000
FXUS66 KSGX 172033
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
133 PM PDT FRI MAY 17 2013

.SYNOPSIS...
A TROUGH OF LOW PRESSURE ALOFT WILL CONTINUE TO MOVE ACROSS THE
REGION INTO TOMORROW MORNING. A DEEP MARINE LAYER MAY RESULT IN SOME
PATCHY DRIZZLE AT TIMES...AND A FEW LIGHT SHOWERS ARE POSSIBLE IN
THE MOUNTAINS THROUGH THIS EVENING WITH THE PASSAGE OF THE TROUGH.
OTHERWISE...DRY AND COOLER WITH GUSTY WESTERLY WINDS IN THE
MOUNTAINS AND DESERTS. BUILDING HIGH PRESSURE SATURDAY AFTERNOON
THROUGH MONDAY WILL BRING DRYING AND WARMING...ALONG WITH A
SHALLOWER MARINE LAYER. COOLING TREND FOR TUESDAY THROUGH THE REST
OF THE WORK-WEEK AS THE MARINE LAYER DEEPENS AND ONSHORE FLOW
STRENGTHENS.

&&

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

A TROUGH MOVING IN ALONG THE WEST COAST...AS INDICATED BY WATER
VAPOR IMAGERY...BROUGHT A DEEP MARINE LAYER AND SOME DRIZZLE EARLIER
TODAY. HOWEVER...STRATUS FROM THIS MORNING HAS PARTIALLY CLEARED
THIS AFTERNOON...LEAVING BEHIND SOME SCATTERED CUMULUS. ALSO...THE
MID-TO-HIGH LEVEL MOISTURE WHICH RESULTED IN A BAND OF MID-TO-HIGH
CLOUDS OVERNIGHT LAST NIGHT INTO THIS MORNING HAS SINCE MOVED OFF TO
THE EAST OF OUR AREA. BECAUSE OF THIS...AND BECAUSE NO SHOWER
ACTIVITY IS EVIDENT ON SATELLITE OR RADAR...HAVE TAKEN OUT SHOWER
CHANCES FOR THIS AFTERNOON FOR A MAJORITY OF THE AREA. THE ONLY SPOT
THIS AFTERNOON WITH A SLIGHT CHANCE OF SHOWERS ARE THE COASTAL
SLOPES OF THE SAN BERNARDINO MOUNTAINS...WHICH CURRENTLY HAS BROKEN
TO OVERCAST CLOUDS WHICH MAY DROP SOME BRIEF LIGHT RAINFALL THIS
AFTERNOON. HOWEVER...CONFIDENCE IS LOW IN THAT OCCURRING. SOME HIGH
RES MODELS INDICATE THAT THERE MAY BE A LIGHT SHOWER OR TWO ALONG
AND WEST OF THE COASTAL SLOPES THROUGH THIS EVENING AS THE TROUGH
CONTINUES TO MOVE SLOWLY EAST...AND SO HAVE LEFT IN A SLIGHT CHANCE
OF SHOWERS IN THE FORECAST. ANY ADDITIONAL RAINFALL AMOUNTS WILL BE
VERY LIGHT...WITH LESS THAN FIVE HUNDREDTHS OF AN INCH.

THE TROUGH IS ALSO PRODUCING STRONG ONSHORE FLOW TO THE AREA...WITH
SURFACE PRESSURE GRADIENTS FROM SAN DIEGO TO THERMAL OF 7.4 MB
ONSHORE. THE GRADIENTS SHOULD INCREASE FURTHER THROUGH THE
DAY...PEAKING LATER THIS AFTERNOON THROUGH THIS EVENING. ALTHOUGH
THE GRADIENTS MAY END UP BEING SLIGHTLY WEAKER THAN
YESTERDAY...CONSIDERING THAT THERE WERE A COUPLE SPOTS IN THE
COACHELLA VALLEY THAT GUSTED INTO THE LOW 60S YESTERDAY
EVENING...AND THAT HIGH RES MODELS WERE SUPPORTING GUSTS IN THE
45-50 MPH RANGE...A WIND ADVISORY FOR THE LOWER MOUNTAINS AND
DESERTS REMAINS IN EFFECT THROUGH EARLY SATURDAY MORNING. WINDS WILL
BE STRONGEST THROUGH AND BELOW THE SAN GORGONIO PASS AND ALONG AND
NORTH OF INTERSTATE 10 IN THE COACHELLA VALLEY.

