Flash Flooding and Flood in California, July 29 to 30, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
930 AM PDT WED JUL 29 2015

.SYNOPSIS...INCREASING MONSOON MOISTURE WILL BRING WARMER...MORE
HUMID WEATHER ALONG WITH SCATTERED THUNDERSTORMS TO THE REGION
THROUGH EARLY NEXT WEEK. MOST OF THE THUNDERSTORMS WILL BE OVER THE
MOUNTAINS AND DESERTS...BUT A FEW THUNDERSTORMS MAY DRIFT OVER THE
COASTAL AND VALLEY AREAS TODAY AND THURSDAY.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

THUNDERSTORMS RUMBLED ACROSS IMPERIAL COUNTY THIS MORNING COINCIDENT
WITH A SURGE OF DEEP MONSOON MOISTURE FROM THE SOUTHEAST.
PRECIPITABLE WATER ON THE 12Z YUMA SOUNDING WAS 1.91". AT MIRAMAR
THERE WAS AN IMPRESSIVE INCREASE IN PWAT THE PAST 12 HOURS FROM
0.69" AT 00Z TO 1.61" AT 12Z. MOST OF THE MOISTURE WAS ABOVE 700 MB
WITH A DRIER LAYER BELOW (INVERTED V PROFILE). THAT MEANS THERE WILL
BE A THREAT FOR GUSTY DOWNDRAFT WINDS WITH ANY THUNDERSTORMS THAT
DEVELOP TODAY. MUCAPE WAS 600 J/KG AND DAYTIME HEATING WILL BE THE
DRIVING FORCE BEHIND THE CONVECTION TODAY. STORMS WILL MOVE AT A
GOOD PACE TODAY WITH MID LEVEL WINDS ON BOTH SOUNDINGS SHOWING
SOUTHEAST WINDS OF 15-20KT. THIS WILL REDUCE THE FLASH FLOOD
POTENTIAL SOMEWHAT...BUT TRAINING ECHOES OVER THE SAME REGION WILL
BE A CONCERN. THE STRONG FLOW MAY PUSH STORMS WEST INTO THE INLAND
VALLEYS AND PERHAPS AS FAR AS THE COASTAL ZONES.

THE MARINE LAYER CLOUDS WERE RETREATING BACK TO THE COAST THIS
MORNING. THE MARINE LAYER WILL TURN A LITTLE SHALLOWER AS THE UPPER
HIGH STRENGTHENS...AND THE STRONG INVERSION WILL RESULT IN A SLOWER
BURNOFF AND MAY KEEP CLOUDS AT THE BEACHES INTO THE AFTERNOON THE
NEXT FEW DAYS.

CONVECTION MAY INTENSIFY THIS EVENING AND OVERNIGHT TONIGHT WHEN THE
EASTERLY WAVE OVER SOUTHWEST ARIZONA THIS MORNING MOVES NORTHWEST
ACROSS SO-CAL. THE FLASH FLOOD THREAT WILL BE ELEVATED WITH THE
POTENTIAL FOR HEAVY RAINS WITH DEEP LAYER MOISTURE AND AN UPPER
LEVEL TRIGGER IN PLACE.

MORE DIURNALLY DRIVEN CONVECTION IS LIKELY THURSDAY WITH SLOWER
MOVING CELLS BRINING A HIGHER RISK FOR FLASH FLOODING.

ON THURSDAY NIGHT AND FRIDAY THE FLOW SHIFTS MORE SOUTHERLY AND WILL
REMAIN THAT WAY THROUGH THE WEEKEND. THAT WILL CONFINE MOST OF THE
THUNDERSTORMS TO THE MOUNTAINS AND DESERTS FRIDAY THROUGH SUNDAY.
ALSO...THE AIRMASS DRIES OUT SLIGHTLY FRIDAY AND SATURDAY WHEN THE
THUNDERSTORM COVERAGE OVER THE MOUNTAINS WILL NOT BE AS WIDESPREAD.

THE LONG RANGE PROGS KEEP THE SUBTROPICAL HIGH OVER THE SOUTHWEST
THROUGH THE MIDDLE OF NEXT WEEK. LATE NEXT WEEK THE HIGH GETS
SUPPRESSED SOUTHWARD BY A TROUGH DEEPENING ALONG THE NORTHERN
CALIFORNIA COAST. DRIER SOUTHWEST FLOW INTO SO-CAL WILL CURTAIL
THUNDERSTORM CHANCES AS THE DEEPEST MONSOON MOISTURE WILL BE
FORCED SOUTH AND EAST OF OUR AREA.

