Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 182121
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
121 PM PST THU DEC 18 2014

.SYNOPSIS...
ISOLATED SHOWERS POSSIBLE THROUGH THIS AFTERNOON OVER SOME COASTAL
AND VALLEY AREAS. DRY AND MILDER FRIDAY UNDER WEAK RIDGING. A
WEAK TROUGH WILL CREATE A SLIGHT CHANCE OF SHOWERS FRIDAY NIGHT
THROUGH SATURDAY MORNING. A LARGE AREA OF UPPER-LEVEL HIGH
PRESSURE WILL CREATE WARMER WEATHER AND WEAK OFFSHORE FLOW EARLY
NEXT WEEK...WITH ONSHORE FLOW AND NEAR NORMAL HIGH TEMPERATURES BY
MID-NEXT WEEK.

&&

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

AT 1 PM PST...WATER VAPOR SATELLITE IMAGERY DISPLAYED A SHORTWAVE
RIDGE BUILDING INTO CENTRAL CA...AND A TROUGH MOVING INTO THE
PACIFIC NORTHWEST. ALTHOUGH COMPOSITE RADAR SHOWED NO SHOWER
ACTIVITY AROUND THE AREA...SOME ISOLATED LIGHT SHOWERS WERE
MOVING ACROSS COASTAL AND VALLEY AREAS DROPPING VERY LIGHT
PRECIPITATION.

WEAK UPPER-LEVEL RIDGING WILL BUILD OVER THE AREA THROUGH
FRIDAY...WHICH WILL CREATE DRY AND SLIGHTLY WARMER WEATHER OVER SW
CA TONIGHT AND FRIDAY. ANOTHER UPPER-LEVEL TROUGH WILL DIG ACROSS
THE REGION FRIDAY NIGHT INTO SATURDAY MORNING...WHICH WILL
GENERATE A SLIGHT CHANCE FOR SHOWERS FOR MOST AREAS OVER AND WEST
OF THE MOUNTAINS. MODELS THEN PROG AN UPPER-LEVEL RIDGE TO BUILD
AND ANCHOR TO OUR SOUTHWEST FOR EARLY NEXT WEEK. WEAK OFFSHORE
FLOW AND INCREASING THICKNESSES WILL HELP HIGH TEMPERATURES RISE 5
TO 15 DEGREES F ABOVE NORMAL BY TUESDAY. SLIGHT COOLING WILL
DEVELOP CHRISTMAS EVE AS THE RIDGE WEAKENS AND FLOW TRANSITIONS
FROM OFFSHORE TO ONSHORE.

THE 18/1200 UTC ECMWF HAS CHANGED DRASTICALLY IN THE LATEST RUN
AND ACTUALLY AGREES FAIRLY WELL WITH THE GFS SOLUTION. MODELS ARE
NOW BOTH FORECASTING DRY WEATHER WITH BREEZY ONSHORE FLOW IN THE
MOUNTAINS AND DESERTS FOR CHRISTMAS DAY...KEEPING A LOW PRESSURE
SYSTEM WELL TO OUR NORTH. HIGHS WILL MOST LIKELY BE NEAR TO
SLIGHTLY BELOW NORMAL WITH NORTHWEST FLOW ALOFT.

&&

.AVIATION...
182200Z...SCT AND LOCALLY BKN CLOUDS OVER COASTAL BASIN THROUGH
TONIGHT. BASES WILL BE AROUND 3000-5000 FEET MSL WITH SCATTERED
LAYERS UP TO 20000 FEET. LOCAL BKN CIGS 2000-3000 FEET MSL ARE
POSSIBLE BETWEEN 09Z AND 15Z FRI...BUT CONFIDENCE IS NOT HIGH.

&&

.MARINE...
200 PM...NO HAZARDOUS WEATHER CONDITIONS ARE EXPECTED OVER THE
COASTAL WATERS THROUGH MONDAY.

&&

.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...JJT
AVIATION/MARINE...PG







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