Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 171618
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
917 AM PDT WED SEP 17 2014

.SYNOPSIS...
HOT AND HUMID WEATHER WILL CONTINUE TODAY. THE HUMID AND UNSTABLE
ATMOSPHERE WILL BRING A CHANCE OF THUNDERSTORMS TO THE
MOUNTAINS...DESERTS AND MAYBE PORTIONS OF THE VALLEYS LATE THIS
MORNING THROUGH THIS AFTERNOON...WITH FLASH FLOODING POSSIBLE. A LOW
PRESSURE SYSTEM WILL MOVE INTO THE REGION THURSDAY THROUGH THE
WEEKEND WHICH WILL BRING A DRYING AND COOLING TREND AND A RETURN OF
THE MARINE LAYER...WITH PATCHY COASTAL AND VALLEY LOW CLOUDS DURING
THE NIGHTS AND MORNINGS. STRONGER ONSHORE FLOW WILL BRING GUSTY WEST
WINDS IN THE MOUNTAINS AND DESERTS THURSDAY EVENING THROUGH FRIDAY
MORNING. HIGHER PRESSURE ALOFT WILL RE-DEVELOP EARLY NEXT
WEEK...BRINGING WARMER WEATHER.

&&

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

VISIBLE SATELLITE IMAGERY THIS MORNING SHOWS SOME CUMULUS CLOUDS
STARTING TO DEVELOP OVER THE MOUNTAINS...WITH SOME DEBRIS CLOUDS
OVER BAJA AND IMPERIAL COUNTY. THE 12Z MIRAMAR SOUNDING SHOWS
PLENTIFUL MOISTURE...AT 1.73 INCHES OF PRECIPITABLE...WITH 1232 J/KG
OF SURFACE BASED CAPE AND A LIFTED INDEX OF -2.1. CURRENTLY...THE
GPS MET PRECIPITABLE WATER SENSORS INDICATE AROUND 1.5 INCHES OF
PRECIPITABLE WATER WEST OF THE MOUNTAINS...AND AROUND 1.7 INCHES OF
PRECIPITABLE WATER IN THE DESERTS...SO IT DOES APPEAR THAT MOISTURE
IS ON THE DECREASE. THE LOW-LEVEL FLOW FROM THE MIRAMAR SOUNDING
SHOWS NORTH TO NORTHEAST WINDS...WITH NORTHWEST WINDS ABOVE 600 MB.
THUS...THERE COULD BE ENOUGH FLOW TO BRING SOME THUNDERSTORMS INTO
THE VALLEYS TODAY...BUT THE MAIN AREA FOR THUNDERSTORMS SHOULD BE
OVER THE MOUNTAINS AND DESERTS. SPC MESOANALYSIS SHOWS 500-1000 J/KG
OF MOST UNSTABLE CAPE OVER THE AREA...SO IT IS NOT QUITE AS UNSTABLE
AS IT WAS YESTERDAY WHEN THERE WAS 2000-3000 J/KG. THERE IS A BIT
MORE MOISTURE INDICATED IN THE LOW-LEVELS COMPARED TO
YESTERDAY...BUT STILL SOMEWHAT OF AN INVERTED V PROFILE...WHICH
MEANS THAT SOME STRONG DOWNDRAFT GUSTS WILL STILL BE POSSIBLE FROM
THUNDERSTORMS TODAY. THE MAIN THREAT HOWEVER SHOULD BE FLASH
FLOODING IN THE MOUNTAINS AND DESERTS. MODEL INDICATED 700-500 MB
WINDS OF ONLY 5-10 KT SHOULD RESULT IN SLOW-MOVING THUNDERSTORMS
TODAY...WHICH INCREASES THE FLASH FLOOD THREAT. THUS...A FLASH FLOOD
WATCH GOES INTO EFFECT AT 10 AM TODAY AND CONTINUES THROUGH 8 PM FOR
THE MOUNTAINS AND DESERTS. THERE IS STILL ENOUGH MOISTURE IN THE
AREA THIS MORNING TO RESULT IN RATHER HIGH LOW TEMPERATURES FROM
OVERNIGHT INTO THIS MORNING...AS OUR OFFICE HAS A LOW OF ONLY 80
DEGREES THIS MORNING. IT SHOULD BE ANOTHER HOT DAY TODAY...BUT NOT
QUITE AS BAD AS THE PAST FEW DAYS...AS ALL MODELS INDICATE COOLING
OCCURRING.

WATER VAPOR IMAGERY SHOWS CONVECTION ASSOCIATED WITH TROPICAL STORM
ODILE MOVING OVER SONORA TO THE EAST-NORTHEAST AND A TROUGH OFF THE
NORTHERN CALIFORNIA COAST. THIS TROUGH WILL SLOWLY APPROACH THE WEST
COAST TODAY INTO TOMORROW...WITH A CLOSED LOW SPLITTING OUT OF THE
TROUGH AND MOVING INTO A POSITION NEAR POINT CONCEPTION BY SATURDAY
AND THEN MOVING OFF TO THE NORTHEAST SUNDAY. LOCAL WRF INDICATES A
RETURN OF THE MARINE LAYER TONIGHT AS ONSHORE FLOW AND WESTERLY FLOW
ALOFT KICKS IN. THIS SHOULD BRING SOME PATCHY LOW CLOUDS INTO THE
COAST AND VALLEY SECTIONS TONIGHT INTO TOMORROW MORNING. THE TROUGH
WILL ALSO COOL THINGS DOWN SIGNIFICANTLY TOMORROW AND MORE-SO ON
FRIDAY...WITH DAY-TIME HIGHS A FEW DEGREES BELOW NORMAL ON FRIDAY.
THE TROUGH WILL ALSO GENERATE SOME STRONGER ONSHORE PRESSURE
GRADIENTS...RESULTING IN GUSTY WEST WINDS IN THE MOUNTAINS AND
DESERTS THURSDAY EVENING THROUGH FRIDAY MORNING...WITH GUSTS OF
40-45 MPH LIKELY...AND ISOLATED 50 MPH GUSTS. WITH THE DEEPENING
TROUGH OVER THE AREA...THE MARINE LAYER LOOKS TO DEEPEN AS
WELL...WITH NIGHT AND MORNING CLOUDS MOVING DEEP INTO THE VALLEYS
THURSDAY NIGHT THROUGH AT LEAST SATURDAY MORNING.