THE MARINE LAYER SHOULD BE AT A SIMILAR DEPTH TONIGHT...AS THE
TROUGH DOES NOT QUITE MOVE OUT OF THE AREA YET...AND A PERSISTENT
COASTAL EDDY CONTINUES. HOWEVER...HIGH PRESSURE SHOULD START TO
BUILD OVER THE REGION BY LATE SATURDAY MORNING AS THE TROUGH FINALLY
EXITS TO THE EAST. THIS SHOULD BRING SOME SMALL WARMING FOR
SATURDAY. WARMING SHOULD CONTINUE INTO MONDAY WITH A RIDGE OVER THE
EASTERN NORTH PACIFIC CONTINUING TO NUDGE INTO OUR AREA. THUS...BY
MONDAY...DAY-TIME HIGH TEMPERATURES MAY REACH SEVERAL DEGREES ABOVE
NORMAL. THE SUBSIDENCE FROM THE INCREASING HIGH PRESSURE ALOFT WILL
ALSO BRING A SHALLOWER MARINE LAYER SATURDAY NIGHT THROUGH TUESDAY
MORNING...WITH NIGHT AND MORNING STRATUS MAINLY OVER COASTAL AREAS
AND WESTERN VALLEY SECTIONS.

A COOLING TREND WILL START ON TUESDAY AND CONTINUE THROUGH FRIDAY AS
A DEEP LOW PRESSURE SYSTEM MOVES INTO THE PACIFIC
NORTHWEST...BRINGING LOWER PRESSURE AND CYCLONIC FLOW ALOFT TO
SOUTHERN CALIFORNIA. THE TROUGH WILL CREATE STRONG ONSHORE PRESSURE
GRADIENTS...WITH GUSTY WEST WINDS IN THE MOUNTAINS AND DESERTS IN
THE AFTERNOONS AND EVENINGS. A DEEPER MARINE LAYER WILL RESULT IN
NIGHT AND MORNING STRATUS MOVING FAR INTO THE INLAND VALLEYS. THE
MARINE LAYER MAY GROW THICK ENOUGH FOR SOME DRIZZLE AS WELL.
DAY-TIME HIGH TEMPERATURES ARE CURRENTLY FORECAST TO FALL TO 10
DEGREES BELOW NORMAL IN MOST LOCATIONS BY FRIDAY.

&&

.AVIATION...
172000Z...LOW CLOUDS ARE SCATTERING OVER THE COASTAL
BASIN...ESPECIALLY IN SAN DIEGO COUNTY. SCT-BKN CLOUDS BETWEEN 3000
AND 4000 FT MSL ARE LINGERING IN MANY AREAS IN ORANGE COUNTY AND THE
INLAND EMPIRE. LOW CLOUDS WILL REFILL THE COASTAL BASIN THIS EVENING
THROUGH TONIGHT AROUND 2000-3000 FT MSL. A FEW LIGHT SHOWERS ARE
POSSIBLE ON COASTAL MOUNTAIN SLOPES LATER THIS AFTERNOON AND THIS
EVENING. SOME COASTAL SLOPE TERRAIN WILL BE OBSCURED AT TIMES
TONIGHT IN CLOUDS AND FOG...MAINLY BETWEEN 2500-4500 FEET. PATCHY
DRIZZLE IS ALSO POSSIBLE WEST OF THE MOUNTAINS EARLY SATURDAY
MORNING. BETTER CLEARING IS EXPECTED SATURDAY AS ONSHORE FLOW
WEAKENS.

WESTERLY WINDS WILL CONTINUE TO GUST AROUND 40 MPH THROUGH MOUNTAIN
PASSES AND ADJACENT DESERT SLOPES THROUGH TONIGHT.

&&

.MARINE...
STRONG NORTHWEST WINDS AND A VERY SHORT PERIOD WIND SWELL WILL
INCREASE IN THE OUTER COASTAL WATERS THIS AFTERNOON AND EVENING AND
CONTINUE OVERNIGHT. A FEW GUSTS WILL REACH 25 KT WHILE CHOPPY
COMBINED SEAS UP TO 7 FEET ARE EXPECTED...ESPECIALLY AROUND SAN
CLEMENTE ISLAND. A SMALL CRAFT ADVISORY REMAINS IN EFFECT UNTIL 5 AM
PDT SATURDAY. WINDS AND SEAS WILL DIMINISH SATURDAY MORNING.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...WIND ADVISORY UNTIL 5 AM PDT SATURDAY FOR THE COACHELLA
     VALLEY...RIVERSIDE COUNTY MOUNTAINS...SAN DIEGO COUNTY
     DESERTS...SAN DIEGO COUNTY MOUNTAINS.

PZ...SMALL CRAFT ADVISORY UNTIL 5 AM PDT SATURDAY FOR THE WATERS
     FROM SAN MATEO POINT TO THE MEXICAN BORDER EXTENDING 30 TO 60
     NM OUT INCLUDING SAN CLEMENTE ISLAND.

&&

$$

PUBLIC...HARRISON
AVIATION/MARINE...TS