Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 300449
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
949 PM PDT WED JUL 29 2015

.SYNOPSIS...
MONSOONAL MOISTURE AROUND STRONG HIGH PRESSURE OVER THE FOUR CORNERS
REGION WILL BRING WARM...HUMID WEATHER INTO THE REGION THROUGH
THURSDAY. SCATTERED SHOWERS AND THUNDERSTORMS ARE LIKELY OVER THE
MOUNTAINS AND DESERTS. SOME STORMS MAY DRIFT INTO THE INLAND VALLEYS
TONIGHT AND THURSDAY...AND POSSIBLY TO THE COAST AT TIMES. THE
AIRMASS DRIES OUT OVER THE WEEKEND INTO EARLY NEXT WEEK FOR LOWER
CHANCES FOR AFTERNOON THUNDERSTORMS OVER THE MOUNTAINS AND DESERTS.
THE MARINE LAYER WILL REMAIN MAINLY OVER THE COAST AND PORTIONS OF
THE VALLEYS.

&&

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

RADAR THIS EVENING SHOWS THAT THUNDERSTORM ACTIVITY HAS DIMINISHED
SUBSTANTIALLY OVER THE FORECAST AREA. HOWEVER...NOCTURNAL
THUNDERSTORM AND SHOWER ACTIVITY LOOKS POSSIBLE LATE TONIGHT THROUGH
THURSDAY MORNING AS AN EASTERLY WAVE MOVES OVER THE REGION. WITH THE
WAVE WILL ALSO BE A SECOND AND MORE SIGNIFICANT SURGE OF MOISTURE
INTO THE AREA...WITH NAM12 SHOWING PRECIPITABLE WATER INCREASING TO
2 INCHES. THE NAM12 AND GFS40 SHOW THIS WAVE WELL...AND THE GFS40
CONTINUES TO PAINT A LARGE AREA OF LIGHT PRECIPITATION OVER SOUTHERN
CALIFORNIA IN ASSOCIATION WITH THE WAVE. THE HRRR HAS BEEN FLIP-
FLOPPING WITH EACH RUN WITH HOW MUCH ACTIVITY OCCURS WITH THIS
WAVE...WITH SOME RUNS SHOWING SOME LIGHT SHOWERS MOVING THROUGH THE
REGION...AND OTHER RUNS SHOWING SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS ALL THE WAY TO THE COAST. HOWEVER...THERE IS A GOOD
AMOUNT OF ELEVATED INSTABILITY FROM THE COAST THROUGH THE DESERTS
INDICATED BY THE WRF AND GFS BUFKIT FORECAST SOUNDINGS FOR TONIGHT
INTO TOMORROW...SO IF THE VORT MAX ASSOCIATED WITH THE WAVE IS ABLE
TO TRIGGER ACTIVITY...IT SHOULD RESULT IN A FAIR AMOUNT OF LIGHTNING
AS WELL. THE STORMS SHOULD BE MOVING SOMEWHAT QUICKLY...AS THE 700-
500 MB FLOW IS FORECAST TO BE 15-30 KT OUT OF THE EAST.

THE WAVE LOOKS TO MOVE OFF TO THE WEST BY LATE THURSDAY
MORNING...AND THE CLEARER SKIES BEHIND IT SHOULD RESULT IN GOOD DAY-
TIME HEATING AND INSTABILITY FOR MOUNTAIN AND DESERT THUNDERSTORMS
TO DEVELOP. THE INLAND EMPIRE SHOULD HAVE A GOOD CHANCE OF SEEING
STORMS AS WELL...AS THE WRF SHOWS THE ELSINORE CONVERGENCE BOUNDARY
SETTING UP BY MID-AFTERNOON. THE 700-500 MB FLOW WILL BE A LITTLE
LIGHTER...BUT STILL 15-20 KT OUT OF THE SOUTHEAST...SO STORMS MAY
STILL MOVE AT A DECENT PACE. HOWEVER...WITH HOW HIGH THE MOISTURE
AND INSTABILITY WILL BE...EVEN BRIEF HEAVY RAINFALL MAY BE ENOUGH TO
PRODUCE FLASH FLOODING...ESPECIALLY OVER RECENT BURN SCARS. A FLASH
FLOOD WATCH GOES INTO EFFECT EARLY THURSDAY MORNING AND CONTINUES
THROUGH EARLY THURSDAY EVENING FOR THE MOUNTAINS...DESERTS AND
INLAND EMPIRE. SOME STORMS COULD MAKE IT ALL THE WAY TO THE COAST AS
WELL...ALTHOUGH THE BETTER CHANCES FOR THAT WILL BE WITH THE
AFOREMENTIONED EASTERLY WAVE MOVING THROUGH LATE TONIGHT INTO
THURSDAY MORNING.

THE REST OF THE FORECAST REMAINS ON TRACK.

THE LAST PART OF THE PREVIOUS DISCUSSION ISSUED AT 145 PM FOLLOWS...

ON THURSDAY NIGHT AND FRIDAY THE UPPER LEVEL WINDS SHIFT FROM THE
SOUTHEAST TO THE SOUTH AND MOST OF THE THUNDERSTORM ACTIVITY WILL BE
CONFINED TO THE MOUNTAINS AND DESERTS. OVER THE WEEKEND THE AIRMASS
DRIES OUT WITH PRECIPITABLE WATER LOWERING TO LESS THAN 1.00". THIS
WILL LOWER THE THUNDERSTORM THREAT OVER THE MOUNTAINS AND DESERTS
SATURDAY AND SUNDAY.

