Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 202029
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
128 PM PDT SAT SEP 20 2014

.SYNOPSIS...
A SLOW MOVING AREA OF LOW PRESSURE OFF THE COAST WILL CONTINUE
COOLER WEATHER AND A DEEP MARINE LAYER THROUGH SUNDAY. IT MAY ALSO
SPARK A FEW THUNDERSTORMS OVER THE HIGHER MOUNTAINS AND DESERTS OF
SOUTHWEST CALIFORNIA THIS AFTERNOON. THE LOW PRESSURE AREA WILL MOVE
INLAND ON SUN...AND THEN EXIT THE REGION NEXT WEEK AS HIGH PRESSURE
REBUILDS ACROSS THE SOUTHLAND. THE DEEP MARINE LAYER WILL THIN UNDER
THE BUILDING HIGH...AND IT WILL BECOME PROGRESSIVELY WARMER THROUGH
MIDWEEK AS HIGH TEMPERATURES CLIMB BACK ABOVE AVERAGE. AFTERNOON SEA
BREEZES WILL CONTINUE TO PROVIDE RELIEF ALONG THE COAST...BUT
ELEVATED SEA SURFACE TEMPERATURES WILL LIMIT THE COOLING...AND KEEP
IT MILD OVERNIGHT. MUCH COOLER BY THE END OF NEXT WEEK AS A STRONGER
TROUGH ARRIVES WITH GUSTY ONSHORE WINDS.

&&

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

MARINE STRATUS WAS EXTENSIVE ONCE AGAIN THIS MORNING WEST OF THE
MOUNTAINS AND STUBBORN TO BURN OFF ACROSS ORANGE COUNTY AND PORTIONS
OF NW SAN DIEGO COUNTY. SURFACE PRESSURE GRADIENTS WERE ONSHORE 4 TO
5 MBS TO THE EAST...AND WERE TRENDING OFFSHORE FROM NV AT AROUND 3
MBS. LATEST VISIBLE SATELLITE IMAGERY SHOWED CUMULUS ALONG THE
RIDGE LINES OF THE MOUNTAINS. MIDDAY TEMPERATURES WERE A FEW DEGREES
LOWER THAN YESTERDAY DUE TO THE LINGERING MARINE CLOUDS.

SHOULD BE A GREAT SUMMER EVENING WEST OF THE MOUNTAINS...AND ANOTHER
FINE DAY ON SUN. THE MARINE LAYER WILL BE TRENDING SHALLOWER THROUGH
TUE WITH LESS EXTENSIVE NOCTURNAL CLOUDINESS AND A WARMING TREND
INTO MIDWEEK.

A CUT-OFF LOW WAS SPINNING OFF OF POINT CONCEPTION TODAY...WITHIN A
BROAD RIDGE OF HIGH PRESSURE OVER THE EASTPAC AND WESTERN U.S. THE
LOW WILL DRIFT TOWARD THE COAST TODAY AND THEN PULL NE ON SUN AHEAD
OF A STRONGER MID-LATITUDE TROUGH. MODELS ARE KEYING IN ON A VORTMAX
SWINGING AROUND THE SE SIDE OF THE LOW. IT IS FORECAST TO LIFT NE
OVER THE CWA TODAY...PROVIDING INSTABILITY...AND THE POTENTIAL FOR
SHWRS/TSTMS OVER THE NORTHERN MTN/DESERT AREAS OF THE CWA. THE
LIMITING FACTOR WILL BE MOISTURE. BLENDED TPW IMAGERY DOES SHOW SOME
MOISTURE DRIFT FROM THE EAST AHEAD OF THIS FEATURE...BUT IT IS
UNCLEAR AT THIS TIME WHETHER OR NOT IT WILL BE SUFFICIENT TO FUEL
TSTM DEVELOPMENT. LATEST 12Z MODEL RUNS ARE NOT GENERATING ANY
PRECIP HERE...BUT BASED ON THE PATTERN...SLIGHT CHANCE/CHANCE POPS
LOOK APPROPRIATE FOR THE AFTERNOON AND EARLY EVENING. DRY LIGHTNING
STRIKES CANNOT BE RULED OUT EITHER DUE TO LIMITED MOISTURE.

ONCE THE UPPER LOW IS DRAWN INTO THE WESTERLIES...HIGH PRESSURE WILL
REBUILD WITH THE 12Z GFS/EC RUNS SHOWING 590+ DM 500 MB HEIGHTS OVER
SOCAL BY MIDWEEK. THIS WILL BRING WARMER DAYS AND ABOVE AVERAGE HIGH
TEMPERATURES AGAIN...BUT NOT AS HOT AS EARLIER THIS WEEK. THE UPPER-
LEVEL RIDGE IS FORECAST TO REMAIN RATHER FLAT...SO THE THERMAL
TROUGH AT THE SFC SHOULD REMAIN INLAND...PROVIDING ONSHORE FLOW AND
MILDER MARINE AIR ALONG THE COAST.

EVEN THOUGH AUTUMN OFFICIALLY BEGINS TUE EVENING...SUMMER WEATHER
WILL BE THE RULE MUCH OF NEXT WEEK. BUT BY THE END OF THE WEEK...
THE WEATHER MAY BE MORE SEASONALLY APPROPRIATE. THE LATEST GFS/
ECMWF RUNS SHOW THE COLDEST TROUGH OF THE SEASON DEVELOPING OVER THE
EASTPAC AND MOVING THROUGH CA NEXT WEEKEND. THIS WILL BRING BELOW
AVERAGE TEMPERATURES...AND MAY BRING RAIN TO NORTHERN PARTS OF THE
STATE. HOWEVER...THE ELEVATED SEA SURFACE TEMPERATURES WILL BUFFER
THE COOLING FROM THE TROUGH THIS FAR SOUTH...ESPECIALLY NEAR THE
COAST. THE TROUGH WILL ALSO PRODUCE GUSTY WINDS OVER THE MOUNTAINS
AND DESERTS.

&&

.AVIATION...
202100Z...COASTS/VALLEYS...SCT-BKN LOW CLOUDS WITH BASES 2500-3000
FT MSL AND TOPS TO 3500 FT MSL OVER PORTIONS OF ORANGE AND SAN DIEGO
COUNTIES. EXPECT LOW CLOUDS WITH BASES 1500-2500 FT MSL AND TOPS TO
3000 FT MSL TO RETURN TO ALL COASTAL AIRPORTS AROUND 03Z
SUN...SPREADING 20-30 MILES INLAND OVERNIGHT. LOW CLOUDS SHOULD
CLEAR TO THE COAST BETWEEN 17Z AND 19Z SUN.

MOUNTAINS/DESERTS...SCT WITH BASES AOA 8000 FT MSL THIS AFTERNOON.
OTHERWISE...CLEAR WITH UNRESTRICTED VSBY THROUGH TONIGHT.

&&

.MARINE...
200 PM...NO HAZARDOUS MARINE WEATHER IS EXPECTED THROUGH WEDNESDAY.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

$$

PUBLIC...JAD
AVIATION/MARINE...PG












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