Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 031544
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
844 AM PDT SUN MAY 3 2015

.SYNOPSIS...

A WEAK LOW PRESSURE SYSTEM OFF THE COAST OF SOUTHERN CALIFORNIA WILL
MOVE INLAND THROUGH MONDAY BRINGING ADDITIONAL CLOUDS...COOLING...
AND A CHANCE FOR LATE DAY SHOWERS OVER THE HIGHER MOUNTAINS. ONSHORE
FLOW WILL INCREASE THROUGH FRIDAY AS A COLDER LOW PRESSURE TROUGH
DIVES SOUTH OVER THE STATE. GUSTY WESTERLY WINDS WILL DEVELOP OVER
THE MOUNTAINS AND DESERTS...AND THE MARINE LAYER WILL DEEPEN
FURTHER...RESULTING IN MUCH BELOW AVERAGE DAYTIME TEMPERATURES...
AND A CHANCE OF SHOWERS MAINLY THURSDAY AND FRIDAY. DRY AND A LITTLE
WARMER BY NEXT WEEKEND AS THE TROUGH EXITS THE REGION.

&&

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

MARINE CLOUDS WERE EXTENSIVE W OF THE MTS THIS MORNING...BUT ABOVE
THE STRATOCU LAYER SKIES WERE CLEAR OVER THE MTS/DESERTS. SURFACE
PRESSURE GRADIENTS CONTINUED TO TREND ONSHORE AT 4-6 MBS TO THE
DESERTS. STILL...AT 8 AM PDT...MOST AREAS REPORTED WINDS UNDER 10
MPH WITH A FEW GUSTY SPOTS ON THE DESERT SLOPES. THE 12Z MIRAMAR
SOUNDING HAD A 6.5 DEGREE C INVERSION BASED AT 2300 FT AGL...AND A
SECOND 2 DEGREE C INVERSION BASED NEAR 11.5K FT. WINDS WERE LIGHT
AND VARIABLE BELOW 4K FT AND THE PW WAS 0.76 INCH.

LOOKS LIKE IT WILL BE ANOTHER FINE DAY ACROSS THE REGION WITH MOSTLY
LIGHT WINDS...SUNNY TO PARTLY CLOUDY SKIES...AND MAX TEMPS A BIT
LOWER THAN YESTERDAY. THE ONLY CONCERN WILL BE FOR CUMULUS
DEVELOPMENT OVER THE SAN DIEGO COUNTY MTS. AT THIS TIME...IT APPEARS
THE HIGHER INVERSION WILL CAP ANY MODERATE CONVECTION...AND WITH
LIMITED MOISTURE AVAILABILITY...ANY SHOWERS THAT MANAGE TO DEVELOP
SHOULD BE ISOLATED AND LIGHT. WINDS WILL BECOME GUSTY AGAIN LATE IN
THE DAY THROUGH THE PASSES AND INTO THE DESERT AREAS.

OVERNIGHT INTO MON...SOME ADDITIONAL BUILDING OF THE MARINE LAYER IS
EXPECTED FOR MORE EXTENSIVE LOW CLOUDS WELL INLAND...OTHERWISE SKIES
WILL BECOME FAIR AND TEMPERATURES WILL BE SEVERAL DEGREES BELOW
AVERAGE INLAND.

LOOKS LIKE A COOL WEEK IS SHAPING UP...EVEN AS THE WEAK LOW PRESSURE
AREA OFFSHORE MOVES AWAY FROM THE AREA MON NIGHT. MODELS SHOW A MUCH
COLDER...LONGWAVE TROUGH TAKING SHAPE ACROSS THE STATE THROUGH FRI.
THE TROUGH IS CURRENTLY OVER THE GULF OF ALASKA...BUT WILL TRACK
INTO THE PACNW ON TUE...AND THEN DIVE ALMOST DUE SOUTH INTO CENTRAL
CA BY FRI. THERE IS STILL SOME SPREAD IN THE MODEL SOLUTIONS
REGARDING THE EXACT TRACK AND TIMING...BUT THERE IS CONSENSUS ON THE
PATTERN TO BRING BLUSTERY AND COOLER WEATHER ACROSS SOCAL TO END THE
WORK WEEK.

