Area Forecast Discussion
Issued by NWS Las Vegas, NV

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000
FXUS65 KVEF 310456 CCA
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
955 PM PDT THU JUL 30 2015

.SYNOPSIS...THE COMBINATION OF DISTURBANCES MOVING NORTHWARD ACROSS
CENTRAL CALIFORNIA AND CENTRAL ARIZONA ALONG WITH SUFFICIENT
MOISTURE WILL RESULT IN SHOWERS AND THUNDERSTORMS THIS EVENING
MAINLY SOUTH AND WEST OF LAS VEGAS. LOCALLY HEAVY RAIN IS POSSIBLE
WHICH COULD RESULT IN FLASH FLOODING. LINGERING MOISTURE WILL RESULT
IN THE POTENTIAL FOR SHOWERS AND THUNDERSTORMS ACROSS PARTS OF THE
AREA THROUGH MONDAY. BY TUESDAY, DRIER AIR SHOULD WORK ON IN ENDING
THE CHANCE OF SHOWERS AND THUNDERSTORMS IN MOST AREAS.
&&

.UPDATE...WE ARE STILL WATCHING A FEW AREAS OF SHOWERS AND
THUNDERSTORMS ACROSS THE AREA THIS EVENING. THE MAIN AREAS EXTENDED
FROM SAN BERNARDINO AND SOUTHERN INYO COUNTY EAST TO THE COLORADO
RIVER VALLEY. OVERALL, ACTIVITY IS SHOWING A DOWNWARD TREND IN THIS
AREA WITH RESPECT TO HEAVY RAINFALL POTENTIAL AND THUS THE FLASH
FLOOD WATCH WAS ALLOWED TO EXPIRE. WE WILL ASSESS THE NEED OVERNIGHT
ON ANY FURTHER FLASH FLOOD WATCHES FOR UPCOMING PERIODS.

A FEW SHOWERS WERE ALSO EXITING NORTHWEST INYO COUNTY BUT SHOULD
THIS LOOKS TO BE DONE AND OVER WITH IN ANOTHER HOUR OR SO.

THE MOST INTENSE CONVECTION AS OF WRITING EXTENDS FROM NEAR THE
SOUTHERN END OF BADWATER TOWARD INDIAN SPRINGS. THIS ACTIVITY WAS
HEADING WEST. HOWEVER, LAPSE RATES OF -8C/KM AS WELL AS A NOTICEABLE
DRY-MOIST INTERFACE ON WATER VAPOR APPEAR TO BE ALLOWING CONVECTION
IN THIS AREA TO MAINTAIN A BIT MORE INTENSITY AND ALSO BE DECENT
RAIN PRODUCERS DESPITE THE FACT THAT THE 0.5 DEGREE KESX RADAR
REFLECTIVITY VALUES ARE ONLY AT BEST 40-45 DBZ. SOME OF THESE CELLS
COULD TRIGGER WIND GUSTS OVER 40 MPH.

WINDS WERE TWEAKED ACROSS THE AREA FOR THE REST OF THE NIGHT TO
ACCOUNT FOR DIRECTIONS AND LINGERING GUSTS FROM DECAYING SHOWER AND
THUNDERSTORM ACTIVITY. CLOUD COVER WAS ALSO ADJUSTED UP FOR TONIGHT
AS A LARGE BLOB OF CLOUDS WAS COVERING MUCH OF THE AREA AND WILL
TAKE TIME TO ERODE. SOME OF THIS CLOUD COVER WILL ALSO HEAD ON
NORTH.
&&

.AVIATION...FOR MCCARRAN...DECAYING SHRA/TSRA ACTIVITY EARLIER HAS
SENT OUTFLOW INTO THE LAS VEGAS VALLEY KEEPING WIND SPEEDS UP ABOVE
15 KTS. OVER THE NEXT HOUR SO, SPEEDS SHOULD DROP AND WINDS SHOULD
STAY MORE OF A TYPICAL NIGHTTIME SOUTHERLY DIRECTION AT 7-12 KTS.
WINDS ON FRIDAY 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. OVERALL CONFIDENCE IS LOW FOR ACTIVITY AT KLAS SO THE TAF
WILL BE KEPT DRY. MAINLY BKN CIGS AOA 15K FEET OVERNIGHT WITH SCT-
BKN CLOUDS AOA 12K FEET ON FRIDAY.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...SHRA/TSRA WILL CONTINUE OVERNIGHT BUT GRADUALLY
DECREASE IN COVERAGE WITH ACTIVITY MAINLY FROM A LINE FROM KLAS TO
KHII ON WEST AND IN AROUND KBIH EARLY. ONCE AGAIN ON FRIDAY
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.
OTHERWISE EXPECT WINDS TO FAVOR TYPICAL DIURNAL DIRECTION AND SPEED
TRENDS WITH SCT-BKN CLOUDS AOA 8K-15K FEET.
&&

