Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 012025
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
125 PM PDT SUN MAY 1 2016

.SYNOPSIS...
LOW PRESSURE OVER THE SOUTHWESTERN STATES WILL WEAKEN...WITH A
WARMING TREND THROUGH TUESDAY. RESIDUAL MOISTURE AND INSTABILITY
WILL STILL SUPPORT SCATTERED SHOWERS...AND POSSIBLE THUNDERSTORM
DEVELOPMENT AFTERNOONS AND EVENINGS...NEAR THE MOUNTAINS. COOLER
WEDNESDAY AS ONSHORE FLOW BUILDS THE MARINE LAYER AHEAD OF AN
ONCOMING LOW PRESSURE CENTER LATE IN THE WEEK. THIS STORM SYSTEM
WILL BRING COOLER WEATHER...MORE CLOUDS....AND PERIODS OF SHOWERS
AND THUNDERSTORMS INTO THE WEEKEND.

&&

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

AT 1 PM PDT...MARINE CLOUDS COVERING COASTAL AREAS MUCH OF THE
MORNING HAD THINNED WHILE FARTHER INLAND...CLOUDS WERE BUILDING OVER
THE MTS. SHOWERS HAVE DEVELOPED ON RADAR OVER NORTHERN VENTURA
COUNTY. ONSHORE SURFACE PRESSURE GRADIENTS WERE WEAK...AND WINDS
GENERALLY LIGHT.

FOR THE REMAINDER OF TODAY...SHOWERS WILL BE DEVELOPING OVER THE MTS
WITH A CHANCE FOR ISOLATED THUNDERSTORMS. MOISTURE IS SUFFICIENT...
AND THE 18Z NAM HAS NEGATIVE LIFTED INDEX VALUES OVER THE MTS. MOST
OF THE HI RES MODELS GENERATE SPOTTY PRECIP THERE AS WELL LATER IN
THE DAY. BRIEF HEAVY RAIN IS POSSIBLE BASED ON PW OF OVER 3/4 INCH.

LINGERING MOISTURE IN THE LOW LEVELS AND CYCLONIC FLOW ALOFT WILL
KEEP SOME LOWER CLOUDS ALONG AND WEST OF THE MTS THROUGH MONDAY.
SLIGHTLY WARMER ON MONDAY AS HEIGHTS SLOWLY RISE. THERE IS ONE LAST
SHORTWAVE THAT IS FORECAST TO SLIP OVER AND EAST OF THE AREA...
ACCOMPANIED BY INCREASING WESTERLY FLOW ALOFT. LINGERING INSTABILITY
WILL CONTINUE A THREAT OF ISOLATED SHOWER DEVELOPMENT OVER THE MTS...
AND THE INCREASING WESTERLY FLOW ALOFT WILL STEER ANY THAT MANAGE TO
FORM ONTO THE DESERT SLOPES LATE IN THE DAY.

WEDNESDAY WILL BE A TRANSITION DAY AS ONSHORE FLOW INCREASES AHEAD
OF A DEEPENING LONGWAVE TROUGH OVER THE FAR EASTPAC. COOLER MOST
AREAS...BUT FAIR AFTER MORNING MARINE CLOUDS AND FOG DISSIPATE.

MODEL SOLUTIONS CONTINUE TO COALESCE AROUND THE ARRIVAL OF A CUT-OFF
LOW PRESSURE CENTER LATE IN THE WEEK. THE LATEST GUIDANCE SHOWS A
DEEPENING LONGWAVE TROUGH JUST OFFSHORE OF THE WEST COAST ON WED. A
CUT-OFF DEVELOPS OFF THE NOCAL COAST THU MORNING AND SLOWLY CHURNS
SOUTH ALONG THE CA COAST THROUGH FRI...MOVING INLAND OVER SOCAL ON
SAT...ACCOMPANIED BY SHOWERS AND ISOLATED THUNDERSTORMS. WESTERLY
WINDS WILL BE INCREASING AS EARLY AS WED OVER THE MTS/DESERTS...
LIKELY PEAKING ON THU. A FEW SHOWERS COULD BREAK OUT ON THU...BUT THE
HIGHER PROBABILITY FOR WIDESPREAD SHOWERS WILL COME ON THU NIGHT/FRI
MORNING.

CONFIDENCE IS HIGH FOR THE DEVELOPMENT OF THIS SYSTEM...BUT
SIGNIFICANT DIFFERENCES REMAIN WITH THE EVOLUTION THROUGH MON. THE
ECMWF MODEL DOES NOT EJECT THE SYSTEM COMPLETELY UNTIL SUN NIGHT...
WHILE THE 12Z GFS SENDS IT PACKING SAT NIGHT WITH ONLY SOME
RESIDUAL WRAP AROUND MOISTURE INTO THE MTS FOR SUN. CHANCE POPS ARE
IN THE FORECAST TO COVER THIS PERIOD FOR NOW...AND GIVEN THE DYNAMICS
AND COLD AIR...A FEW THUNDERSTORMS ARE LIKELY TO POP UP AS WELL.

LOOK FOR DRY AND MUCH WARMER WEATHER NEXT WEEK AS THE GUIDANCE
INDICATES RIDGE BUILDING OVER CA.

&&

.AVIATION...
012000Z...COAST/VALLEYS...SCT-BKN CLOUD LAYERS BETWEEN 3000-4000 FT
MSL THIS AFTERNOON. BKN-OVC CIGS WILL FILL BACK IN THIS EVENING,
GENERALLY MORE EXTENSIVE IN COVERAGE, WITH BASES 1500-2500 FT MSL.
LOW CLOUDS SCATTERING OUT BETWEEN 16-18Z MONDAY MORNING.

MOUNTAINS/DESERTS...SCT-BKN CLOUDS OVER AND NEAR THE MOUNTAINS WITH
BASES 8000-12000 FT MSL, CHANCE OF AFTERNOON SHOWERS OR AN ISOLATED
THUNDERSTORM OVER THE MOUNTAINS AND HIGH DESERT AND LESS WINDY
OVERALL.

&&

.MARINE...
100 PM...THROUGH WEDNESDAY...LIGHT WINDS EACH NIGHT AND MORNING,
FOLLOWED BY ONSHORE NORTHWEST WINDS 10-15 KT EACH AFTERNOON. FOR
THURSDAY AND FRIDAY, A DEEP PACIFIC TROUGH WILL BRING STRONGER AND
MORE CONSISTENT NORTHWEST WINDS AND A CHANCE OF RAIN.

&&

.BEACHES...
100 PM...A LONG-PERIOD SOUTHERLY SWELL WILL BRING ELEVATED SURF TO
SOUTHWEST FACING BEACHES TODAY AND MONDAY WITH STRONG RIP AND
LONGSHORE CURRENTS. A BEACH HAZARDS STATEMENT IS IN EFFECT THROUGH 9
PM THIS EVENING. SEE LAXCFWSGX FOR DETAILS.

&&

.SKYWARN...
SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE
ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.

&&

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

PZ...NONE.
&&

$$

PUBLIC...JAD
AVIATION/MARINE/BEACHES...TS


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