AS THE LOW MEANDERS NEAR POINT CONCEPTION SATURDAY INTO EARLY
SUNDAY...MODELS INDICATE MOISTURE GETTING PULLED UP FROM THE SOUTH
EAST OF THE AREA...WHICH MEANS THAT WE WILL PROBABLY STAY DRY.
HOWEVER...IF ENOUGH MOISTURE SNEAKS WEST INTO OUR FORECAST
AREA...THEN THE DYNAMICS PROVIDED BY THE LOW COULD BRING SOME
PRECIPITATION TO SOUTHERN CALIFORNIA. THE FORECAST REMAINS DRY FOR
NOW. TEMPERATURES WILL LIKELY BE SIMILAR TO FRIDAY THIS WEEKEND.

FOR MONDAY THROUGH TUESDAY...A WEST-TO-EAST ORIENTED RIDGE MAY BUILD
OVER THE AREA...WHICH WOULD BRING WARMING AND A MUCH SHALLOWER
MARINE LAYER.

&&

.AVIATION...
171600Z...COAST...VFR WITH FEW MID-LEVEL CLOUDS THROUGH THIS
EVENING. PATCHY STRATUS...WITH BASES AROUND 1200 FT MSL AND TOPS
NEAR 1800 FT MSL...WILL DEVELOP ALONG THE COAST TONIGHT...AND PUSH
AROUND 15 SM INLAND BY MID THURSDAY MORNING. VISIBILITY WILL LOWER
TO AROUND 1-3 SM FROM BR WHERE LOW CLOUDS NEAR HIGHER TERRAIN.
CONFIDENCE IN STRATUS DEVELOPING ALONG THE COAST TONIGHT IS
LOW-MODERATE.

VALLEYS/MOUNTAINS/DESERTS...VFR CONDITIONS THOUGH THIS MORNING.
SCATTERED +SHRA AND +TSRA WILL DEVELOP OVER THE AREA THIS AFTERNOON
THROUGH THIS EVENING. CLOUD BASES WILL BE AROUND 6000 FT MSL...WITH
TOPS TO 35000 FT MSL. STRONG UP/DOWNDRAFTS...GUSTY SURFACE
WINDS...LIGHTENING...SMALL HAIL...AND REDUCED VISIBILITY DUE TO +RA
WILL BE POSSIBLE NEAR STORMS. FEW-SCT MID-LEVEL CLOUDS WILL BE
POSSIBLE TONIGHT.

&&

.MARINE...
900 AM...BREEZY NORTHWEST WINDS TO 20 KT WILL DEVELOP OVER THE OUTER
COASTAL WATERS THURSDAY AFTERNOON. OTHERWISE...NO HAZARDOUS MARINE
WEATHER IS EXPECTED THROUGH SUNDAY.

&&

.BEACHES...
AT 9 AM...A LONG PERIOD SOUTHERLY SWELL WILL CONTINUE TO PRODUCE
STRONG RIP AND LONGSHORE CURRENTS...AS WELL AS ELEVATED
SURF...THROUGH THURSDAY. SURF OF 4 TO 6 FEET WITH LOCALLY HIGHER
SETS WILL CONTINUE ON EXPOSED SOUTHWEST FACING BEACHES. THE SWELL
WILL SLOWLY LOWER FRIDAY INTO THE WEEKEND...DIMINISHING THE SURF AND
RIP CURRENT THREAT. A BEACH HAZARDS STATEMENT FOR ELEVATED SURF AND
STRONG RIP AND LONGSHORE CURRENTS REMAINS IN EFFECT THROUGH THURSDAY
EVENING.

&&

.SKYWARN...
SKYWARN ACTIVATION MAY BE NEEDED LATE THIS MORNING INTO THE
AFTERNOON.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...FLASH FLOOD WATCH THROUGH THIS EVENING FOR THE APPLE AND LUCERNE
     VALLEYS...COACHELLA VALLEY...RIVERSIDE COUNTY MOUNTAINS...
     SAN BERNARDINO COUNTY MOUNTAINS...SAN DIEGO COUNTY
     DESERTS...SAN DIEGO COUNTY MOUNTAINS.

     BEACH HAZARDS STATEMENT THROUGH THURSDAY EVENING FOR THE BEACHES
     IN THE ORANGE COUNTY COASTAL AREAS...SAN DIEGO COUNTY
     COASTAL AREAS.

PZ...NONE.

&&

$$

PUBLIC...HARRISON
AVIATION/MARINE/BEACHES...JJT





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