Area Forecast Discussion
Issued by NWS Las Vegas, NV

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000
FXUS65 KVEF 150348
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
848 PM PDT SUN SEP 14 2014

.SYNOPSIS...

ISOLATED THUNDERSTORMS ARE POSSIBLE MONDAY MAINLY OVER AREAS SOUTH
AND EAST OF LAS VEGAS. CLOUDS WILL INCREASE TUESDAY WITH A GREATER
CHANCE OF THUNDERSTORMS ACROSS MOHAVE AND SAN BERNARDINO COUNTIES AS
MONSOON MOISTURE SURGES NORTHWARD UNDER THE INFLUENCE OF HURRICANE
ODILE.
&&

.UPDATE...
THE FEW THUNDERSTORMS WE HAD DEVELOP TODAY HAVE DISSIPATED WITH LOSS
OF HEATING...YET WE STILL HAVE SOME DEBRIS CLOUDS OUT THERE. THESE
OBSERVATIONS AND LATEST MODEL TRENDS ARE COVERED WELL IN THE CURRENT
FORECAST. NO IMMEDIATE UPDATES NEEDED TONIGHT.
&&

.PREVIOUS DISCUSSION...
233 PM PDT SUN SEP 14 2014

.SHORT TERM...TONIGHT THROUGH TUESDAY NIGHT...

MONSOONAL MOISTURE HAS INCREASED SLIGHTLY ACROSS THE AREA WITH WITH
PRECIPITABLE WATER VALUES A LITTLE ABOVE NORMAL. WITH SOME
INSTABILITY IN PLACE...A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE
MONDAY. HOWEVER...HIGH PRESSURE AND LACK OF DYNAMIC FORCING SHOULD
KEEP STORMS ISOLATED...INITIATING MAINLY OVER THE MOUNTAINS OF
MOHAVE COUNTY AND PORTIONS OF SAN BERNARDINO COUNTY. THE FIRST
INFLUENCE OF HURRICANE ODILE WILL BE SEEN AS A SURGE OF MOISTURE
HEADS INTO THE AREA BRINGING AN INCREASE IN CLOUDS FOR TUESDAY.
THIS ADDITIONAL MOISTURE WILL BRING AN INCREASE IN THUNDERSTORMS
ACROSS THE SOUTHEASTERN HALF OF THE CWA INCLUDING MOHAVE...EASTERN
AND SOUTHERN SAN BERNARDINO AND SOUTHERN CLARK COUNTY.  STORMS MAY
CONTINUE INTO TUESDAY NIGHT IN THESE AREAS.

.LONG TERM...WEDNESDAY THROUGH SUNDAY...WET AND UNCERTAIN. THOSE ARE
THE BEST TWO WORDS TO DESCRIBE THE LONG TERM PERIOD THIS AFTERNOON.

THE SETUP...THE TWO MAIN PLAYERS THROUGH THE LONG TERM PERIOD WILL
BE WHAT EVER REMAINS OF HURRICANE ODILE [PRONOUNCED OH-DEAL] AND A
DIGGING THROUGH/CUTOFF LOW ALONG OR OVER THE WEST COAST. THESE TWO
FEATURES BY THEMSELVES ARE OFTEN NOT WELL RESOLVED AT LONG LEAD
TIMES...LET ALONE THE INTERACTION BETWEEN THEM. AT THE MOMENT...
MEDIUM RANGE MODELS ARE STILL STRUGGLING TO COME TO A CONSENSUS ON
HOW TO HANDLE THE TROUGH/CUTOFF LOW. THE GENERAL TREND OVER THE PAST
COUPLE DAYS HAS BEEN TOWARDS DEVELOPING A CUTOFF LOW SOMEWHERE
BETWEEN LAS VEGAS AND A WAYS OFF THE CALIFORNIA COAST. WHERE THIS
FEATURE ULTIMATELY ENDS UP WILL PLAY A VITAL ROLE IN THE WEATHER
FROM LATE THURSDAY ONWARD. ONE OTHER ITEM OF NOTE IS THE COMPARISON
OF THIS SETUP WITH THAT OF NORBERT LAST WEEK. WHILE THERE ARE SOME
SIGNIFICANT SIMILARITIES BETWEEN THE TRACK OF ODILE AND NORBERT
THERE ARE ALSO SIGNIFICANT DIFFERENCES. ONE...OVERALL THERE APPEARS
TO BE SLIGHTLY [EMPHASIS ON SLIGHTLY] LESS MOISTURE PUSHED ACROSS
THE REGION WITH THIS SETUP. TWO...IF THE CUTOFF LOW SOLUTION PANS
OUT...THE DYNAMICS OF THIS SYSTEM MAY BE QUITE DIFFERENT. SO WHILE
IT IS LIKELY THAT WE WILL HAVE SIGNIFICANT RAINFALL AND THE
POTENTIAL FOR FLASH FLOODING IN PORTIONS OF THE AREA...WE CANNOT
STRESS ENOUGH THAT IT IS UNLIKELY THAT THE IMPACTS WILL BE EXACTLY
THE SAME.

