Flash Flood in Arizona, September 14, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
230 PM PDT MON SEP 14 2015

.SYNOPSIS...SEVERAL DISTURBANCES WILL CROSS THE AREA THROUGH
WEDNESDAY AS A BROAD TROUGH OF LOW PRESSURE REMAINS IN PLACE ACROSS
THE REGION. THIS WILL RESULT IN SHOWERS AND THUNDERSTORMS AROUND
ALONG WITH GUSTY SOUTHWEST WINDS ESPECIALLY IN THE AFTERNOON AND
EVENING HOURS. DRY CONDITIONS ARE EXPECTED FROM THURSDAY THROUGH THE
WEEKEND. TEMPERATURES WILL REMAIN BELOW NORMAL THROUGH THURSDAY THEN
WARM BACK UP ON FRIDAY AND OVER THE WEEKEND. &&

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT.

SO FAR TODAY THE FORECAST HAS BEEN WORKING OUT ACCORDING TO PLAN.
STORMS THUS FAR HAVE BEEN FAIRLY ISOLATED WITH THE GREATEST ACTIVITY
OCCURRING ACROSS MOHAVE COUNTY AND RIGHT IN THE CENTER OF CLARK
COUNTY. A FEW ADDITIONAL SHOWERS AND STORMS MAY CONTINUE TO
REGENERATE ALONG THE TERRAIN AND DRIFT NORTHEAST INTO THE LAS VEGAS
VALLEY THROUGH THIS EVENING SO WILL MAINTAIN SLIGHT CHANCES.
COVERAGE SHOULD REMAIN FAIRLY ISOLATED AND DRYING HAS BEEN NOTED IN
THE SURFACE OBSERVATIONS IN THE PAST HOUR SO IM NOT PLANNING TO
ADJUST THE POPS UPWARDS DESPITE ONGOING STORMS.

WINDS ACROSS THE NEVADA TEST SITE HAVE BEEN CONSISTENTLY GUSTING
INTO THE 40 MPH OR HIGHER RANGE THIS AFTERNOON. WINDS ACROSS SAN
BERNARDINO COUNTY HAVE STRUGGLED TO REACH CRITERIA THUS FAR BUT HIGH
RES MODELS HINT AT A PEAK LATE THIS EVENING FOR WESTERN SAN
BERNARDINO SO WILL LET THAT RIDE. GREATEST UNCERTAINTY IS ACROSS
CLARK COUNTY. CLOUDS AND PRECIPITATION HAVE LIMITED SURFACE MIXING
POTENTIAL AND WINDS SO FAR HAVE NOT MATERIALIZED ALTHOUGH
SOUTHWESTERLY WINDS HAVE INCREASED AS OF THIS WRITING AND STRONGER
MIXING MAY ALLOW FOR STRONGER GUSTS YET THIS AFTERNOON. A DOWNSLOPE
WIND MAY DEVELOP LATE TONIGHT BUT IM NOT REAL CONFIDENT ON THIS AS
THE LOWER/MIDDLE ATMOSPHERE WILL BE MOISTENING IN ADVANCE OF SOME
TROPICAL REMNANTS MOVING IN FROM SOUTHERN CALIFORNIA. WIDESPREAD
CLOUDS AND SHOWERS TOMORROW MAY AGAIN LIMIT WIND POTENTIAL ACROSS
CLARK COUNTY.  RIGHT NOW THE BEST WINDOW FOR STRONG WINDS LOOKS TO
OCCUR AFTER THE WIND ADVISORY EXPIRES ON TUESDAY NIGHT INTO
WEDNESDAY. WITH ALL THE UNCERTAINTY I WILL LET THINGS RIDE BUT THE
NEED FOR A CONTINUED ADVISORY PRODUCT SHOULD BE EVALUATED FURTHER IN
THE FOLLOWING SHIFT.

TOMORROW...A SLUG OF REMNANT TROPICAL MOISTURE WILL MOVE INTO
SOUTHERN CALIFORNIA OVERNIGHT TONIGHT AND SHIFT EASTWARD INTO OUR
REGION TOMORROW. SHOWERS AND ISOLATED THUNDERSTORMS WILL LIKELY
BREAK OUT ALONG THE I-15 CORRIDOR IN THE MORNING HOURS AND EXPAND
EAST AND NORTHWARD THROUGH THE DAY. AS MENTIONED ABOVE...CLOUDS AND
SHOWER ACTIVITY MAY HAMPER SURFACE WINDS ACROSS CLARK COUNTY.
INSTABILITY LOOKS LIMITED TOMORROW BUT STILL ENOUGH WILL BE IN PLACE
TO SUPPORT ISOLATED TO SCATTERED THUNDERSTORMS.

DRIER AIR WILL PUSH IN ON WEDNESDAY LIMITING STORM CHANCES TO JUST
MOHAVE AND EASTERN LINCOLN COUNTY. GUSTY SOUTHWEST WINDS EXPECTED
ELSEWHERE WITH MUCH COOLER CONDITIONS EXPECTED THANKS TO BROAD
TROUGHING ACROSS THE WEST. TEMPERATURES WEDNESDAY AFTERNOON WILL
AVERAGE 5 TO 10 DEGREES BELOW NORMAL.

.LONG TERM...WEDNESDAY THROUGH MONDAY (FROM PREVIOUS DISCUSSION).

