Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 210405 AAA
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
905 PM PDT SAT SEP 20 2014

.SYNOPSIS...A LOW PRESSURE SYSTEM CIRCULATING NEAR THE SOUTHERN
CALIFORNIA COAST WILL PULL MOISTURE ACROSS SOUTHERN NEVADA AND
NORTHWEST ARIZONA THROUGH SUNDAY LEADING TO SCATTERED TO NUMEROUS
SHOWERS AND THUNDERSTORMS. THE SYSTEM WILL LIFT AWAY TO THE
NORTHEAST BY LATE SUNDAY FOLLOWED BY DRY CONDITIONS AND ABOVE NORMAL
TEMPERATURES THROUGH THE FIRST HALF OF NEXT WEEK.
&&

.UPDATE...UPPER LOW OVER CENTRAL CALIFORNIA THIS EVENING PLACING
MUCH OF THE AREA UNDER REGION OF DIFFLUENCE ALOFT. THERE HAVE BEEN
THREE DISTINCT LINES OF THUNDERSTORMS AFFECTING THE AREA SINCE
AFTERNOON. MOST INTENSE LINE AT THIS HOUR CONTINUES TO BE LINE
RUNNING NEAR/ALONG HIGHWAY 93 FROM IN LINCOLN COUNTY SOUTH INTO
NORTHEAST LAS VEGAS VALLEY. OTHER LINE OVER SOUTHWEST INYO COUNTY
AND THE ONE FROM NEAR TONOPAH SOUTH TO DEATH VALLEY NATL PARK HAVE
SHOWN SIGNS OF WEAKENING. WILL BE MONITORING SOME OUTFLOW BOUNDARIES
AROUND LAS VEGAS FOR ANY DEVELOPMENT AS WELL. LINCOLN COUNTY WILL
REMAIN UNDER THE GUN THE REST OF TONIGHT INTO SUNDAY WHILE
DRIER/MORE STABLE AIR PRESENTLY OVER SAN BERNARDINO COUNTY GRADUALLY
SPREADS NORTH. FORECAST LOOKS FINE THE REST OF TONIGHT/SUNDAY. NO
UPDATE.
&&

.AVIATION...FOR MCCARRAN...OUTFLOW BOUNDARIES WILL AFFECT THE LAS
VEGAS VALLEY THROUGH 05Z-06Z THIS EVENING WITH NORTH-NORTHEAST WINDS
...GUSTING AROUND 25 KTS AT TIMES. BY LATE EVENING AND OVERNIGHT
WINDS SHOULD RETURN TO THE TYPICAL SOUTH-SOUTHWEST AT LESS THAN 10
KTS. ISOLATED SHOWERS/THUNDERSTORMS COULD AFFECT VALLEY TERMINALS
INTO LATE EVENING. STORM COVERAGE WILL BE MOST EXTENSIVE IN
BEATTY...PEACH SPRINGS...AND MORMON MESA CORRIDORS. BKN-OVC CLOUDS
WILL GENERALLY HAVE BASES 8-10 KFT BUT WILL LIKELY LOWER TO AROUND 6
KFT NEAR ANY SHOWERS AND THUNDERSTORMS. A CLEARING TREND WILL OCCUR
SUNDAY.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...MOISTURE CONTINUES TO INCREASE OVER MUCH OF SOUTHERN
NEVADA AND NORTHWEST ARIZONA WITH SCATTERED TO NUMEROUS SHOWERS AND
THUNDERSTORMS EXPECTED THROUGH TONIGHT. LOWERING CLOUDS BASES WILL
LEAD TO MARGINAL VFR CONDITIONS OVER SOUTH CENTRAL NEVADA AND
NORTHWEST ARIZONA WITH MOUNTAIN OBSCUREMENT LIKELY. A CLEARING TREND
WILL OCCUR FROM SOUTHWEST TO NORTHEAST SUNDAY.
&&


.PREV DISCUSSION...
245 PM PDT SAT SEP 20 2014

.SHORT TERM /THROUGH MONDAY NIGHT/...
THE UPPER LOW WE HAVE BEEN WATCHING THE LAST FEW DAYS OVER THE
WESTERN CALIFORNIA COAST IS STARTING TO MOVE NORTHEAST AND WILL
CONTROL OUR WEATHER THROUGH SUNDAY. THIS WILL PROVIDE SHOWER AND
THUNDERSTORM CHANCES AS WELL AS COOLER TEMPERATURES. DRY CONDITIONS
AND A WARMING TREND WILL COMMENCE MONDAY.