&&

.AVIATION...

291530Z...COAST/VALLEYS...BKN-OVC STRATUS WITH BASES FROM 1400-1700
FEET MSL AND TOPS AROUND 1800-2200 FT MSL WILL LINGER OVER PORTIONS
OF THE COAST THROUGH 18Z. SCT CLOUDS AOA 10000 FT MSL AND LIGHT
WESTERLY SEA BREEZES WILL PREVAIL THIS AFTERNOON. AN ISOLATED SHOWER
OR THUNDERSTORM CAN NOT BE RULED OUT FOR THE 21Z-03Z PERIOD. BKN-OVC
LOW CLOUDS WILL SLOWLY RETURN TO THE COAST BETWEEN 04Z AND 08Z
THURSDAY WITH BASES IN THE 1300 TO 1600 FT MSL RANGE. THE POTENTIAL
FOR SHOWERS AND THUNDERSTORMS WILL INCREASE AFTER 03Z...WITH 06-12Z
BEING THE MOST PROBABLE TIME FOR IMPACTS AT THE COASTAL AND VALLEY
TAF SITES. LOW CLOUDS SHOULD CLEAR TO THE COAST BY 17Z
THURSDAY...WITH THE SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS
CONTINUING INTO THURSDAY EVENING...PARTICULARLY FOR KONT.

MTNS/DESERTS...SLIGHT CHANCE/CHANCE FOR SHOWERS AND THUNDERSTORMS
STARTING THIS MORNING AT 18Z AND CONTINUING THROUGH THE DAY ON
THURSDAY...WITH CB TOPS TO 40000 FT MSL. OTHERWISE...SCT CLOUDS AOA
8000 FT MSL AFTER 18Z AND CONTINUING INTO THE DAY ON THURSDAY.

&&

.MARINE...

830 AM...THERE IS A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS OVER
THE COASTAL WATERS LATE AFTERNOON THROUGH THURSDAY AFTERNOON AS AN
UPPER LEVEL DISTURBANCE MOVES OVER THE AREA. OTHERWISE...NO
HAZARDOUS MARINE WEATHER IS EXPECTED THROUGH SUNDAY.

&&

.BEACHES...

830 AM...A 2-3 FT LONG PERIOD SOUTHERLY AT 15-16 SEC WILL CONTINUE
TO BRING ELEVATED SURF AND THE THREAT OF STRONG RIP CURRENTS TO THE
BEACHES OF SAN DIEGO COUNTY AND SOUTHERN ORANGE COUNTY THROUGH THE
DAY TODAY. LARGE AND POWERFUL RIP CURRENTS ARE POSSIBLE...THEREFORE
THE BEACH HAZARDS STATEMENT WILL CONTINUES THROUGH THIS EVENING.
CONDITIONS WILL IMPROVE SLIGHTLY DURING THE DAY ON THURSDAY AS THE
SWELL DECLINES TO AROUND 2 FT AT 14-15 SEC...BUT THE RIP CURRENT
RISK WILL REMAIN HIGH. THE SLOW DOWNWARD TREND IN THE SWELL WILL
CONTINUE FOR FRIDAY THROUGH THE WEEKEND.

THERE IS A SLIGHT CHANCE OF THUNDERSTORMS AT THE BEACHES BEGINNING
LATE THIS AFTERNOON AND CONTINUING THROUGH THE DAY ON THURSDAY. ANY
STORMS THAT FORM WILL PRODUCE DANGEROUS CLOUD TO BEACH/WATER
LIGHTNING.

&&

.SKYWARN...
SKYWARN ACTIVATION MAY BE REQUESTED FOR THIS AFTERNOON AND EVENING
DUE TO THE CHANCE FOR THUNDERSTORMS.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...BEACH HAZARDS STATEMENT THROUGH THIS EVENING FOR ORANGE COUNTY
     COASTAL AREAS-SAN DIEGO COUNTY COASTAL AREAS.

PZ...NONE.

&&

PUBLIC...MOEDE
AVIATION/MARINE...ALBRIGHT