Area Forecast Discussion
Issued by NWS San Diego, CA

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375
FXUS66 KSGX 291600
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
900 AM PDT FRI APR 29 2016

.SYNOPSIS...
DRY AND A LITTLE WARMER TODAY UNDER WEAK HIGH PRESSURE. A LOW
PRESSURE SYSTEM MOVING SOUTHWARD THROUGH THE WESTERN STATES WILL
BRING COOLING AND GUSTY WINDS FOR THE MOUNTAINS AND DESERTS
SATURDAY WITH A CHANCE OF SHOWERS AND SLIGHT CHANCE OF
THUNDERSTORMS FOR SATURDAY AFTERNOON AND EVENING. DRY AND WARMER
FOR SUNDAY THROUGH TUESDAY WITH HIGH PRESSURE ALOFT OFF THE WEST
COAST...ALTHOUGH A WEAK DISTURBANCE COULD CREATE SOME SHOWER AND
THUNDERSTORM ACTIVITY OVER THE MOUNTAINS AND HIGH DESERTS SUNDAY
AFTERNOON AND EVENING. FOR WEDNESDAY THROUGH FRIDAY...COOLING
WILL SPREAD INLAND WITH INCREASING CLOUDS TOWARD THE END OF THE
WEEK AS A LOW PRESSURE SYSTEM OVER THE EASTERN PACIFIC MOVES
SLOWLY TOWARDS THE WEST COAST. SOME PRECIPITATION COULD OCCUR BY
FRIDAY.

&&

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

A DEEP MARINE LAYER IS IN PLACE THIS MORNING...WITH VISIBLE
SATELLITE INDICATING PATCHY STRATUS OVER THE COAST AND
VALLEYS...WITH MOSTLY WIDESPREAD STRATUS OVER THE COASTAL WATERS.
THE 12Z MIRAMAR SOUNDING SHOWS A MARINE LAYER INVERSION AT AROUND
3000 FEET...WITH NORTHWEST FLOW ALOFT. WATER VAPOR SATELLITE SHOWS
A TROUGH OVER THE INTER-MOUNTAIN WEST...A RIDGE TO OUR
WEST...ALLOWING FOR THE AFOREMENTIONED NORTHWEST FLOW ALOFT OVER
SOUTHERN CALIFORNIA. HI-RES MODELS INDICATE THAT STRATUS SHOULD AT
LEAST PARTIALLY CLEAR OUT TODAY...AND HIGHER 500 MB HEIGHTS MOVING
IN AND SIGNIFICANTLY LESS CLOUD COVER SHOULD RESULT IN HIGHS
SEVERAL DEGREES HIGHER THAN YESTERDAY.

LOCAL WRF SHOWS A COASTAL EDDY SPINNING UP TONIGHT INTO SATURDAY
MORNING AND PERHAPS CONTINUING THROUGH SUNDAY MORNING. THE EDDY
SHOULD HELP BRING STRATUS...POSSIBLY SOMEWHAT PATCHY...THROUGH THE
COAST...VALLEYS...COASTAL SLOPES AND INTO THE PASSES.

ON SATURDAY...MODELS SHOW A LOW MOVING DOWN FROM THE NORTH WITH AN
ASSOCIATED POTENT VORT MAX SWOOPING ON DOWN THROUGH SOUTHERN
CALIFORNIA SATURDAY AFTERNOON. THIS WILL PRODUCE SHOWERS...MAINLY
IN THE HIGH DESERTS...SAN BERNARDINO AND RIVERSIDE COUNTY
MOUNTAINS...AND THE INLAND EMPIRE...ALTHOUGH SOME SHOWER ACTIVITY
COULD LEAK INTO THE LOWER DESERTS...AND THE COAST/VALLEYS OF ORANGE
AND SAN DIEGO COUNTIES AS WELL. SOME MINOR INSTABILITY WITH THE
COLD CORE OF THE LOW COULD LEAD TO SOME LOCALLY HEAVY SHOWERS AND
POSSIBLE THUNDERSTORMS. THE SNOW LEVEL LOOKS TO BE AT AROUND
7500-8000 FEET...AND 1-3 INCHES OF SNOW COULD OCCUR ABOVE THAT
LEVEL. WITH ONSHORE PRESSURE GRADIENTS INCREASING TONIGHT THROUGH
SATURDAY...GUSTY WINDS ARE LIKELY IN THE MOUNTAINS AND DESERTS.
THE WIND FLOW WILL FIRST BE FROM THE WEST TONIGHT/SATURDAY MORNING
AND THEN TURN TO THE NORTH TO NORTHWEST SATURDAY
AFTERNOON/EVENING. GUSTS OF 45-55 MPH WILL BE POSSIBLE IN THOSE
AREAS. FINALLY...WITH THE INCREASING CLOUDS AND COLDER AIR MASS
MOVING IN...HIGHS ON SATURDAY ARE LIKELY TO DROP TO 10-15 DEGREES
BELOW SEASONAL NORMALS.

