Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 261724
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
924 AM PST WED NOV 26 2014

.SYNOPSIS...
HIGH PRESSURE ALOFT AND WEAKENING OFFSHORE FLOW WILL BRING A WARMING
TREND INTO THANKSGIVING DAY WITH WELL ABOVE AVERAGE HIGH
TEMPERATURES FOR THE COAST AND VALLEYS. A RETURN OF ONSHORE FLOW
WILL BRING A COOLING TREND FOR FRIDAY THROUGH THE WEEKEND AND A
RETURN OF NIGHT AND MORNING COASTAL AND VALLEY LOW CLOUDS AND FOG.
FOR MONDAY THROUGH WEDNESDAY OF NEXT WEEK...A PACIFIC LOW PRESSURE
SYSTEM COULD BRING MODERATE TO HEAVY PRECIPITATION.

&&

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

VISIBLE SATELLITE SHOWS CLEAR SKIES ACROSS THE REGION THIS
MORNING...AND WIND OBSERVATIONS INDICATE WEAK OFFSHORE WINDS
OCCURRING AT THE SURFACE. THE 12Z MIRAMAR SOUNDING SHOWS A DRY
PROFILE...WITH SIGNIFICANT 24 HOUR WARMING FROM THE SURFACE TO 700
MB. THIS WARMER AND DRY ATMOSPHERE IS DUE TO THE AFOREMENTIONED
OFFSHORE FLOW AND AN UPPER LEVEL RIDGE ALONG THE CALIFORNIA COAST.
PRESSURE GRADIENTS WILL REMAIN WEAKLY OFFSHORE THROUGH
THURSDAY...WITH SOME LOCAL 35 MPH GUSTS THROUGH THE PASSES/CANYONS
AND ALONG THE COASTAL SLOPES AND FOOTHILLS AT TIMES. DAY-TIME HIGHS
TODAY WILL BE 10-15 DEGREES...AND LOCALLY 20 DEGREES...ABOVE NORMAL.
THANKSGIVING WILL BE THE WARMEST DAY...WITH DAY-TIME HIGHS 10-20
DEGREES ABOVE NORMAL...AS HIGHS REACH INTO THE MID TO UPPER 80S FOR
THE VALLEYS AND AREAS A COUPLE MILES FROM THE COAST.

THE UPPER LEVEL RIDGE WILL BREAK DOWN ON FRIDAY...WITH ZONAL FLOW
ALOFT AND PRESSURE GRADIENTS TURNING BACK ONSHORE. IT IS POSSIBLE
THAT WE COULD START TO SEE SOME FOG ALONG THE COAST AS EARLY AS
FRIDAY MORNING. FRIDAY WILL BE THE START OF A COOLING TREND WHICH
WILL CONTINUE THROUGH THE WEEKEND AS ONSHORE FLOW AT THE SURFACE AND
ZONAL FLOW ALOFT CONTINUE. THE MARINE LAYER WILL DEEPEN AS
WELL...WITH NIGHT AND MORNING LOW CLOUDS/FOG LIKELY MOVING INTO THE
COAST AND WESTERN VALLEYS FRIDAY NIGHT/SATURDAY MORNING...AND THEN
FARTHER INTO THE VALLEYS SATURDAY NIGHT/SUNDAY MORNING AND SUNDAY
NIGHT/MONDAY MORNING. DAY-TIME HIGHS WILL START TO FALL TO NEAR TO
SLIGHTLY BELOW NORMAL FOR THE MOUNTAINS AND WEST ON SUNDAY...AND
REMAINING SLIGHTLY ABOVE NORMAL FOR THE DESERTS.

