Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 181601
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
901 AM PDT THU SEP 18 2014

.SYNOPSIS...
A LOW PRESSURE TROUGH MOVING SLOWLY MOVING THROUGH CENTRAL
CALIFORNIA WILL BRING COOLER WEATHER...LOWER HUMIDITIES AND NIGHT
AND MORNING STRATUS INTO THE COAST AND VALLEYS SECTIONS THROUGH
SUNDAY. STRONGER ONSHORE FLOW FROM THIS TROUGH WILL BRING GUSTY WEST
WINDS TO THE MOUNTAINS AND DESERTS THIS AFTERNOON THROUGH EARLY
FRIDAY MORNING. THE MARINE LAYER MAY BE THICK ENOUGH TO BRING PATCHY
DRIZZLE OVERNIGHT TONIGHT. ISOLATED THUNDERSTORMS MAY FORM OVER THE
MOUNTAINS SATURDAY AFTERNOON DUE TO A POSSIBLE INCREASE IN MOISTURE
FROM THE SOUTH. A WARMING TREND AND SHALLOWER MARINE LAYER IS
EXPECTED FOR THE FIRST HALF OF NEXT WEEK AS HIGH PRESSURE ALOFT
EXPANDS INTO THE REGION.

&&

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

PATCHY STRATUS WAS ABLE TO FORM THIS MORNING ALONG PORTIONS OF THE
COASTAL AND VALLEY AREAS...ACCORDING TO VISIBLE SATELLITE. THE 12Z
MIRAMAR SOUNDING SHOWED A 5 DEGREE MARINE INVERSION AT AROUND 1600
FEET...WITH LESS INSTABILITY THAN THE PAST FEW DAYS...WESTERLY FLOW
THROUGH THE PROFILE...AND A STRONG CAPPING INVERSION AT AROUND 620
MB. SPC MESOANALYSIS ALSO SHOWS NO INSTABILITY OVER OUR AREA...AND
GPS MET PRECIPITABLE WATER SENSORS INDICATE VALUES OF ONLY 1.3
INCHES IN THE DESERTS...AND 1 INCH OR LESS WEST OF THE MOUNTAINS.
THUS...WITH THE DRIER AIR AND INCREASING STABILITY...THERE SHOULD
NOT BE ANY THUNDERSTORMS/SHOWERS DEVELOPING OVER THE MOUNTAINS AND
DESERTS TODAY. WITH THE DRY AIR...AND ONSHORE FLOW...CONDITIONS HAVE
COOLED SIGNIFICANTLY IN ALL AREAS EXCEPT FOR THE DESERTS...WITH
TEMPERATURES 5-15 DEGREES LOWER THAN THEY WERE 24 HOURS AGO.
DAY-TIME HIGHS TODAY WILL LIKELY END UP BEING 5-15 DEGREES LOWER
THAN YESTERDAY IN THESE AREAS AS WELL. ALSO...THE WEAK MARINE
INVERSION SHOULD ALLOW FOR GOOD CLEARING TODAY. HOWEVER...A TROUGH
JUST OFF THE COAST OF NORTH-CENTRAL CALIFORNIA WILL CONTINUE TO
DRIFT SOUTH THROUGH TONIGHT...BRINGING STRENGTHENING OF ONSHORE FLOW
AND A DEEPER MARINE LAYER FOR TONIGHT INTO TOMORROW...WITH STRATUS
MOVING DEEP INTO THE INLAND VALLEYS. THERE ARE STILL INDICATIONS
THAT THE MARINE LAYER MAY BE THICK ENOUGH FOR SOME PATCHY DRIZZLE TO
FORM WEST OF THE MOUNTAINS ALSO. THE ONSHORE PRESSURE GRADIENTS
LOOKS TO PEAK AT AROUND 7 MB FROM SAN DIEGO TO DAGGETT...AND 6 MB
FROM SAN DIEGO TO THERMAL THIS EVENING. THIS WILL LIKELY BE ENOUGH
TO BRING GUSTY WEST WINDS TO THE MOUNTAIN RIDGES...DESERT SLOPES AND
ADJACENT DESERT AREAS THIS AFTERNOON THROUGH EARLY FRIDAY
MORNING...WITH WIND GUSTS OF 35-45 MPH AND LOCALLY 50 MPH.