THE 00Z ECMWF MODEL CONTINUES TO BE THE MOST AGGRESSIVE WITH THE
DEEPENING OF THE SYSTEM WHICH RESULTS IN SLIGHTLY SLOWER MOVEMENT AS
IT CUTS OFF OVER CENTRAL CA...BUT THE 06Z GFS IS NOT TOO MUCH WEAKER
AND FASTER SO CONFIDENCE IS BUILDING IN THE OUTCOME FOR SOCAL.

FOR WINDS...LOOK FOR A GRADUAL INCREASE IN WESTERLY WINDS MON
THROUGH TUE. THEN...BY WED AFTERNOON A SFC PRESSURE GRADIENT OF
AROUND 10 MBS DEVELOPS FROM SAN DIEGO TO NV. THIS SHOULD RESULT IN
SOME WIND GUSTS OVER 40 MPH IN WIND PRONE AREAS LATE IN THE DAY.
STRONGER WINDS ARE LIKELY ON THU BUT THIS IS BEYOND THE HIRES MODELS
AT THIS POINT SO ONCE WE GET CLOSER...A BETTER ESTIMATION IS LIKELY.
BUT FOR NOW...IT LOOKS LIKE AT LEAST ADVISORY STRENGTH WINDS WILL
DEVELOP OVER THE MTS/DESERTS. CONTINUED BREEZY/WINDY ALL AREAS ON
FRI WHEN SOME MOUNTAIN WAVES COULD DEVELOP OVER THE DESERT SLOPES.

PRECIPITATION...AT THIS TIME...AMOUNTS LOOK TO BE LIGHT BASED ON THE
TRACK OF THIS SYSTEM...BUT THE MARINE LAYER IS FORECAST TO DEEPEN
WELL ABOVE 5000 FT SO THERE WILL BE A CHANCE FOR SOME LIGHT SHOWERS
BREAKING OUT ALONG AND WEST OF THE MTS THU NIGHT THROUGH FRI NIGHT.
POPS ARE CURRENTLY QUITE LOW BASED ON UNCERTAINTY AND MODEL
RESOLUTION BUT BOTH OF THE LATEST OPERATIONAL RUNS OF THE GFS/ECMWF
SUGGEST A 90+ KT JET WILL SWING OVER THE REGION ON FRI. IF THAT
HAPPENS...IT IS HARD TO BELIEVE WE WOULD NOT HAVE SUFFICIENT DYNAMICS
TO DRIVE SOME PRECIP DEVELOPMENT FOR A FEW HOURS.

THE SYSTEM IS FORECAST TO REMAIN PROGRESSIVE THROUGH NEXT WEEKEND SO
LOOK FOR FAIR SKIES AND A WARMER WEATHER THEN.

&&

.AVIATION...

031530Z...COAST/VALLEYS...OVC-BKN STRATUS 35-45 SM INLAND...WITH
BASES 2000-2500 FT MSL...TOPS 2600-3000 FT MSL...AND LOCAL VIS 3-5
SM...WILL GRADUALLY CLEAR TO THE COAST THROUGH 1900 UTC. THE MARINE
LAYER INVERSION STRENGTH IS ABOUT 7 DEGREES. 1900-04/0000
UTC...UNRESTRICTED VIS WITH WITH FEW CLOUDS AOA 10000 FT
MSL...EXCEPT SCT TO LOCALLY BKN CLOUDS 2500-3000 FT MSL POSSIBLY
LINGERING WITHIN 10 SM OF THE COAST. 04/0000-1500 UTC...STRATUS
MOVING BACK INLAND DEEP INTO THE VALLEYS...WITH BASES 2500-3000 FT
MSL AND TOPS 4000-4500 FT MSL. FORECAST CONFIDENCE MODERATE-TO-HIGH.