THE LONG TERM PERIOD BEGINS WITH AN AMPLIFIED SHORTWAVE TRAVERSING
THE SOUTHERN GREAT BASIN...SCOURING OUT MOISTURE FROM WEST TO EAST
ACROSS THE REGION. DEPENDING ON THE TIMING OF THE DRY AIR
INTRUSION...SUFFICIENT MOISTURE MAY REMAIN IN PLACE ACROSS FAR
EASTERN PORTIONS OF THE THE FORECAST AREA WEDNESDAY MORNING AND
AFTERNOON. THIS...COUPLED WITH JET DYNAMICS ASSOCIATED WITH THE LEFT
EXIT REGION OF THE JET COULD YIELD THUNDERSTORMS ACROSS EASTERN
LINCOLN...CLARK AND MOHAVE COUNTIES PRIOR TO MOISTURE GETTING
SCOURED OUT. OTHERWISE...EXPECT BREEZY AND GUSTY WINDS ACROSS MANY
LOCALES IN THE MOJAVE DESERT AND SOUTHERN GREAT BASIN. AT THIS
TIME...WIND STRENGTH APPEARS TO REMAIN BELOW ADVISORY CRITERIA
ACROSS MANY AREAS. HOWEVER...SOME AREAS...INCLUDING IN AND AROUND
THE SPRING MOUNTAINS...MAY NEED TO BE MONITORED CLOSER IN THE COMING
24-48 HOURS FOR HEADLINE CONSIDERATION.

THURSDAY...THE AFOREMENTIONED SHORTWAVE WILL HELP TO BREAK THE
STAGNANT LONGWAVE PATTERN OF TROF WEST/RIDGE EAST ACROSS THE U.S.
THIS WILL ALLOW THE SUBTROPICAL HIGH TO BEGIN SHIFTING WESTWARD
TOWARD THE DESERT SOUTHWEST ONCE AGAIN. THERE IS GOOD AGREEMENT
AMONG THE LATEST OPERATIONAL MODELS TONIGHT IN WEAK TROUGHING
KEEPING THE HIGH TO THE SOUTH AND EAST OF THE AREA THROUGH FRIDAY.
HOWEVER...BOTH THE 00Z GFS/ECMWF SOLUTIONS DEPICT A LOW DEVELOPING
OFF OF THE SOUTHERN CALIFORNIA COAST THIS WEEKEND...WHICH COULD SET
THE STAGE FOR MOISTURE TO GET FUNNELED UP BETWEEN THE LOW AND HIGH
INTO THE DESERT SOUTHWEST ONCE AGAIN BY THE END OF THE PERIOD.

TEMPERATURE-WISE...EXPECT AFTERNOON HIGHS TO GENERALLY RUN 4-6
DEGREES BELOW NORMAL WEDNESDAY AND THURSDAY BEFORE QUICKLY WARMING
BACK UP TO AVERAGE FRIDAY. TEMPERATURES WILL LIKELY RUN SEVERAL
DEGREES ABOVE AVERAGE NEXT WEEKEND AS THE SUBTROPICAL HIGH
REINTRODUCES RIDGING ALOFT TO THE FORECAST AREA.
&&

.AVIATION...FOR MCCARRAN...OUTSIDE OF OUTFLOW WINDS...WINDS ARE
EXPECTED TO FAVOR A SOUTH OR SOUTHWESTERLY DIRECTION THROUGH AT
LEAST WEDNESDAY. GUSTS DURING THE AFTERNOON HOURS WILL GENERALLY BE
IN THE 20-30 KT RANGE...WITH SPEEDS DECREASING TO AROUND 10 KTS
OVERNIGHT THROUGH MID-MORNING. SHRA OR PERHAPS A STRAY TS WILL BE
POSSIBLE BOTH THIS AFTERNOON AND AGAIN TUESDAY...WHICH COULD
GENERATE ERRATIC WIND SHIFTS. DRIER CONDITIONS ARE EXPECTED
WEDNESDAY. DOWNSLOPE WINDS OVER THE SPRING MOUNTAINS COULD CREATE
AREAS OF MECHANICAL TURBULENCE OVER THE EASTERN AND NORTHERN SLOPES
OF THE MOUNTAINS.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...DAYTIME WINDS FROM A SOUTH TO SOUTHWEST DIRECTION ARE
EXPECTED THROUGH WEDNESDAY ACROSS MUCH OF THE REGION. GUSTS OF 20-30
KTS ARE EXPECTED IN VALLEY LOCATIONS AND 30-40 KTS OVER THE HIGHER
TERRAIN. WINDS SHOULD DIMINISH SOMEWHAT DURING THE OVERNIGHT HOURS
IN MOST VALLEY LOCATIONS. STRONG RIDGETOP WINDS COULD CAUSE AREAS OF
MECHANICAL TURBULENCE OVER AND ESPECIALLY DOWNWIND OF HIGHER
TERRAIN. ISOLATED TO SCATTERED SHRA/TSRA WILL REMAIN POSSIBLE THIS
AFTERNOON AND AGAIN TUESDAY ACROSS PORTIONS OF THE REGION.
OCCASIONAL AREAS OF HZ AND FU ARE POSSIBLE IN AND NEAR KBIH DUE TO
FIRES IN THE REGION.

&&

.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...OUTLER
AVIATION...WOLCOTT
LONG TERM...PULLIN

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