BACKING UP A STEP TO WEDNESDAY AND THURSDAY...MODELS ARE IN FAIRLY
GOOD AGREEMENT THAT MOISTURE WILL BE SURGING NORTH INTO THE FORECAST
AREA TUESDAY NIGHT THROUGH WEDNESDAY. THE BEST ADVECTION CORE WILL
BE TAKING PLACE ALONG OR JUST WEST OF THE COLORADO RIVER VALLEY ALL
THE WAY UP INTO CENTRAL NEVADA BY LATE WEDNESDAY. AS RESULT
PRECIPITATION CHANCES WILL ALSO SPREAD NORTH THROUGH THE DAY. 24
HOURS AGO...MOST GUIDANCE INDICATED AN EMBEDDED VORTICITY LOBE BEING
EJECTED NORTH ACROSS THE FORECAST AREA LATE WEDNESDAY INTO THURSDAY.
WHILE THAT FEATURE IS STILL EVIDENT IN THE LATEST GUIDANCE IT WEAKER
AN GETS PUSHED OFF TO THE EAST MUCH MORE RAPIDLY THAN BEFORE [EAST
OF THE AREA BY MID DAY THURSDAY]. INSTEAD WITH THE POTENTIAL CUTOFF
LOW FORMING ALONG THE CALIFORNIA COAST BY THURSDAY AFTERNOON THERE
COULD BE A FAIRLY GOOD AREA OF UPPER LEVEL DIVERGENCE [LIFT] OVER
PORTIONS OF THE AREA. BASED ON THE AVERAGE OF THE CURRENT GFS AND
ECMWF RUNS THIS AREA OF LIFT WOULD COINCIDE FAIRLY WELL WITH THE
SLUG OF TROPICAL MOISTURE OVER THE NORTHEASTERN HALF OF THE FORECAST
AREA [LINCOLN...CLARK... AND NORTHERN MOHAVE COUNTIES]. HOWEVER WITH
THE UNCERTAINTY IN THE LOW`S POSITION THIS COULD EASILY CHANGE.

AS WE MOVE INTO THURSDAY NIGHT AND ONWARD ANY CONFIDENCE THAT WE
HAVE FALLS APART PRETTY QUICKLY. THE BRUNT OF THE HIGH-GRADE
TROPICAL MOISTURE IS EXPECTED TO BE EXITING TO THE EAST BY 12Z
FRIDAY BUT ISOLATED TO SCATTERED STORMS WILL REMAIN POSSIBLE THROUGH
THE DAY. MODELS HAVE BEEN ALL OVER THE BOARD WITH RESPECT TO
PLACEMENT AND TIMING OF THE UPPER LEVEL LOW. THE LATEST RUNS OF THE
ECMWF...GFS...AND GEM ALL INDICATE SOME SORT OF CUTOFF LOW. THE GFS
[WHICH WAS ONE OF THE LATER MODELS TO COME TO THE CUTOFF IDEA] IS
THE FASTEST...MOVING THE LOW ACROSS THE AREA SATURDAY. THE 12Z ECMWF
[ADMITTEDLY MUCH FASTER THAN ITS 00Z COUSIN] IS THE SLOWEST...MOVING
THE LOW OVER THE GREAT BASIN SUNDAY. MEANWHILE THE GEM LIES
SOMEWHERE IN BETWEEN. WITH NO REAL CONSENSUS I FELT COMPELLED TO
LEAVE IN AT LEAST SLIGHT CHANCE POPS THROUGH SUNDAY. I EVEN LEFT IN
POPS ACROSS THE NORTHERN HALF OF THE AREA DURING THE OVERNIGHT HOURS
SINCE DYNAMICS ASSOCIATED WITH THE LOW COULD KEEP SHOWERS GOING AT
NIGHT.

&&

.AVIATION...FOR MCCARRAN...

EAST TO SOUTHEAST WIND WILL REMAIN THROUGH THE EVENING BECOMING
SOUTHERLY OVERNIGHT. WIND WILL BE MAINLY 5 TO 8 KT WITH BRIEF
PERIODS APPROACHING 10 KT. LIGHT AND VARIABLE WIND IS EXPECTED EARLY
MONDAY WITH A RETURN TO LIGHT EAST-SOUTHEAST WIND AROUND MIDDAY.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...

MAINLY LIGHT SOUTH TO SOUTHEAST WIND EXPECTED TONIGHT ACROSS MUCH OF
THE AREA.  ISOLATED THUNDERSTORMS ARE POSSIBLE NEAR THE HIGH TERRAIN
OF THE SIERRA AND MOHAVE COUNTY THROUGH THE EVENING. FOR
MONDAY...LIGHT AND VARIABLE WIND IS EXPECTED WITH SOUTHWEST WIND SUB
10 KT DEVELOPING ACROSS SAN BERNARDINO COUNTY.  AFTERNOON
THUNDERSTORMS ARE POSSIBLE.

&&

.SPOTTER INFORMATION STATEMENT...SPOTTER ACTIVATION IS NOT EXPECTED
THROUGH TUESDAY. HOWEVER SPOTTERS ARE ENCOURAGED TO REPORT ANY
SIGNIFICANT WEATHER ACCORDING TO STANDARD OPERATING PROCEDURES.

&&

$$

UPDATE..PADDOCK
PREVIOUS DISCUSSION...BERC/WOLCOTT

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