Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 032015
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
115 PM 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...

ISOLATED SHOWERS POSSIBLE OVER THE MOUNTAIN PEAKS THIS AFTERNOON...

THE MARINE CLOUDS CLEARED BY MIDDAY...LEAVING SUNNY SKIES OVR THE
ENTIRE REGION...WITH THE EXCEPTION OF THE MOUNTAIN PEAKS WHERE
CUMULUS WERE FORMING IN THE HEAT OF THE DAY. SURFACE PRESSURE
GRADIENTS WERE TRENDING ONSHORE AT 4-6 MBS TO THE DESERTS. AT NOON
PDT...MOST AREAS REPORTED WIND GUSTS UNDER 20 MPH...EXCEPT THE
WINDIER MOUNTAIN RIDGES AND PASSES...AND ADJACENT DESERT AREAS WHERE
SOME GUSTS WERE IN THE 25-30 MPH RANGE.

THERE IS A CHANCE SOME OF THE BUILDING CUMULUS OVER THE MTS MAY POP
AN ISOLATED LIGHT SHOWER OR TWO. THE LATEST DEWPOINT SURGE AT
JULIAN EDITED INTO THE 12Z MIRAMAR SOUNDING SUGGESTS THERE IS SOME
POTENTIAL TO BREAK THE ELEVATED CAP SO SLIGHT CHANCE POPS HAVE BEEN
ADDED OVER THE PEAKS INTO THIS EVENING. 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.

IT WILL BE A COOLER WEEK AHEAD...EVEN AS THE WEAK LOW PRESSURE AREA
OFFSHORE MOVES AWAY FROM THE AREA MON NIGHT. BECAUSE 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. THE 12Z GFS SEEMS TO BE TRENDING
CLOSER TO THE ECMWF MODEL SO CONFIDENCE IS BUILDING IN THE OUTCOME
FOR SOCAL.

FOR WINDS...LOOK FOR A GRADUAL INCREASE IN WESTERLY WINDS MON
THROUGH TUE. BY TUE AFTERNOON A SFC PRESSURE GRADIENTS TO THE
DESERTS LOOK SUFFICIENT FOR SOME WIND GUSTS OF 40 MPH OR MORE IN
WIND PRONE AREAS LATE IN THE DAY. STRONGER WINDS ARE POSSIBLE 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 BENEATH A STRONG
JET.

PRECIPITATION...AT THIS TIME...AMOUNTS LOOK TO BE LIGHT BASED ON THE
TRACK OF THIS SYSTEM...BUT THE MARINE LAYER IS FORECAST TO DEEPEN
ABOVE 5000 FT...SO THERE WILL BE A CHANCE FOR SOME LIGHT SHOWERS
BREAKING OUT ALONG AND WEST OF THE MTS WED NIGHT THROUGH FRI NIGHT.
THE MODEL PW FIELD IS QUITE LOW OVER THE REGION...CONSEQUENTLY NOT
MUCH OF ANY PRECIP IS BEING GENERATED. WITH THIS IN MIND...POPS ARE
CURRENTLY QUITE LOW. BUT BOTH OF THE LATEST OPERATIONAL RUNS OF THE
GFS/ECMWF SUGGEST A CYCLONICALLY CURVED...90 KT JET WILL WILL SWING
OVER THE REGION ON FRI...PLACING NORTHERN PORTIONS OF THE CWA INTO
A FAVORED AREA OF LIFT AND INSTABILITY. IF THAT HAPPENS...IT IS HARD
TO BELIEVE WE WOULD NOT HAVE SUFFICIENT DYNAMICS TO DRIVE SOME
PRECIP DEVELOPMENT FOR A FEW HOURS. BASED ON THE CURRENT TIMING...
THE BEST CHANCE FOR THAT MEASURABLE PRECIP WOULD BE ON FRI MORNING.

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

&&

.AVIATION... 032007Z...COAST/VALLEYS...THROUGH 04/0000
UTC...UNRESTRICTED VIS WITH WITH FEW CLOUDS AOA 10000 FT
MSL...EXCEPT FEW-SCT CLOUDS 2500-3000 FT MSL LINGERING WITHIN 10 SM
OF THE SAN DIEGO 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. MARINE LAYER INVERSION STRENGTH OF AROUND 5 DEG C.
STRATUS CLEARING BACK TO THE COAST DURING THE 04/1500-1900 UTC TIME-
FRAME. 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...SOME SCT-FEW CLOUDS AROUND 5000 FT MSL OVER THE DESERTS
THIS AFTERNOON...AND SCT-BKN CLOUDS BETWEEN 10000 AND 15000 FT MSL
OVER THE MTNS WITH A POSSIBLE EMBEDDED SHOWER OR TWO. SKIES
GRADUALLY CLEARING AFTER 04/0000 UTC. 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... 107 PM...NO HAZARDOUS MARINE WEATHER IS EXPECTED THROUGH
FRIDAY. A TROUGH APPROACHING FROM THE NORTH WILL LIKELY BRING BREEZY
NORTHWEST WINDS THURSDAY...WITH GUSTS OF 20 TO LOCALLY 25 KT
POSSIBLE.

&&

.BEACHES... 107 PM...SWELL AND SURF CONTINUE TO RISE THIS
AFTERNOON...AS NEARSHORE BUOY REPORTS SHOW SOUTH-SOUTHWEST SWELLS AT
4-5 FT WITH A PERIOD OF 22 SECONDS...AND LIFEGUARD AND SURFLINE SURF
OBSERVATIONS SHOWING 5 TO 8 FOOT SURF IN ORANGE COUNTY...4 TO 7 FOOT
SURF IN SAN DIEGO COUNTY...AND 10 TO 15 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 AFTERNOON 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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