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000
FXUS66 KSGX 042317 CCA
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
125 PM PST WED DEC 4 2013

.SYNOPSIS...
A COLD TROUGH OF LOW PRESSURE WILL REMAIN OVER THE WEST THROUGH THIS
WEEKEND.  DAYTIME TEMPERATURES WILL BE ROUGHLY 10 TO 20 DEGREES
BELOW NORMAL...WITH FROSTY CONDITIONS POSSIBLE EACH NIGHT IN THE
HIGH DESERT AND INLAND VALLEYS.  A FEW ISOLATED SHOWERS MAY DEVELOP
LATE TONIGHT AND ON THURSDAY OVER THE SAN DIEGO COUNTY MOUNTAINS AND
FOOTHILLS...AS ANOTHER DISTURBANCE MOVES THROUGH THE REGION.  A
STRONGER AND COLDER DISTURBANCE WILL RE-ENFORCE THE COLD AIR AND
BRING A BETTER CHANCE OF PRECIPITATION TO THE REGION ON SATURDAY.  A
GRADUAL WARMING TREND WILL THEN DEVELOP FOR NEXT WEEK.

&&

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

WATER VAPOR IMAGERY SHOWS A VERY ELONGATED TROUGH OF LOW PRESSURE
OVER THE WEST THIS AFTERNOON...WITH COLD AND DRIER AIR FILTERING
INTO THE REGION.  AS A RESULT...TEMPERATURES ARE RUNNING UP TO 10
DEGREES COOLER ACROSS THE SOUTHLAND THAN THIS TIME YESTERDAY...WITH
DEW POINT VALUES DROPPING INTO THE TEENS ACROSS THE HIGH DESERT AND
INTO MAINLY THE 30S ELSEWHERE.  THEREFORE...JUST A FEW COLD AIR
CUMULUS CLOUDS ARE LINGERING OVER THE REGION...WITH DRY CONDITIONS
PREVAILING.

THESE COOL AND DRY CONDITIONS WILL ALLOW TEMPERATURES TO QUICKLY
DROP AFTER SUNSET...MAKING FOR A CHILLY EVENING AND AN EVEN COLDER
NIGHT.  IN FACT...FREEZING CONDITIONS WILL DEVELOP ACROSS THE HIGH
DESERT...WITH THE POTENTIAL FOR A HARD FREEZE IN SOME OF THE
COLDER...WIND SHELTERED LOCATIONS.  THEREFORE...A FREEZE WARNING
WILL GO INTO EFFECT FOR THEM TONIGHT.  THE INLAND EMPIRE WILL ALSO
SEE TEMPERATURES FALL INTO THE 30S...AND MAYBE LOCALLY LOWER...WITH
AREAS OF FROST POSSIBLE.  THEREFORE...WILL ALSO ISSUE A FROST
ADVISORY FOR THEM FOR LATE TONIGHT THROUGH TOMORROW MORNING.  SOME
LOCALLY FROSTY CONDITIONS WILL ALSO BE POSSIBLE ACROSS THE COACHELLA
VALLEY AS WELL AS THE SAN DIEGO COUNTY VALLEYS.  HOWEVER...THE HIGH
RESOLUTION MODELS CONTINUE TO HINT AT THE POTENTIAL FOR SOME
ISOLATED SHOWERS OVER THE SAN DIEGO COUNTY COASTAL SLOPES LATE
TONIGHT AND TOMORROW MORNING...AS A DISTURBANCE MOVES THROUGH THE
REGION.  THEREFORE...THINK THERE MAY BE ENOUGH CLOUD COVER TO LIMIT
WIDESPREAD FROST IN THESE AREAS.  THESE COOL DAY TIME AND COLD
OVERNIGHT CONDITIONS WILL THEN CONTINUE INTO THURSDAY AND
FRIDAY...WITH ONLY MINOR FLUCTUATIONS IN TEMPERATURES...SO
ADDITIONAL FROST OR FREEZE PRODUCTS MAY BE NEEDED AGAIN FOR LATE
THURSDAY NIGHT AND INTO FRIDAY.