FOR MONDAY INTO WEDNESDAY...MODELS CONTINUE TO SLOW DOWN THE
PROGRESSION OF THE STORM SYSTEM WHICH WILL BRING MODERATE TO HEAVY
PRECIPITATION TOTALS TO SOUTHERN CALIFORNIA. THE 00Z GEM LOOKS LIKE
AN OUTLIER AT THIS MOMENT...AS IT STARTS PRECIP IN OUR AREA ON
MONDAY...WHICH IS A DAY EARLIER THAN THE GFS AND ECMWF...AND MOVES
THE TROUGH THROUGH CENTRAL CALIFORNIA MUCH QUICKER AS WELL. THE 12Z
GFS IS COMING MORE IN-LINE WITH THE SLOWER 00Z ECMWF. BOTH MODELS
SHOW SOUTHWEST FLOW AHEAD OF THE SYSTEM WHICH IS ABLE TO TAP INTO
SUB-TROPICAL MOISTURE AND BRING IT UP OVER SOUTHERN CALIFORNIA EARLY
TUESDAY MORNING...RESULTING IN WIDESPREAD STRATIFORM RAIN WHICH
CONTINUES INTO LATE TUESDAY. GFS PRECIPITABLE WATER SHOWS 1.3 INCHES
ASSOCIATED WITH THIS SUB-TROPICAL MOISTURE. DURING THIS WARM PORTION
OF THE STORM...SNOW LEVELS LOOK TO REMAIN VERY HIGH AT AROUND
9000-11000 FEET. THE 12 GFS REMAINS QUICKER WITH THE ARRIVAL OF THE
COLD AIR...DROPPING SNOW LEVELS TO AROUND 7000 FEET BY EARLY
WEDNESDAY MORNING...WHILE THE 00Z ECMWF DOES NOT REALLY BRING THE
COLDER AIR INTO THE REGION UNTIL WEDNESDAY AFTERNOON. THUS...MOST OF
THE SNOWFALL IS LIKELY NOT TO OCCUR UNTIL WEDNESDAY...WITH
PRECIPITATION MOSTLY IN THE FORM OF RAIN OVER THE MOUNTAINS ON
TUESDAY. THE 00Z ECMWF REMAINS THE SLOWEST SOLUTION...WITH THE
TROUGH AXIS NOT MOVING INLAND UNTIL WEDNESDAY AFTERNOON...AND
PRECIPITATION CONTINUING THROUGH LATE WEDNESDAY NIGHT. PRECIPITATION
TOTALS FOR THE SYSTEM STILL LOOK LIKE THEY WILL BE
SIGNIFICANT...WITH 1-2 INCHES AT THE COAST...4 INCHES OR GREATER IN
THE MOUNTAINS...AND LESS THAN AN INCH IN THE DESERTS. THE 12Z GFS
BRINGS THE TROUGH AXIS THROUGH THE AREA WEDNESDAY MORNING INTO
WEDNESDAY AFTERNOON...WITH PRECIPITATION ENDING WEDNESDAY EVENING.
THE AMOUNT OF SNOW THAT FALLS WILL LARGELY DEPEND ON HOW MUCH
PRECIPITATION OCCURS AFTER THE COLD AIR MOVES IN. THE ECMWF IS
HEAVIEST WITH THE COLD FRONTAL AND POST-FRONTAL PRECIPITATION...BUT
ALSO BRINGS WET-BULB ZERO TEMPERATURES DOWN TO ONLY 8000 FEET...WITH
SIGNIFICANT SNOWFALL POSSIBLE ABOVE THAT ELEVATION. WEST TO
SOUTHWEST WINDS WILL BECOME GUSTY AS WELL...WITH STRONGEST WINDS IN
THE MOUNTAINS AND DESERTS WHERE 50 MPH GUSTS OR GREATER WILL BE
POSSIBLE. FINALLY...DAY-TIME HIGHS WILL FALL TO SEVERAL DEGREES
BELOW NORMAL BY TUESDAY.

&&

.AVIATION...
261540Z...CLEAR SKIES WITH UNRESTRICTED VIS TODAY AND TONIGHT. LOCAL
SURFACE NORTHEAST WINDS IN FOOTHILLS WILL PRODUCE MODERATE UDDFS AND
ISOLATED LLWS THROUGH 20Z.

&&

.MARINE...
740 AM...NO HAZARDOUS MARINE WEATHER IS EXPECTED THROUGH SUNDAY.

&&

.FIRE WEATHER...
OFFSHORE WINDS ARE ONLY GUSTING IN THE 20 TO 30 MPH RANGE...WITH
ONLY SILL HILL GUSTING TO 35 MPH. ALTHOUGH RELATIVE HUMIDITY IS
STILL ONLY IN THE TEENS AND WILL LOWER INTO THE SINGLE DIGITS AGAIN
TODAY FOR AREAS AWAY FROM THE COAST...THE WEAK WINDS ARE NOT
REACHING RED FLAG CRITERIA...AND MODELS INDICATE THAT WINDS WILL
CONTINUE TO DROP OFF THROUGH THE REST OF THE DAY. THUS...THE RED
FLAG WARNING HAS BEEN CANCELLED.

WEAK OFFSHORE WINDS WILL CONTINUE INTO THURSDAY...WITH POOR
OVERNIGHT RECOVERIES TONIGHT. THE OFFSHORE WINDS AND UPPER LEVEL
RIDGE WILL RESULT IN HIGH TEMPERATURES 10-20 DEGREES ABOVE NORMAL
FOR THANKSGIVING AND MINIMUM HUMIDITY IN THE UPPER SINGLE DIGITS/LOW
TEENS. THIS WILL RESULT IN CONTINUED ELEVATED FIRE WEATHER
CONDITIONS. THEN...ONSHORE FLOW WILL START TO RETURN LATE THURSDAY
NIGHT INTO FRIDAY...WITH SOME INCREASE IN HUMIDITIES AND COOLER
CONDITIONS FOR FRIDAY. COOLING AND INCREASING HUMIDITY WILL CONTINUE
INTO THE WEEKEND AS A TROUGH APPROACHES THE WEST COAST AND THE
MARINE LAYER RETURNS AND DEEPENS. THIS TROUGH WILL EVENTUALLY MOVE
OVER THE AREA EARLY NEXT WEEK...LIKELY BRINGING WIDESPREAD
SIGNIFICANT WETTING PRECIPITATION.

&&

.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/FIRE WEATHER...HARRISON
AVIATION/MARINE...TS





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