Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 172125
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
225 PM PDT WED SEP 17 2014

.SYNOPSIS...THE REMNANTS OF HURRICANE ODILE WILL TRACK EAST OF OUR
AREA THROUGH THURSDAY. A SURGE OF MOISTURE FROM THIS STORM WILL
INCREASE THE THREAT OF SCATTERED AFTERNOON THUNDERSTORMS AND FLASH
FLOODING FOR PORTIONS OF THE AREA. AN UPPER LEVEL DISTURBANCE WILL
MOVE INTO THE AREA ON THURSDAY EVENING TO BEGIN A DRYING TREND.
&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
THE SYNOPTIC PATTERN ACROSS THE SOUTHWESTERN CONUS IS QUITE COMPLEX
TODAY. WE HAVE AN UPPER LEVEL TROUGH IN THE PACIFIC...THE REMNANT
CIRCULATION OF ODILE ACROSS SOUTHERN ARIZONA...AND HIGH PRESSURE
CENTERED OVER UTAH. THE REMNANTS OF ODILE AND THE HIGH IN UTAH HAVE
COMBINED TO PROVIDE MORE OF A NORTHEASTERLY FLOW ALOFT ACROSS OUR
EASTERN FORECAST AREA...WHILE THE PACIFIC TROUGH IS PROVIDING
SOUTHWEST FLOW OVER OUR WESTERN COUNTIES. IN BETWEEN THESE TWO
AIRSTREAMS WE FIND A DEFORMATION ZONE.

A MOIST AND UNSTABLE AIR MASS REMAINS IN PLACE THIS
AFTERNOON...ESPECIALLY OVER THE EASTERN PORTION OF THE FORECAST
AREA. DIURNAL HEATING COMBINED WITH THE AFOREMENTIONED DEFORMATION
ZONE OVER THE FORECAST AREA WILL AID IN PROVIDING ADEQUATE FORCING
TO GENERATE THUNDERSTORMS. WE ALREADY HAVE THUNDERSTORMS ACROSS
PORTIONS OF MOST OF OUR COUNTIES. PRECIPITABLE WATER VALUES FOR MUCH
OF OUR EASTERN CWA ARE AT OR ABOVE 200 PERCENT OF NORMAL...NEARING
+3 STANDARD DEVIATIONS FOR THIS TIME YEAR. WITH THIS ANOMALOUSLY
MOIST ENVIRONMENT AND STORM COVERAGE EXPECTED TO INCREASE THROUGH
THE AFTERNOON, WILL CONTINUE THE FLASH FLOOD WATCH. THE CHANCE OF
THUNDERSTORMS WILL DECREASE TONIGHT...ALONG WITH THE FLASH FLOOD
THREAT. HOWEVER...WE WILL KEEP THE FLASH FLOOD WATCH AS IS TO
ACCOUNT FOR ACTIVITY INCREASING ONCE AGAIN TOMORROW.

THE PACIFIC TROUGH OFF THE CALIFORNIA COAST WILL MOVE INLAND
THURSDAY...PROVIDING MORE SOUTHWEST FLOW ACROSS A LARGER PORTION OF
THE FORECAST AREA. DRY AIR WILL START TO PUSH IN FROM THE WEST BUT
THERE WILL BE ENOUGH LIFT AND MOISTURE FOR SCATTERED TO NUMEROUS
SHOWERS AND THUNDERSTORMS FROM LINCOLN COUNTY SOUTHWARD THROUGH
CENTRAL CLARK...EASTERN SAN BERNARDINO...AND POINTS EAST. WITH THE
DRY AIR FILTERING IN FROM THE WEST...STORMS THAT DEVELOP ON THE
WESTERN MOISTURE GRADIENT COULD CONTAIN STRONGER WIND GUSTS. WILL
HAVE TO WATCH THIS FOR TOMORROW. WILL KEEP THE FLASH FLOOD WATCH IN
EFFECT FOR NOW...BUT STRONGER DRY AIR ADVECTION WOULD SEVERELY LIMIT
A WIDESPREAD FLASH FLOOD THREAT.

FOR FRIDAY...THE PACIFIC TROUGH WILL CLOSE OFF AND SHIFT TO THE
CENTRAL CALIFORNIA COAST. GUIDANCE...NOW INCLUDING THE LATEST
NAM...PUSHES DRY AIR INTO MUCH OF THE FORECAST AREA. HAVE REDUCED
POPS FOR FRIDAY BUT STILL HOLD ON TO SLIGHT CHANCES OVER THE FAR
EASTERN PART OF THE FORECAST AREA JUST IN CASE THE MODELS FLIP.
HOWEVER...DID LEAVE THUNDERSTORM CHANCES ACROSS THE SIERRA DUE TO
THIS AREA BEING CLOSE TO THE FORCING OF THE UPPER LOW.

