Flash Flooding in California, September 8 to 9, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
250 PM PDT TUE SEP 8 2015

.SYNOPSIS...HIGH PRESSURE ALOFT WILL BUILD NORTHWEST AND BECOME
CENTERED OVER THE MOJAVE DESERT THROUGH SATURDAY RESULTING IN ABOVE
NORMAL TEMPERATURES. MOIST AND UNSTABLE AIR WILL RESULT IN THE
POTENTIAL FOR SHOWERS AND THUNDERSTORMS THROUGH THURSDAY MAINLY IN
THE AFTERNOON AND EVENING HOURS SOUTH OF INTERSTATE 40. THERE IS
POTENTIAL FOR ADDITIONAL MOISTURE TO PUSH NORTH ACROSS THE REGION
SUNDAY AND MONDAY BRINGING A CHANCE OF SHOWERS AND THUNDERSTORMS
AREA WIDE &&

.SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT.

SHOWERS AND THUNDERSTORMS FORMED ABOUT WHERE EXPECTED THIS AFTERNOON
ACROSS MOHAVE...SOUTHERN CLARK AND EASTERN SAN BERNARDINO COUNTIES.
THIS ACTIVITY WILL CONTINUE INTO THE EVENING HOURS AND SHOULD
GENERALLY DIMINISH BY LATE EVENING. THE MODELS INDICATE A WEAK VORT
MAX MOVING NORTH JUST WEST OF RIVERSIDE COUNTY LATE TONIGHT WHICH
COULD TRIGGER A SHOWER OR THUNDERSTORM FROM TWENTY NINE PALMS TO THE
MOJAVE PRESERVE WHERE THE MODELS INDICATE LINGERING INSTABILITY
OVERNIGHT. I LEFT THE INHERITED SLIGHT CHANCE POPS IN THAT AREA BUT
CONFIDENCE IS LOW IN THE OCCURRENCE OF ANYTHING. MOISTURE AND
INSTABILITY WILL LINGER OVER SAN BERNARDINO AND SOUTHERN PORTIONS OF
CLARK AND MOHAVE COUNTIES WEDNESDAY THROUGH THURSDAY AS HIGH
PRESSURE MIGRATES NORTHWEST INTO THE AREA. THIS WILL KEEP A CHANCE
OF MAINLY AFTERNOON AND EVENING THUNDERSTORMS IN THESE AREAS. BY
FRIDAY THE HIGH WILL BE CENTERED RIGHT OVER THE FORECAST AREA WHICH
SHOULD AID IN SUPPRESSING THUNDERSTORM ACTIVITY AND RESULT IN MUCH
ABOVE NORMAL TEMPERATURES.

.LONG TERM...SATURDAY THROUGH TUESDAY.

COMPLEX WEATHER FORECAST FOR THE EXTENDED PERIOD WITH CONSIDERABLE
UNCERTAINTY AT THE MOMENT. THIS MORNINGS MODEL RUNS HAVE TRENDED
TOWARDS A WETTER AND MORE UNSETTLED WEATHER PATTERN PRIMARILY FROM
SUNDAY ONWARD BUT THE DETAILS ARE QUITE DIFFERENT.  GUIDANCE HAS
ALSO SHIFTED THE TRAJECTORY OF HURRICANE LINDA SLIGHTLY FURTHER
EASTWARD...PARALLELING THE BAJA COAST LINE BEFORE GRADUALLY
WEAKENING AND DRIFTING SLOWLY WEST ON APPROACH OF THE SOUTHERN
CALIFORNIA COAST. THIS IS A SIMILAR TRAJECTORY TO THE REMAINS OF
HURRICANE DOLORES IN JULY WHICH CAUSED PROBLEMS ACROSS MUCH OF THE
SOUTHWEST AND SOUTHERN CALIFORNIA. THE UPPER AIR PATTERN IS NOT AS
FAVORABLE TO DIRECT DEEP TROPICAL MOISTURE INTO THE REGION AS IT WAS
IN JULY BUT SOME INFLUENCE FROM THE TROPICAL SYSTEM IS LOOKING MORE
LIKELY.

