Area Forecast Discussion
Issued by NWS Las Vegas, NV

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000
FXUS65 KVEF 201706
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
1005 AM PDT WED AUG 20 2014

.SYNOPSIS...A LOW PRESSURE SYSTEM OVER SOUTHERN CALIFORNIA
WILL ACT UPON MONSOON MOISTURE IN PLACE LEADING TO A CHANCE OF
SHOWERS AND THUNDERSTORMS OVER SOUTHEAST CALIFORNIA...SOUTHERN
NEVADA AND NORTHWEST ARIZONA THROUGH THURSDAY. ON FRIDAY ANY MENTION
OF PRECIPITATION WILL BE CONFINED TO MOHAVE COUNTY. TEMPERATURES
WILL WARM OVER THE WEEKEND BACK TO NEAR NORMAL.
&&

.UPDATE...THE CLOSED UPPER LOW CIRCULATING ALONG THE SOUTHERN
CALIFORNIA COAST IS EXPECTED TO REMAIN NEARLY STATIONARY THROUGH
TONIGHT THEN MOVE INLAND TO THE EAST THURSDAY. THIS WILL FAVOR
THUNDERSTORMS OVER SOUTHWEST SAN BERNARDINO COUNTY TODAY. THE 12Z
LAS SOUNDING SHOWED CONDITIONS WERE QUITE UNSTABLE BUT SURFACE
DEWPOINTS HAVE DROPPED INTO THE 40S WITH A SLIGHT DOWNWARD TREND IN
PRECIPITABLE WATER VALUES. THE LATEST HIGH RES MODELS INDICATE
FAIRLY SPARSE CONVECTION TODAY BUT STILL ISOLATED THUNDERSTORMS CAN
BE EXPECTED DURING THE AFTERNOON AND EVENING ACROSS ALL BUT
ESMERALDA AND WEST CENTRAL NYE COUNTIES AND NORTHERN DEATH VALLEY.
THE GOING FORECAST LOOKS GOOD AND NO IMMEDIATE CHANGES NEEDED.
&&

.PREV DISCUSSION
309 AM PDT WED AUG 20 2014

.SHORT TERM...THROUGH FRIDAY NIGHT
RADAR MUCH QUIETER FROM 24 HOURS AGO. WE ARE MONITORING MAINLY RAIN
SHOWERS, ALTHOUGH EVER SO OFTEN ONE CELL WILL GENERATE A FEW
LIGHTNING STROKES.

CLOSED LOW JUST OFF THE SANTA BARBARA COAST WILL BE THE FEATURE OF
INTEREST TODAY AND AGAIN THURSDAY. MODELS HAVE COME INTO GOOD
AGREEMENT WITH THEIR HANDLING OF THE LOW THROUGH FRIDAY. CLOSED LOW
WILL STAY ALONG OR JUST OFF THE SOUTHERN CALIFORNIA COAST TODAY.
OUTSIDE OF SURFACE HEATING A STRENGTHENING JETSTREAK EAST OF THE LOW
CUTTING OVER SOUTHEAST CALIFORNIA AND NORTHWEST ARIZONA WILL PROVIDE
SOME ADDITIONAL LIFT. FOR SOUTHERN NEVADA, ADDITIONAL LIFT WILL
OCCUR IN AN AREA OF DIFFLUENCE ALOFT WITHIN THE NORTHEAST QUADRANT
OF THE CLOSED LOW. CLOSED LOW WILL MOVE AS FAR SOUTH AS SAN DIEGO
TONIGHT BEFORE BEGINNING TO OPEN UP AND PICKUP SPEED AS IT SHOULD BE
OVER THE LOWER COLORADO RIVER VALLEY BY LATE THURSDAY AFTERNOON. THE
MOST SIGNIFICANT DIFFERENCE IN THE MODELS COMES ON THURSDAY WITH
THEIR HANDLING OF MOISTURE ADVECTION OFF TROPICAL STORM LOWELL. NAM
BY FOR THE MOST AGGRESSIVE WITH THIS TROPICAL CONNECTION ADVECTING
MOISTURE FURTHER NORTH AND WEST INTO THE MOJAVE DESERT. GFS/ECMWF
TAKE MUCH OF THIS MOISTURE NORTHEAST ACROSS ARIZONA. THAT IS
SOMETHING WE WILL BE MONITORING VERY CLOSELY FOR SURE AS IT COULD
HAVE A SIGNIFICANT AFFECT ON RAINFALL INTENSITY THURSDAY. ON
THURSDAY NIGHT AND FRIDAY THE WEAKENING TROUGH WILL ACCELERATE EAST
ACROSS ARIZONA AS A DEEPER /EARLY FALL-LIKE/ TROUGH DEVELOPS OVER
THE PACIFIC NORTHWEST. MOISTURE WILL START TO BE SHUNTED EAST ON
FRIDAY EXCEPT IN MOHAVE COUNTY WHERE I DID KEPT A SLIGHT CHANCE OF
PRECIPITATION MENTIONED.

.LONG TERM...SATURDAY THROUGH WEDNESDAY NIGHT.