MTNS/DESERTS...UNRESTRICTED VIS THROUGH MONDAY MORNING...EXCEPT FOR
SOME MTN OBSCURATION OF COASTAL SLOPES BELOW 4500 FT MSL ELEVATION
DEVELOPING AFTER 04/0300 UTC DUE TO LOW CLOUDS INTERSECTING TERRAIN.
ELSEWHERE...MOSTLY SKC THROUGH MONDAY MORNING...EXCEPT FOR SOME SCT
CLOUDS AROUND 5000 FT MSL OVER THE SAN DIEGO COUNTY DESERTS THIS
MORNING...AND SCT-BKN CLOUDS BETWEEN 10000 AND 15000 FT MSL
DEVELOPING OVER THE MTNS DURING THE 1800-04/0000 UTC TIME-FRAME.
AFTER 04/0000 UTC...20-25 KT WEST WINDS WITH GUSTS TO 35 KT OVER MTN
RIDGES...THROUGH AND BELOW CANYONS/PASSES...ALONG DESERT SLOPES AND
INTO ADJACENT LOWER DESERT AREAS...WILL PRODUCE MOD-STG UDDFS/LLWS
OVER AND EAST OF THE MTNS.

&&

.MARINE... 830 AM...NO HAZARDOUS MARINE WEATHER IS EXPECTED THROUGH
THURSDAY. A TROUGH APPROACHING FROM THE NORTH WILL LIKELY BRING
BREEZY NORTHWEST WINDS THURSDAY...WITH GUSTS OF 20 TO LOCALLY 25 KT
POSSIBLE.

&&

.BEACHES... 830 AM...SWELL AND SURF IS ON THE RISE THIS MORNING...AS
NEARSHORE BUOY REPORTS SHOW SOUTH-SOUTHWEST SWELLS AT 4 FT WITH A
PERIOD OF 22 SECONDS...AND SURFLINE SURF OBSERVATIONS SHOWING 4 TO 7
FOOT SURF IN ORANGE COUNTY...AND 8 TO 12 FOOT SURF AT THE WEDGE.
LOOKING AT THE SPECTRAL DENSITY PLOTS...TWO DISTINCT LARGE SPIKES IN
SWELL ENERGY ARE APPARENT...ONE AT A PERIOD OF AROUND 22
SECONDS...AND ANOTHER AT AROUND 17 SECONDS. THIS INDICATES THAT THE
TWO LONG PERIOD SOUTH-SOUTHWEST SWELLS HAVE TAKEN OVER. THESE SWELLS
WILL CONTINUE TO BUILD AND FILL-IN THROUGH THE DAY TODAY AND PEAK
LATE TODAY THROUGH MONDAY. THE COMBINATION OF THE TWO SWELLS WILL
BRING HAZARDOUS CONDITIONS TO LOCAL BEACHES...WITH SURF OF 6-10 FEET
AND 12 FOOT SETS IN ORANGE COUNTY AND NORTHERN SAN DIEGO COUNTY...IN
ADDITION TO POWERFUL RIP AND LONGSHORE CURRENTS...BEACH EROSION AND
POSSIBLE MINOR TIDAL FLOODING OF LOW-LYING VULNERABLE COASTAL AREAS
DURING THE EVENING HIGH TIDES. THE SMALLER ENERGY SWELL SHOULD DROP-
OFF ON TUESDAY...BUT THE LARGER SWELL WILL STILL BE GOING
STRONG...AT 4-5 FT/16-17 SECONDS...AND SO HIGH SURF SHOULD CONTINUE
THAT DAY. IT IS NOT UNTIL WEDNESDAY THAT THE SWELL IS EXPECTED TO
DROP BELOW 4 FEET...WITH SURF FALLING AS WELL. THE SWELL WILL THEN
CONTINUE TO FALL INTO THE END OF THE WORK-WEEK. A HIGH SURF ADVISORY
IS IN EFFECT THROUGH TUESDAY EVENING. PLEASE SEE LAXCFWSGX FOR
FURTHER DETAILS. &&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...HIGH SURF ADVISORY UNTIL 11 PM PDT TUESDAY FOR ORANGE COUNTY
     COASTAL AREAS-SAN DIEGO COUNTY COASTAL AREAS FOR THE BEACHES.

PZ...NONE.

&&

$$

PUBLIC...JAD
AVIATION/MARINE/BEACHES...HARRISON


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