WARM TEMPERATURES ARE STILL EXPECTED SATURDAY WITH HIGH TEMPERATURES
FIVE TO TEN DEGREES ABOVE NORMAL.  OUR SOUTHERN ZONES SOUTH OF
INTERSTATE 40 WILL REMAIN ON THE EDGE OF A DEEPER MOISTURE FIELD
WITH PRECIPITABLE WATER VALUES EXCEEDING 1.25 INCHES. WHILE COVERAGE
WILL BE SPARSE WITH THE LACK OF A TRIGGERING MECHANISM...CANT RULE
OUT SOME ISOLATED TERRAIN DRIVEN CONVECTION IN THESE AREAS AND I
HAVE ADDED IN SOME LOW POPS TO THE HIGHER TERRAIN IN THESE AREAS.

THINGS GET INTERESTING SUNDAY ONWARD AND GIVEN THE VARIOUS POSSIBLE
OUTCOMES AND LACK OF AGREEMENT OR CONSISTENCY I WILL ATTEMPT TO KEEP
THINGS BRIEF. THE 12Z GFS WANTS TO BRING THE REMNANT UPPER LEVEL
CIRCULATION OF LINDA EASTWARD AND DRAG IT ACROSS THE SOUTHWEST
SUNDAY INTO MONDAY BEFORE IT PHASES WITH A LARGE AND DEEP UPPER
LEVEL TROUGH WHICH QUICKLY BECOMES CARVED OUT ACROSS THE WEST
TUESDAY. THIS WOULD LEAD TO COOLER, WETTER, AND CLOUDIER CONDITIONS
BEFORE BECOMING MUCH COOLER AND WINDIER WITH THE ARRIVAL OF THE
FIRST STRONG FALL TROUGH. THE ECMWF SOLUTION IS MUCH MORE TAME BUT
STILL DEVELOPS A WEAK WEST COAST TROUGH WHICH INTERACTS WITH THE
REMAINS OF LINDA AND DIRECTS INTO OUR FORECAST AREA SUNDAY ONWARD.

WITH THE DETAILS STILL COMING TOGETHER...JUST TRENDED THE FORECAST
TOWARDS THE COOLER AND WETTER SIDE WHILE MAINTAINING A CONSERVATIVE
APPROACH. I BOOSTED POPS INTO THE SLIGHT CHANCE CATEGORY FOR MUCH OF
THE REGION SUNDAY THROUGH TUESDAY AND TEMPERED TEMPERATURES CLOSER
TO SEASONAL NORMALS. THIS FORECAST PERIOD IS SUBJECT TO CHANGE AS
DETAILS ARE FINE TUNED.
&&

.AVIATION...FOR MCCARRAN...WINDS WILL FAVOR TYPICAL DIURNAL TRENDS
THROUGH WEDNESDAY WITH GENERALLY EASTERLY WINDS DURING THE DAY AND
SOUTH/SOUTHWEST AT NIGHT. WIND SPEEDS SHOULD MAINLY REMAIN BELOW 8
KNOTS. SOME HIGH BASED CUMULUS CLOUDS WILL BE AROUND BUT
THUNDERSTORMS ARE EXPECTED TO REMAIN SOUTH OF THE LAS VEGAS VALLEY.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...WINDS WILL MAINLY FAVOR TYPICAL DIURNAL TRENDS THROUGH
WEDNESDAY. ISOLATED SHRA/TSRA ARE POSSIBLE THROUGH THIS EVENING AND
AGAIN WEDNESDAY AFTERNOON MAINLY ALONG AND SOUTH OF A LINE FROM
ROUGHLY KDAG-KIFP-KIGM. GUSTY AND ERRATIC WINDS ARE POSSIBLE IN AND
NEAR ANY SHRA/TSRA. SCT-BKN CLOUDS AOA 7K-12K FEET AS WELL ALONG AND
SOUTH OF A LINE FROM KDAG-KHND-KIGM. AREAS OF FU AND HZ ARE POSSIBLE
IN AROUND KBIH REDUCING VSBY AND CREATING LOCAL MOUNTAIN
OBSCURATIONS.
&&

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

SHORT TERM/AVIATION...HARRISON
LONG TERM...OUTLER

FOR MORE FORECAST INFORMATION...SEE US ON OUR WEBPAGE:

HTTP://WEATHER.GOV/LASVEGAS OR FOLLOW US ON FACEBOOK AND TWITTER

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LAS VEGAS NV
530 PM PDT TUE SEP 8 2015

...TIME...  ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
...DATE...  ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0500 PM     HEAVY RAIN       2 WSW LANDERS           34.25N 116.43W
09/08/2015  U0.00 INCH       SAN BERNARDINO     CA   TRAINED SPOTTER

            TRAINED SPOTTER REPORTED 2-3 INCHES OF WATER
            RUNNING OVER HANDLEY ROAD

&&

CFS