMER
CONDITIONS INITIALLY...WITH INCREASED AFTERNOON BREEZES.

THERE ARE HINTS IN BOTH THE 00Z GFS AND ECMWF TONIGHT IN A POTENTIAL
STRONGER SHORTWAVE SWEEPING ACROSS THE GREAT BASIN IN THE WEDNESDAY
EVENING TO THURSDAY TIMEFRAME. THIS WOULD AID IN PULLING SUFFICIENT
MOISTURE BACK INTO AT LEAST MOHAVE COUNTY FOR LATE WEEK...WHICH
COULD SPELL A RETURN OF SHOWER AND THUNDERSTORM CHANCES. THIS WOULD
ALSO INTRODUCE A COOLING TREND AREA WIDE...WITH AFTERNOON HIGHS
COOLING BACK BELOW AVERAGE FOR EARLY AUGUST THROUGH THE END OF THE
WEEK. WITH THAT SAID...STANDARD TIMING AND ESPECIALLY STRENGTH
DIFFERENCES BETWEEN MODEL RUNS THIS FAR OUT IS ENOUGH TO KEEP
CONFIDENCE LOW IN ANY POTENTIAL SCENARIOS AT THIS TIME. STAY TUNED!
&&

.AVIATION...FOR MCCARRAN...WINDS TODAY WILL AGAIN FAVOR AN EASTERLY
DIRECTION FROM THE LATE MORNING INTO THE AFTERNOON THEN TRANSITION
SOUTH. SPEEDS WILL MAINLY BE 5-10 KTS. OUTFLOW FROM ANY SHRA/TSRA
COULD AGAIN CAUSE GUSTY AND ERRATIC WINDS AT KLAS. AGAIN THERE WILL
BE THE POTENTIAL FOR SHRA/TSRA IN THE DAGGETT, PEACH SPRINGS AND
BEATTY APPROACH CORRIDORS AS WELL AS IN THE MOUNTAINS IN AND AROUND
THE LAS VEGAS VALLEY. THE GENERAL STORM MOTION WILL BE SOUTHEAST TO
EAST, WHICH MEANS ANY ACTIVITY THAT FORMS OVER THE MCCULLOUGH RANGE,
MOJAVE NATIONAL PRESERVE OR LAKE MEAD AREA COULD DRIFT TOWARD THE
AIRPORT COMPLEX AND HAVE INCLUDED A VCTY TSRA IN THE TAF FOR THIS
AFTER 22Z TODAY THROUGH 04Z SATURDAY. SCT-BKN CLOUDS AOA 12K FEET
THROUGH TONIGHT.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...ONCE AGAIN TODAY SHRA/TSRA WILL BE AROUND ACROSS THE
ENTIRE AREA WITH ACTIVITY MAINLY OVER THE HIGHER ELEVATIONS. GUSTY
AND ERRATIC WINDS AND MVFR OR LOWER CIGS AND VSBY ARE POSSIBLE IN
AND NEAR ANY SHRA/TSRA. LOCAL MOUNTAIN OBSCURATIONS ARE POSSIBLE.
OTHERWISE EXPECT WINDS TO FAVOR TYPICAL DIURNAL DIRECTION AND SPEED
TRENDS WITH SCT-BKN CLOUDS AOA 8K-15K FEET.
&&

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

$$

SHORT TERM/AVIATION...STACHELSKI
LONG TERM...PULLIN

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