Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 201041
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
340 AM 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 TODAY 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.
&&

.SHORT TERM...THROUGH SUNDAY NIGHT...SATELLITE LOOPS SHOWED MID
LEVEL CLOUD COVER PROGRESSIVELY INCREASING ACROSS NORTHWEST ARIZONA
AND SOUTHEAST NEVADA. THIS WAS DUE TO THE CYCLONIC FLOW AROUND THE
CLOSED CENTERED NEAR THE SOUTHERN CALIFORNIA COAST BEGINNING TO PULL
MOISTURE OVER ARIZONA TOWARD THE NORTHWEST. MOISTURE CONTENT IS
QUITE HIGH OVER SOUTHERN ARIZONA WITH PWAT VALUES GENERALLY
1.25-1.75 INCHES. THIS MOISTURE WILL CONTINUE TO ADVECT ACROSS
NORTHWEST ARIZONA AND SOUTHERN NEVADA TODAY AND TONIGHT AND INTERACT
WITH THE BROAD UPWARD FORCING OF THE CLOSED LOW WHICH WILL SLOWLY
LIFT TO THE NORTHEAST. ALL OPERATIONAL AND HIGH RES MODELS ARE IN
QUITE GOOD AGREEMENT AT DEPICTING WIDESPREAD QPF ACROSS ACROSS
CENTRAL NYE...LINCOLN AND MOHAVE COUNTIES WITH A GRADUAL DECREASE IN
COVERAGE DEPICTED ACROSS CLARK...EASTERN SAN BERNARDINO COUNTIES AND
ZONES FARTHER TO THE WEST AND SOUTH. LINCOLN AND MOHAVE COUNTIES
SHOULD SEE AVERAGE QPF AMOUNTS OF 0.25-0.50 INCHES WITH LOCALIZED
AMOUNTS OVER 1 INCH POSSIBLE. HOWEVER...INDIVIDUAL STORM MOVEMENT
SHOULD BE OVER 15-20 MPH OR HIGHER WHICH SHOULD DIMINISH WIDESPREAD
FLASH FLOOD THREAT. NO FLASH FLOOD WATCH PLANNED.

ISOLATED SHOWERS WILL GET STARTED THIS MORNING THEN SCATTERED TO
NUMEROUS SHOWERS AND THUNDERSTORMS WILL DEVELOP THIS AFTERNOON AND
PERSIST TONIGHT ACROSS THE AFOREMENTIONED FAVORED COUNTIES. AS THE
CLOSED LOW CONTINUES TO LIFT ACROSS CENTRAL AND NORTHEAST NEVADA
SUNDAY...DRIER AIR WILL LEAD TO DECREASING COVERAGE OF SHOWERS AND
THUNDERSTORMS FROM SOUTHWEST TO NORTHEAST SUNDAY AFTERNOON AND
EVENING.

TEMPERATURES WILL TREND DOWNWARD SEVERAL DEGREES WITH THE INCREASING
CLOUD COVER...SHOWERS AND HEIGHT FALLS ASSOCIATED WITH THE UPPER LOW.

.LONG TERM...MONDAY THROUGH SATURDAY...HIGH PRESSURE RIDGING WILL
BUILD BACK INTO THE SOUTHWESTERN STATES BEGINNING MONDAY AND
CONTINUING THROUGH MIDWEEK. THIS WILL RESULT IN WARMING TEMPERATURES
AND DRY CONDITIONS WITH AFTERNOON HIGHS AVERAGING BETWEEN 4 AND 8
DEGREES ABOVE NORMAL FOR LATE SEPTEMBER.  THINGS BEGIN TO CHANGE ON
THURSDAY AS A STRONG PACIFIC TROUGH BEGINS TO NUDGE INTO THE PACIFIC
NORTHWEST AND THE FLOW AMPLIFIES ACROSS THE CONUS.  THIS WILL LEAD
TO INCREASING SOUTHWESTERLY WINDS ACROSS MUCH OF THE FORECAST
AREA...WITH LOCALLY STRONG WINDS POSSIBLE ACROSS THE DOWNSLOPE
FAVORED TERRAIN OF THE SIERRA AND OWENS VALLEY WHERE GUSTS COULD
EXCEED 40 MPH AT TIMES.

FRIDAY AND BEYOND...DETAILS RAPIDLY DIVERGE DURING THE LATTER
PORTION OF THE EXTENDED FORECAST DEPENDING ON WHICH FORECAST MODEL
YOU CHOOSE. THE LATEST ECMWF GUIDANCE DEVELOPS THE PAC NW TROUGHING
INTO A SHARPLY AMPLIFIED WEST COAST TROUGH THAT EVENTUALLY CLOSES
OFF OVER NORTHERN CALIFORNIA AND MEANDERS OVER THE NORTHERN GREAT
BASIN INTO EARLY NEXT WEEK...AN UNSETTLED PATTERN TO SAY THE LEAST.
THE GFS GUIDANCE IS MUCH MORE PROGRESSIVE WITH THE TROUGH AND
PUSHES THE TROUGH AXIS EAST OF OUR FORECAST AREA BY SATURDAY
AFTERNOON.  MEANWHILE MANY OF THE GFS ENSEMBLE MEMBERS DEVELOP THE
TROUGH IN SOME MANNER IN BETWEEN, WITH MANY KEEPING A CLOSED LOW
SOMEWHERE OVER SOUTHERN CALIFORNIA.  GIVEN THE UNCERTAINTY...DIDN`T
MAKE ANY MAJOR CHANGES TO THE PRECIPITATION CHANCES BUT CONTINUED TO
TREND TEMPERATURES COOLER FOR THE WEEKEND.
&&

.AVIATION...FOR MCCARRAN...MOISTURE WILL INCREASE TODAY LEADING TO
SCATTERED SHOWERS AND THUNDERSTORMS OVER SOUTHERN NEVADA THIS
AFTERNOON THROUGH TONIGHT. PREVAILING WINDS WILL BE SOUTHEAST AROUND
5-8 KTS LATE THIS MORNING AND AFTERNOON BUT GUSTY AND ERRATIC WINDS
CAN BE EXPECTED LATE THIS AFTERNOON AND EVENING DUE TO SHOWERS AND
THUNDERSTORMS NEAR THE TERMINAL AREA. STORM COVERAGE WILL BE MOST
EXTENSIVE IN 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 WILL INCREASE TODAY OVER MUCH OF SOUTHERN
NEVADA AND NORTHWEST ARIZONA WITH TO SCATTERED TO NUMEROUS SHOWERS
AND THUNDERSTORMS THIS AFTERNOON THROUGH TONIGHT. LOWERING CLOUDS
BASES WILL LEAD TO MARGINAL VFR CONDITIONS OVER SOUTH CENTRAL NEVADA
AND NORTHWEST ARIZONA WITH MOUNTAIN OBSCURMENT LIKELY. A CLEARING
TREND WILL OCCUR FROM SOUTHWEST TO NORTHEAST SUNDAY.
&&

.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.
&&

$$

SHORT TERM/AVIATION...ADAIR
LONG TERM...OUTLER

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