ALTHOUGH CLOUDS WILL GENERALLY DECREASE ON SUNDAY WITH A LITTLE
BIT OF WARMING AS WELL...A SHORT-WAVE TROUGH AND INCREASED
INSTABILITY COULD LEAD TO A FEW SHOWERS AND POSSIBLY A
THUNDERSTORM OR TWO OVER THE MOUNTAINS AND HIGH DESERTS SUNDAY
AFTERNOON AND EARLY EVENING.

A WARMING AND DRYING TREND IS ON TAP FOR MONDAY THROUGH TUESDAY
WITH RIDGING BUILDING OVER THE REGION. A LARGE TROUGH DROPS DOWN
OFFSHORE STARTING WEDNESDAY...POSSIBLY BRINGING SOME COOLING TO
SOUTHERN CALIFORNIA. THIS TROUGH WILL THEN GRADUALLY MOVE EAST
THURSDAY THROUGH FRIDAY...WITH INCREASING CHANCES FOR
PRECIPITATION FRIDAY AS THE TROUGH AXIS MOVES INLAND OVER
CALIFORNIA. AT THE VERY LEAST...EXPECT CLOUDS AND COOLING TO
INCREASE EACH DAY.

&&

.AVIATION...
291500Z...FROM THE COAST TO COASTAL SLOPES OF MOUNTAINS THERE WILL
BE SCATTERED TO BROKEN CLOUDS 2000-3000 FEET MSL AND TOPS TO 4000
FEET THROUGH 19Z. SCATTERED CLOUDS THROUGH THE DAY. LOW CLOUDS AT
AROUND 1800-2200 FEET MSL WITH TOPS TO ABOUT 3000 FEET WILL DEVELOP
AND GRADUALLY FILL MOST OF THE COASTAL BASIN AFTER 02Z TONIGHT. NOT
MUCH IF ANY CLEARING BEFORE 18Z SATURDAY.

IN THE HIGHER MOUNTAINS AND DESERTS MOSTLY CLEAR SKIES WILL PREVAIL
TODAY AND TONIGHT...EXCEPT FOR SOME AFTERNOON CLOUDS AROUND 8000
FEET OVER THE MOUNTAINS. GUSTY NORTHWEST WINDS WILL DEVELOP THIS
AFTERNOON AND CONTINUE THROUGH SATURDAY LEADING TO POCKETS OF
MODERATE UPDRAFTS AND LOCALIZED LLWS IN LEE OF MOUNTAIN RIDGES.

&&

.MARINE...
800 AM...NORTHWEST WINDS AROUND SAN CLEMENTE ISLAND WILL GUST TO
AROUND 20 KT THIS EVENING AND AGAIN SATURDAY EVENING...APPROACHING
HAZARDOUS CONDITIONS FOR SMALL CRAFT IN THAT AREA. OTHERWISE...NO
MARINE WEATHER HAZARDS ARE EXPECTED THROUGH TUESDAY.

&&

.BEACHES...
800 AM...NORTHWEST SWELL AND AN INCREASING SOUTH SWELL WILL BRING
SURF AS HIGH AS 6 FEET THIS WEEKEND AND SOME STRONG RIP CURRENTS.

&&

.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...HARRISON
AVIATION/MARINE/BEACHES...MM



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