IN A MONTH THAT HAS LACKED ON BIG-TIME HEAT, WE APPEAR TO CATCH YET
ANOTHER BREAK COME SATURDAY AS THE LATEST OPERATIONAL MODELS NOW DIG
A DEEPER MID/UPPER LEVEL TROUGH NEVADA AND UTAH WITH THE BASE OF THE
TROUGH EXTENDING ALL THE WAY INTO SOUTHERN NEVADA. THERE MAY STILL
BE ENOUGH MID-LEVEL MOISTURE LEFT ACROSS THE EASTERN PORTIONS OF
MOHAVE COUNTY FOR A SHOWER OR THUNDERSTORM TO POP UP ON SATURDAY,
HOWEVER, A SHOWER OR THUNDERSTORM MAY ALSO POP UP IN THE AFTERNOON
OR EVENING ACROSS THE LINCOLN COUNTY PANHANDLE IN ASSOCIATION WITH
THE TROUGH AXIS. ONE CONCERN ON SATURDAY IS THAT MODELS MAY BE A
LITTLE UNDERDONE WITH SURFACE WINDS GIVEN THE DEPTH OF THE TROUGH.
WINDS WERE BUMPED UP SLIGHTLY ACROSS NORTHWESTERN SAN BERNARDINO
COUNTY AS WELL AS OVER THE HIGHER TERRAIN OF THE SOUTHERN GREAT
BASIN. THE MODELS SHOW A POOR ALIGNMENT OF THE WINDFIELDS WITH
HEIGHT, BUT GIVEN THE DEPTH OF THE TROUGH PROGGED IT WOULD NOT BE A
SURPRISE TO SEE FAVORED SPOTS GUST TO 25-35 MPH THEN. HIGHS SHOULD
BE A DEGREE OR TWO WARMER THAN WHAT WE SEE ON FRIDAY.

TYPICAL OF EARLY SEASON COOL SEASON TROUGHS, THIS TROUGH APPEARS
DEEP ENOUGH TO YIELD A SURFACE COLD FRONT PASSING THROUGH ACROSS THE
NORTHERN HALF OF THE AREA SATURDAY NIGHT INTO SUNDAY MORNING WITH A
WIND DIRECTION SHIFT NOTED. THE FRONT WILL LIKELY DAMPEN OUT BY THE
TIME IT GETS AS FAR SOUTH AS LAS VEGAS, THOUGH A BRIEF WIND SHIFT TO
THE NORTHWEST MAY TAKE PLACE INTO THE NW PART OF THE VALLEY THOUGH
IT MAY BE JUST AS EASILY MASKED BY THE DIURNAL NATURE OF WINDS AT
NIGHT. LOW TEMPS WERE LOWERED SEVERAL DEGREES CLOSER TOWARD THE
ECMWF MOS.

DRY NORTHWEST FLOW ALOFT LINGERS THROUGH TUESDAY AS A SECONDARY
TROUGH AXIS SWIPES ACROSS UTAH. THIS WILL KEEP AWAY ANY MONSOON
MOISTURE AND KEEP US UNDER ABUNDANT SUNSHINE OUTSIDE OF ANY CLOUDS
THAT PUSH NEAR THE UTAH BORDER TUESDAY WITH THE NEXT TROUGH. LOW
TEMPS WERE LOWERED SEVERAL DEGREES ACROSS THE NORTHERN CWFA WITH
HIGH TEMPS SHOWING A WARMING TREND AREA-WIDE THOUGH TEMPERED.
READINGS SHOULD RETURN ABOVE NORMAL BY TUESDAY. HOWEVER, NIGHTS WILL
BE MUCH MORE COMFORTABLE GIVEN THE LOWER HUMIDITY AND LOWER READINGS
OVERALL EVEN IN THE WARMER URBAN LOCATIONS IN THE MOJAVE DESERT.
CERTAINLY A SIGN WE ARE GETTING CLOSER TO SAYING HELLO TO FALL.
&&

.AVIATION...FOR MCCARRAN...CLOUDS AND ISOLATED RAIN SHOWERS WILL BE
ON THE INCREASE FROM THE SOUTHWEST DURING THE AFTERNOON. ISOLATED
THUNDERSTORMS WILL DEVELOP INTO ALL APPROACH CORRIDORS TODAY...WITH
THE LOWEST CHANCE IN THE BEATTY CORRIDOR. WINDS WILL FAVOR A EAST
DIRECTION SHIFTING TO SOUTH BY MID AFTERNOON TODAY BUT MAY BECOME
GUSTY AND ERRATIC IN DIRECTION DUE TO NEARBY SHOWERS OR
THUNDERSTORMS.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...ISOLATED/SCATTERED SHOWERS AND THUNDERSTORM WILL AFFECT
AREAS ROUGHLY EAST OF A LINE FROM BARSTOW TO HIKO ON TODAY. WINDS
WILL FAVOR A SOUTHEAST-SOUTH DIRECTION TODAY BUT WOULD BECOME GUSTY
AND ERRATIC IN DIRECTION DUE TO NEARBY SHOWERS OR THUNDERSTORMS.
&&

.SPOTTER INFORMATION STATEMENT...SPOTTERS SHOULD REPORT INSTANCES OF
FLASH FLOODING...STRONG GUSTY WINDS...HAIL...AND BLOWING DUST
THROUGH WEDNESDAY.
&&

$$

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

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