THE LONG RANGE PROGS KEEP THE SUBTROPICAL HIGH OVER THE SOUTHWEST
AND BRING IN A SMALL SURGE OF MONSOON MOISTURE BACK INTO SOUTHERN
CALIFORNIA FOR CONTINUED CHANCES OF AFTERNOON THUNDERSTORMS OVER THE
MTNS. LATE NEXT WEEK THE UPPER HIGH WILL BE SUPPRESSED SOUTHWARD BY
A TROUGH DEEPENING ALONG THE NORTHERN CALIFORNIA COAST. DRIER
SOUTHWEST FLOW WILL CURTAIL THUNDERSTORM DEVELOPMENT AS THE DEEPEST
MONSOON MOISTURE WILL BE FORCED SOUTH AND EAST OF OUR AREA.

MARINE LAYER CLOUDS CLUNG TO THE BEACHES THIS AFTERNOON AND A
SIMILAR OCCURRENCE IS POSSIBLE THURSDAY. A STRONG INVERSION WILL
REMAIN IN PLACE THROUGH FRIDAY WHICH MAY KEEP LOW CLOUDS AT THE
BEACHES INTO THE AFTERNOON.

&&

.AVIATION...
300315Z...COAST/VALLEYS...SCT CLOUDS ACROSS THE AREA FROM REMNANT
THUNDERSTORMS IN THE MOUNTAINS AND SOME REMNANT MARINE STRATUS ALONG
THE COAST WILL CONTINUE OVERNIGHT. THE BIGGER QUESTION IS WILL
NOCTURNAL THUNDERSTORMS OCCUR WITH THE WEAK UPPER LEVEL DISTURBANCE
OVER SOUTHEAST CA AND W AZ MOVING OVERHEAD? MODELS ARE LOOKING GOOD
FOR SOME DEVELOPMENT...BUT ONE RIGHT OVER A TERMINAL SITE IS THE
DIFFICULT QUESTION. IT IS LIKELY FLIGHT PATTERNS WILL NOTE SOME
CONVECTION SO VICINITY THUNDER IS IN THE FORECAST WITH GREATEST
CHANCES AFTER 300700Z TO AROUND 310200Z. MOST OF THIS WILL BE HIGH
BASES AT OR ABOVE 8000 FT MSL AND MOST OF THE AFTERNOON THUNDERSTORM
RISK...301900-310200Z... WILL BE MORE IN THE MOUNTAINS AND DESERT
WITH JUST REMNANT CLOUD ELEMENTS DRIFTING OVER THE AIRPORTS.

MTNS/DESERTS...THE SLIGHT CHANCE FOR SHOWERS AND THUNDERSTORMS WILL
CONTINUE THROUGH THE NIGHT UNTIL AROUND 301500Z. A BRIEF BREAK MAY
OCCUR BEFORE THINGS START REGENERATING WITH THE HEAT OF THE DAY FROM
301900-310200Z. THERE IS A RISK OF CB WITH TOPS TO 40000 FT MSL
OVERNIGHT AND AGAIN IN THE AFTERNOON AND EVENING ON THURSDAY. BASES
WILL GENERALLY BE AT OR ABOVE 8000 FT MSL EXCEPT LOWERING NEAR
THUNDERSTORMS.

&&

.MARINE...
8 PM...THERE IS A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS OVER
THE NEARBY COASTAL WATERS AND ESTUARIES OVERNIGHT THROUGH THURSDAY
AFTERNOON AS AN UPPER LEVEL DISTURBANCE MOVES OVER THE AREA.
OTHERWISE...NO HAZARDOUS MARINE WEATHER IS EXPECTED THROUGH SUNDAY.

&&

.BEACHES...
8 PM...ELEVATED SURF ON WEDNESDAY CAUSED A FEW PROBLEMS INCLUDING
STRONG RIP CURRENTS AT THE BEACHES OF SAN DIEGO COUNTY AND SOUTHERN
ORANGE COUNTY. THE SURF IS SUBSIDING THURSDAY...BUT THE RISK OF
LIGHTNING INCREASES OVERNIGHT THROUGH THURSDAY. LARGE RIP CURRENTS
ARE POSSIBLE AND LIGHTNING...THEREFORE THE BEACH HAZARD STATEMENT
WILL CONTINUE THROUGH THURSDAY EVENING. SURF CONDITIONS WILL IMPROVE
SLIGHTLY DURING THE DAY THURSDAY AS THE WELL 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. AGAIN...THE THUNDERSTORM POTENTIAL AND DANGEROUS CLOUD TO
BEACH/WATER LIGHTNING IS THERE OVERNIGHT TONIGHT INTO THURSDAY
EVENING.

&&

.SKYWARN...
SKYWARN ACTIVATION MAY BE REQUESTED ON THURSDAY.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...FLASH FLOOD WATCH FROM 3 AM PDT THURSDAY THROUGH THURSDAY
     EVENING FOR APPLE AND LUCERNE VALLEYS-COACHELLA VALLEY-
     RIVERSIDE COUNTY MOUNTAINS-SAN BERNARDINO COUNTY MOUNTAINS-
     SAN BERNARDINO AND RIVERSIDE COUNTY VALLEYS-THE INLAND
     EMPIRE-SAN DIEGO COUNTY DESERTS-SAN DIEGO COUNTY MOUNTAINS-
     SAN GORGONIO PASS NEAR BANNING.

     BEACH HAZARDS STATEMENT THROUGH THURSDAY EVENING FOR ORANGE
     COUNTY COASTAL AREAS-SAN DIEGO COUNTY COASTAL AREAS.

PZ...NONE.
&&

$$

PUBLIC...HARRISON
AVIATION/MARINE/BEACHES...PIERCE


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