WITH THE UPPER LOW MOVING CLOSER...DECREASING THICKNESSES AND TEMPS
ALOFT...WE WILL SEE A COOLING TREND INTO THE WEEKEND. HIGH
TEMPERATURES BY FRIDAY SHOULD BE BACK TO NEAR NORMAL FOR THIS TIME
OF YEAR.

.LONG TERM...OVER THE WEEKEND...AN UPPER LOW MOVES FROM THE WEST
COAST NEAR POINT CONCEPTION SATURDAY MORNING TO NORTHEASTERN NEVADA
SUNDAY NIGHT. MODELS GENERATE MAINLY LIGHT PRECIPITATION OVER MUCH
OF THE FORECAST AREA AT SOME POINT OVER THE WEEKEND SO MOST AREAS
HAVE AT LEAST A SLIGHT CHANCE OF A SHOWER OR THUNDERSTORM. ALTHOUGH
THE LOW DOES NOT BRING A LOT OF MOISTURE WITH IT, MODELS AGREE IT
TAPS INTO A MOISTURE POOL OVER SOUTHERN ARIZONA AND WRAP SOME OF IT
NORTHWESTWARD INTO THE AREA. EVEN SO, WEATHER CONDITIONS FOR THE
MAJORITY OF TIME SHOULD BE MOSTLY SUNNY TO PARTLY CLOUDY DEPENDING
ON THE TIME OF DAY. TEMPERATURES OVER THE WEEKEND SHOULD BE NEAR OR
SLIGHTLY BELOW NORMAL WITH LOW PRESSURE OVER THE SOUTHWEST.

MONDAY THROUGH WEDNESDAY...

AS THE LOW MOVES AWAY FROM THE AREA MONDAY, PRECIPITATION SHOULD BE
PRETTY MUCH DONE. HOWEVER, I LEFT A SLIGHT CHANCE IN MOHAVE COUNTY
BASED ON THE ECMWF/GEM QPF FORECAST OF LIGHT PRECIP LINGERING THERE.
A WARMING TREND BEGINS MONDAY AND CONTINUES THROUGH AT LEAST MID
WEEK AS MODELS FORECAST STRENGTHENING SOUTHWEST FLOW ALOFT AS A
PACIFIC TROUGH APPROACHES. BY WEDNESDAY, TEMPERATURES ARE FORECAST
TO BE AROUND 5 DEGREES ABOVE NORMAL WITH SUNNY AND DRY WEATHER
EXPECTED. THE ONLY NOTABLE CHANGE TO THE INHERITED FORECAST WAS TO
INTRODUCE SOME SOUTHERLY WINDS WEDNESDAY AFTERNOON DUE TO THE
APPROACHING TROUGH. PREVIOUSLY, THE GFS WAS FORECASTING A RIDGE
STRENGTHENING OVER THE WEST BUT THE LATEST RUN FLIPPED TO MATCH THE
ECMWF/GEM AND GFS ENSEMBLE MEAN SOLUTIONS WHICH ALL FORECAST A
TROUGH MOVING INTO THE WEST.
&&

.AVIATION...FOR MCCARRAN...SOUTHEAST WINDS EARLY THIS AFTERNOON WILL
TRANSITION TO MORE OF A SOUTHERLY COMPONENT AROUND 02Z...THEN
SOUTHWEST AROUND 06Z. HOWEVER...THUNDERSTORMS IN THE AREA THIS
AFTERNOON CAN CAUSE PERIODS OF GUSTY ERRATIC WINDS. THUNDERSTORMS
ARE POSSIBLE ACROSS ALL CORRIDORS...BUT THE GREATEST COVERAGE CAN BE
EXPECTED IN THE PEACH SPRINGS AND MORMON MESA CORRIDORS.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...LIGHT WINDS WILL BECOME SOUTHERLY 10-15 KTS THROUGH
THIS EVENING BEFORE TRENDING NORMAL DIURNAL PATTERNS OVERNIGHT.
THUNDERSTORM COVERAGE WILL VARY FROM ISOLATED NORTH NEAR CENTRAL
NEVADA AND NORTHERN INYO COUNTY TO NUMEROUS OVER MOHAVE COUNTY.
&&

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

$$

SHORT TERM/AVIATION...PADDOCK
LONG TERM...SALMEN

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

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