COOLING WILL CONTINUE ON FRIDAY AS A CLOSED LOW SPLITS OUT OF THE
TROUGH AND ASSUMES A POSITION NEAR POINT CONCEPTION...WITH MOST
PLACES EXPECTED TO BE SEVERAL DEGREES BELOW NORMAL FOR DAY-TIME HIGH
TEMPERATURES. THE LOW WILL THEN SLOWLY MOVE NORTHEAST INLAND THROUGH
CENTRAL CALIFORNIA AND NEVADA LATE SATURDAY INTO SUNDAY.
TEMPERATURES FOR SATURDAY AND SUNDAY MAY BE SLIGHTLY WARMER AS 850
MB TEMPERATURES INCREASE SLIGHTLY. THERES A CHANCE THAT THE LOW
COULD BRING UP ENOUGH MOISTURE FROM THE SOUTH TO BRING SOME
THUNDERSTORMS TO THE MOUNTAINS AND DESERTS SATURDAY AFTERNOON. ITS A
PRETTY SLIM CHANCE THOUGH...AS MODELS SHOW THE BULK OF THE MOISTURE
STAYING TO THE EAST OF OUR AREA. THE MARINE LAYER LOOKS TO REMAIN
DEEP...WITH NIGHT AND MORNING STRATUS MOVING INTO THE INLAND
VALLEYS.

FOR MONDAY THROUGH WEDNESDAY...AN UPPER LEVEL RIDGE TO THE SOUTH
WILL EXPAND INTO THE REGION...BRINGING A WARMING TREND...WITH THE
MARINE LAYER BECOMING INCREASINGLY SHALLOW...WITH NIGHT AND MORNING
STRATUS/FOG MAINLY ALONG THE COAST.

&&

.AVIATION...
181630Z...COAST/VALLEYS...BKN-SCT CLOUDS BASED 1500-2000 FEET
MSL...TOPS 2500 FEET MSL...WILL CLEAR BACK TO OVER THE COASTAL
WATERS BY 18Z. AFTER 01Z THIS AFTERNOON OVC LOW CLOUDS BASED
1800-2500 FEET MSL...TOPS APPROACHING 3000 FEET MSL...WILL MOVE
INLAND...REACHING KRNM/KONT AROUND 08Z TONIGHT. LOW CLOUDS SHOULD
CLEAR SOMEWHAT LATER FRIDAY MORNING COMPARED TO TODAY. CONFIDENCE IN
THE STRATUS ARRIVAL TIME AT THE COASTAL TAFS IS MODERATE FOR THIS
EVENING.

MOUNTAINS/DESERTS...WEST WINDS WITH SFC GUSTS 25-35 KT WILL DEVELOP
OVER THE DESERT MOUNTAIN SLOPES AND ADJACENT DESERT FOOTHILLS THIS
AFTERNOON AND EVENING. OTHERWISE MOSTLY CLEAR WITH UNRESTRICTED
VISIBILITIES THROUGH FRI MORNING.

&&

.MARINE...
845 AM...LOCAL WEST-NORTHWEST WINDS WITH GUSTS TO 20 KT ARE POSSIBLE
OVER THE OUTER COASTAL WATERS THIS AFTERNOON. OTHERWISE...NO
HAZARDOUS MARINE WEATHER IS EXPECTED THROUGH MONDAY.

&&

.BEACHES...
845 AM...A LONG PERIOD SOUTH-SOUTHWEST SWELL WILL CONTINUE TO
PRODUCE ELEVATED SURF AND STRONG RIP AND LONGSHORE CURRENTS TODAY.
SURF OF 4 TO 6 FEET WITH LOCALLY HIGHER SETS LIKELY ON EXPOSED
SOUTHWEST FACING BEACHES. SWELL AND SURF WILL SLOWLY LOWER FRIDAY. A
BEACH HAZARDS STATEMENT REMAINS IN EFFECT THROUGH THIS EVENING.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...BEACH HAZARDS STATEMENT THROUGH THIS EVENING FOR THE BEACHES IN
     THE ORANGE COUNTY COASTAL AREAS...SAN DIEGO COUNTY COASTAL
     AREAS.

PZ...NONE.

&&

$$

PUBLIC...HARRISON
AVIATION/MARINE/BEACHES...SMALL





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