Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 311546
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
846 AM PDT MON AUG 31 2015

.SYNOPSIS...
A TROUGH OF LOW PRESSURE ALONG THE WEST COAST WILL BRING COOLING AND
A DEEPER MARINE LAYER THIS WEEK. NOCTURNAL MARINE CLOUDS AND FOG
WILL SETTLE A LITTLE FARTHER INTO THE VALLEYS EACH NIGHT THROUGH
WEDNESDAY MORNING...SLOWLY RETREATING AGAIN OVER THE UPCOMING
HOLIDAY WEEKEND AS THE TROUGH WEAKENS ALOFT. THIS ONSHORE PATTERN
WILL CONTINUE TO SUPPORT GUSTY LATE DAY AND OVERNIGHT WESTERLY WINDS
THROUGH THE PASSES AND ON THE DESERT SLOPES...AND NEAR TO SLIGHTLY
BELOW AVERAGE TEMPERATURES. ELEVATED SEA SURFACE TEMPERATURES WILL
MAKE FOR MILD NIGHTS ALONG THE COASTAL STRIP. A LITTLE WARMER FOR
THE LABOR DAY WEEKEND AND CONTINUED DRY.

&&

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

THERE WAS AN EXPLOSION OF MARINE CLOUDS OVERNIGHT ACROSS THE CA
BIGHT AS AN EDDY CIRCULATION DEVELOPED. THESE CLOUDS HAVE SPREAD
WELL INLAND THIS MORNING...ALONG WITH PATCHY DENSE FOG WHERE THE
CLOUD DECK INTERSECTS THE HIGHER TERRAIN. THE 12Z MIRAMAR SOUNDING
HAD A NEARLY 8 DEGREE C INVERSION BASED AT 1700 FT. THIS WAS SOME
600 FT DEEPER THAN YESTERDAY. UNLIKE THE PAST FEW DAYS...WINDS ALOFT
WERE MORE UNIFORM...VEERING FROM S TO SW WITH HEIGHT. THIS DRY FLOW
HAS LOWERED THE PW TO 0.79 INCH. AT 7 AM PDT...SURFACE PRESSURE
GRADIENTS HAD TURNED NEUTRAL TO NV BUT REMAINED ONSHORE AROUND 5 MBS
TO THE LOWER DESERTS. WIND REPORTS WERE MOSTLY LIGHT...EXCEPT
LOCALLY THROUGH THE WIND-PRONE PASSES.

THE EDDY WILL WEAKEN OVER THE NEXT COUPLE OF DAYS...BUT THE MARINE
CLOUDS AND COOLER WEATHER WILL PERSIST...AS A LOW PRESSURE TROUGH
ALOFT GRADUALLY DEEPENS ALONG THE WEST COAST. THERE ARE SOME MODEL
DIFFERENCES...BUT GENERALLY THE TROUGH REACHES MAXIMUM AMPLITUDE
OVER CA LATE IN THE WEEK...THEN SLOWLY WEAKENS DURING THE LABOR DAY
WEEKEND. COOLEST WEATHER SHOULD BE THU/FRI TIME FRAME...FOLLOWED BY
SLOW WARMING THROUGH EARLY NEXT WEEK.

PRESENT INDICATIONS ARE THAT THE BENIGN PATTERN WILL HOLD TROUGH THE
FIRST TEN DAYS OF SEPTEMBER. THE MODELS INDICATE LITTLE LONGWAVE
MOVEMENT OVER THE WESTERN HEMISPHERE...WITH THE MASSIVE EASTPAC
RIDGE ALONG 160W...AND THE RIDGING OVER CENTRAL N.A. HOLDING. THESE
ARE NO DOUBT HELPING TO ANCHOR THE WEAK TROUGH ALONG THE WEST
COAST...WHICH DEFLECTS ANY MONSOONAL FLOW FARTHER TO THE EAST OF
SOCAL...AND MAINTAINS ONSHORE FLOW AT THE SURFACE WITH SEASONAL
TEMPERATURES.

&&

.AVIATION...
311500Z...COAST/VALLEYS...STRATUS...WITH BASES AROUND 1700 FT MSL
AND TOPS NEAR 2300 FT MSL...WILL CLEAR TOWARDS THE COAST THIS
MORNING AROUND 17Z. A COASTAL EDDY MAY SLOW THE CLEARING. THE
31/12Z MIRAMAR SOUNDING SHOWED AN 8 DEG C MARINE LAYER INVERSION.
LOW CLOUDS WILL REDEVELOP ALONG THE COAST LATE THIS EVENING...WITH
SLIGHTLY HIGHER TOPS AND BASES. VIS OF 1-3 SM BR IS POSSIBLE WHERE
LOW CLOUDS NEAR HIGHER INLAND TERRAIN OVERNIGHT.

MTNS/DESERTS...SKC WITH UNRESTRICTED VIS THROUGH TUE MORNING.

&&

.MARINE...
800 AM...NO HAZARDOUS MARINE WEATHER IS EXPECTED THROUGH FRIDAY.

&&

.BEACHES...
800 AM...AN ELEVATED SOUTHERLY SWELL WILL CREATE A HIGH RISK OF RIP
CURRENTS AND SURF TO 6 FEET ALONG SOUTHERLY-FACING BEACHES IN ORANGE
COUNTY THROUGH THE MIDDLE OF THIS WEEK. A MODERATE RISK OF RIP
CURRENTS AND SLIGHTLY LOWER SURF IS FORECAST FOR SAN DIEGO COUNTY
BEACHES.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.
&&

$$

PUBLIC...JAD
AVIATION/MARINE...JJT


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