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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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