.PREVIOUS DISCUSSION...
ISSUED AT 230 PM PDT THU JUL 30 2015

.SHORT TERM...THROUGH SATURDAY NIGHT.

AGAIN MADE ONLY SOME MINOR TWEAKS TO THE FRIDAY/SATURDAY PERIODS AS
MODELS HAVE BEEN CONSISTENT ADVERTISING A DIURNAL CONVECTIVE PATTERN
WITH STORMS DEVELOPING OVER THE HIGHER TERRAIN AND SPREADING INTO
THE VALLEYS INTO THE EVENING HOURS.

.LONG TERM...SUNDAY THROUGH THURSDAY.

THE LATEST MODEL GUIDANCE CONTINUES TO INDICATE A LOW GRADE MONSOON
PATTERN THROUGH THE END OF THE PERIOD...WITH IT POTENTIALLY
BEGINNING FAIRLY ACTIVE WITH HIGHER SHOWER AND STORM CHANCES ACROSS
MAINLY THE NEVADA AND ARIZONA ZONES SUNDAY. THIS DEPENDS ON THE
TIMING AND TRAJECTORY OF AN UPPER LEVEL WAVE THAT BOTH THE 00Z GFS
AND ECMWF HAVE TRANSLATING THE AREA EARLY SUNDAY MORNING. KEPT POPS
IN THE 20 TO 30 RANGE FOR NOW TO COVER FOR THIS SCENARIO...WITH
FURTHER UPDATES EITHER WAY DEPENDING ON HOW CONSISTENT OR NOT
CONSISTENT FUTURE GUIDANCE IS IN HANDLING THIS POTENTIAL FEATURE.

MONDAY...DRIER SOUTHWEST FLOW IS EXPECTED TO BEGIN TO FILTER INTO
THE REGION AND SCOUR OUT SOME OF THE MOISTURE THAT IS IN
PLACE...PARTICULARLY IN THE CALIFORNIA ZONES. DESPITE THIS...THE 00Z
ECMWF DEPICTS ANOTHER MID/UPPER WAVE TRAVERSING THE AREA...YIELDING
SHOWER AND THUNDERSTORM CHANCES ACROSS THE NEVADA AND ARIZONA ZONES.
THIS...ALONG WITH THE FACT THAT MODEL GUIDANCE TENDS TO BE ON THE
AGGRESSIVE SIDE IN SCOURING OUT MOISTURE THIS TIME OF YEAR WAS TAKEN
INTO CONSIDERATION...AND MINIMUM CHANGES TO POPS WERE MADE FOR
MONDAY FOR THE TIME BEING. TUESDAY THROUGH WEDNESDAY...DRIER AIR IS
EXPECTED TO SPREAD ACROSS MUCH OF THE AREA...AS A SHORTWAVE FROM AN
UPPER LEVEL LOW OFF OF THE COAST OF BRITISH COLUMBIA SWEEPS ACROSS
THE GREAT BASIN. THERE ARE HINTS IN GUIDANCE OF LOW GRADE MOISTURE
MAKING A RETURN BY THURSDAY AS HIGH PRESSURE SHIFTS BACK TO THE WEST
AND PULLS MOISTURE NORTHWARD. TEMPERATURES WISE...GIVEN THE MOISTURE
THAT IS EXPECTED TO REMAIN IN PLACE...AFTERNOON HIGHS WILL RUN
AROUND SEASONAL NORMALS THROUGH THE PERIOD WITH THE WARMEST DAYS
LIKELY COMING ON MONDAY AND TUESDAY WITH DRIER SOUTHWEST FLOW
FILTERING THROUGH THE AREA.
&&

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

$$

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

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