MOISTURE CONTINUES TO INCREASE ACROSS OUR AREA...WRAPPING
CYCLONICALLY AROUND THE UPPER LOW TO OUR WEST. SCATTERED SHOWERS AND
THUNDERSTORMS HAVE BEEN AROUND THROUGHOUT THE DAY AND WILL INCREASE
IN COVERAGE THROUGH THIS EVENING. AREA PW VALUES RANGING FROM 1 INCH
IN OUR NORTHWEST TO 1.5 INCHES ALONG THE COLORADO RIVER NEAR NEEDLES
ARE FORECAST BY EARLY EVENING...WHICH WOULD PROMOTE HEAVY RAIN. AREA
AVERAGE RAIN AMOUNTS OF 0.25-0.50 INCHES WITH LOCALIZED AMOUNTS OVER
1 INCH WILL BE POSSIBLE. THE AVERAGE STORM MOTION WILL BE AROUND 20
MPH OR SO...WITH STORMS MOVING FROM SOUTHEAST TO NORTHWEST. THIS
MOTION WOULD GENERALLY LIMIT THE AMOUNT OF TIME ANY ONE CELL IS OVER
ONE PARTICULAR AREA. HOWEVER...THERE CAN BE SOME ISOLATED AREAS
WHERE REDEVELOPMENT OR TRAINING CONVECTION FOR A SHORT PERIOD OF
TIME MAY WARRANT THE ISSUANCE OF A FLASH FLOOD WARNING HERE AND
THERE. WITH WIDESPREAD FLASH FLOODING NOT ANTICIPATED AT THIS
TIME...WILL NOT ISSUE ANY WATCH PRODUCTS BUT TRENDS WILL BE
MONITORED. THE STRONGEST STORMS MAY ALSO PRODUCE SOME GUSTY WINDS IN
EXCESS OF 45 MPH AS WELL AS SOME HAIL. SO PLEASE KEEP ALERT OF
CHANGING WEATHER CONDITIONS THIS AFTERNOON AND EVENING PARTICULARLY
IF YOU HAVE OUTDOOR PLANS.

THE LOW WILL CONTINUE A NORTHEAST TRACK ACROSS CALIFORNIA AND NEVADA
TONIGHT AND SUNDAY. THE FOCUS FOR CONVECTION WILL SHIFT NORTH...WITH
DRIER AIR WORKING INTO OUR CALIFORNIA AREAS LATE TONIGHT AND
ESPECIALLY BY SUNDAY AFTERNOON. SO...SHOWER AND THUNDERSTORM CHANCES
WILL BE MAINLY CONFINED TO SOUTHERN NEVADA AND NORTHWEST ARIZONA
SUNDAY. THE LOW WILL EXIT THE REGION BY SUNDAY NIGHT WITH DRY AIR
PUSHING ACROSS THE REST OF THE AREA OVERNIGHT...BRINGING AN END TO
SHOWER AND STORM CHANCES.

.LONG TERM...TUESDAY AND WEDNESDAY. HIGH PRESSURE EXPANDS OVER THE
AREA IN RESPONSE TO A DEEPENING PACIFIC TROUGH OFF THE WEST COAST.
OVERALL, DRY AND MOSTLY CLEAR CONDITIONS ALONG WITH LIGHT WINDS ARE
EXPECTED. TEMPERATURES ARE FORECAST TO BE 4-8 DEGREES ABOVE NORMAL.

WEDNESDAY THROUGH SATURDAY...CONTINUED TRENDING THE FORECAST WITH
THE MORE CONSISTENT GFS DURING THIS PERIOD BUT DID NOT COMPLETELY
RULE OUT THE ECMWF GIVEN ITS AGREEMENT WITH THE GFS REGARDING A
CLOSED LOW MOVING OVER THE GREAT BASIN. THE GFS BRINGS A SHARP
SHORTWAVE AROUND THE BASE OF A PACIFIC TROUGH AND INTO NORTHERN AND
CENTRAL CALIFORNIA THURSDAY. THIS WOULD RESULT IN BREEZY TO LOCALLY
WINDY CONDITIONS ACROSS THE AREA WITH POSSIBLE WEAK DOWNSLOPE FLOW
OCCURRING ALONG THE EASTERN SIERRA SLOPES. THE GFS SOLUTION LIFTS
THE SHORTWAVE QUICKLY TO THE NORTHEAST WITH THE MAIN TROUGH AXIS
THEN PUSHING INTO CALIFORNIA AND NEVADA FRIDAY. IF THE GFS IS
CORRECT, THERE COULD BE A PERIOD OF STRONG WINDS ACROSS PORTIONS OF
THE AREA FRIDAY WITH WARM TEMPERATURES AGAIN OVER THE DESERTS BUT
COOLING CONDITIONS OVER INYO COUNTY AND THE SOUTHERN GREAT BASIN.
COOLER WEATHER WOULD THEN BE IN STORE FOR THE BEGINNING OF THE
WEEKEND WITH TEMPERATURES POTENTIALLY WELL BELOW NORMAL FOR LATE
SEPTEMBER. THE ECMWF IS MUCH WETTER THAN THE GFS ON SATURDAY DUE TO
THE LOCATION OF THE LOW SO THE OFFICIAL FORECAST TAKES THIS INTO
ACCOUNT WITH A SLIGHT CHANCE OF SHOWERS IN THE FAVORED REGIONS OF
THE LOW WHICH INCLUDES PORTIONS OF THE SIERRA, THE NORTHERN CWA AND
MOHAVE COUNTY.
&&

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME. HOWEVER....SPOTTERS
ARE ENCOURAGED TO REPORT ANY SIGNIFICANT WEATHER CONDITIONS
ACCORDING TO STANDARD OPERATING PROCEDURES.
&&

$$

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

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