THE REAL FOCUS OF THE FORECAST THEN TURNS TO FRIDAY NIGHT AND
SATURDAY...AS THE MODELS CONTINUE TO INDICATE A STRONGER AND COLDER
DISTURBANCE DIVING SOUTH THROUGH THE TROUGH.  THE MODELS INITIALLY
GIVE THIS SYSTEM A SLIGHTLY MORE OVER WATER TRAJECTORY BEFORE
CUTTING IT INLAND ACROSS CENTRAL CALIFORNIA...SO IT APPEARS THAT
THERE WILL BE MORE MOISTURE TO WORK WITH...EVEN GIVEN THE COLD AIR
IN PLACE.  THERE WILL ALSO BE GOOD UPPER LEVEL JET SUPPORT AS WELL
AS ANOTHER SURGE OF THE MODIFIED POLAR AIRMASS.  THEREFORE...THINK
THAT THE SHOWERS WILL LIKELY START LATE FRIDAY NIGHT ALONG AND WEST
OF THE MOUNTAINS...WITH THE BRUNT OF THE MOISTURE WILL MOVE ACROSS
THE REGION ON SATURDAY.  THE REAL QUESTION THOUGH IS JUST HOW MUCH
PRECIPITATION WILL WE SEE?  AT THIS TIME...IT APPEARS THAT COASTAL
AND VALLEY LOCATIONS COULD SEE BETWEEN A QUARTER AND A HALF
INCH...WHILE THE MOUNTAINS COULD SEE LOCALLY AMOUNTS AS HIGH AS AN
INCH.  SNOW LEVELS WILL ALSO BE QUITE LOW WITH THIS SYSTEM...LIKELY
AROUND 3000 FEET AND POTENTIALLY AS LOW AS 2500 FEET.  THIS MEANS
THAT THIS SYSTEM HAS THE POTENTIAL TO BE AN EFFICIENT SNOW PRODUCER
FOR THE MOUNTAINS AS WELL...AND MAY NEED TO CONSIDER WINTER WEATHER
PRODUCTS FOR THE MOUNTAINS AND MAYBE EVEN THE HIGH DESERTS IF FUTURE
RUNS CONTINUE TO TREND THIS WAY.  ALTHOUGH SHOWERS WILL LINGER INTO
SATURDAY NIGHT...DRIER CONDITIONS WILL START TO DEVELOP...WITH
ANOTHER COLD DAY PREVAILING ON SUNDAY.

A GRADUAL DRYING AND WARMING TREND WILL THEN DEVELOP FOR THE FIRST
PART OF NEXT WEEK...AS HIGH PRESSURE TRIES TO BUILD BACK ACROSS THE
REGION.

&&

.AVIATION...
042115Z...SCT-BKN CLD LAYERS BETWEEN 3000-4000 FT AND TOPS AROUND
5000 FT MSL WILL CONTINUE WEST OF THE MOUNTAINS THROUGH THE
REMAINDER OF THE DAY...WITH VIS P6SM. SKIES SKC/FEW ELSEWHERE. AFTER
05/0600Z TONIGHT...THE MARINE LAYER WILL DEEPEN WITH BASES AROUND
3000-4000 FT MSL AND TOPS RISING TO 6000-9000 FT MSL. LIGHT SHOWERS
WILL DEVELOP IN THE SAN DIEGO COUNTY AND RIVERSIDE COUNTY MOUNTAINS.
VIS MAY DROP TO BELOW 3SM WHERE CLOUDS INTERSECT THE TERRAIN. IN
ADDITION...CLOUD BASES MAY LOWER TO 2500 UNDER THE RAIN CORES.
ELSEWHERE...UNRESTRICTED VIS AND FEW-SCT CLDS 4000-15000 FT MSL.

&&

.MARINE...
WEST WINDS WILL CONTINUE TO GUST TO BETWEEN 20-25 KT ACROSS THE
OUTER WATERS TONIGHT LASTING THROUGH MID-THURSDAY MORNING. THE STEEP
SEAS AND STRONG WINDS WILL CREATE HAZARDOUS BOATING CONDITIONS FOR
SMALL CRAFT. A SMALL CRAFT ADVISORY FOR THE OUTER WATERS WILL
REMAIN IN EFFECT FOR OUTER WATERS UNTIL 10 AM THURSDAY. WINDS AND
SEAS SHOULD IMPROVE DURING THE DAY THURSDAY.

ANOTHER TROUGH OF LOW PRESSURE MOVING INTO THE REGION SATURDAY WILL
BRING A ROUND OF STRONG WEST TO NORTHWEST WINDS AND STEEP SEAS TO
THE COASTAL WATERS...MAKING FOR HAZARDOUS CONDITIONS FOR SMALL CRAFT
ONCE AGAIN.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...FREEZE WARNING FROM 1 AM TO 9 AM PST THURSDAY FOR THE APPLE AND
     LUCERNE VALLEYS.

     FROST ADVISORY FROM 1 AM TO 9 AM PST THURSDAY FOR THE SAN
     BERNARDINO AND RIVERSIDE COUNTY VALLEYS-THE INLAND EMPIRE.

PZ...SMALL CRAFT ADVISORY UNTIL 10 AM PST THURSDAY FOR THE WATERS
     FROM SAN MATEO POINT TO THE MEXICAN BORDER EXTENDING 30 TO
     60 NM OUT INCLUDING SAN CLEMENTE ISLAND.

&&

$$

PUBLIC...PALMER
AVIATION/MARINE...JT