Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 301608
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
908 AM PDT SAT APR 30 2016

.SYNOPSIS...
DRIZZLE AND LIGHT SHOWERS FROM A COASTAL EDDY LIKELY TO DIMINISH
OVER THE COAST AND VALLEYS BY LATE MORNING. A LOW MOVING DOWN OVER
EXTREME SOUTHEAST CALIFORNIA WILL BRING COOLING AND A DEEP MARINE
LAYER WITH A CHANCE OF SHOWERS AND SLIGHT CHANCE OF THUNDERSTORMS
THROUGH SUNDAY...MAINLY DURING THE AFTERNOON AND EVENING HOURS
EACH DAY. A FEW SHOWERS COULD LINGER NEAR THE SAN BERNARDINO
AND RIVERSIDE COUNTY MOUNTAINS ON MONDAY. OTHERWISE...DRY WITH
WARMING FOR MONDAY AND TUESDAY. FOR WEDNESDAY AND THURSDAY...A
SLOW MOVING LOW PRESSURE SYSTEM OVER THE EASTERN PACIFIC WILL
BEGIN A COOLING TREND WITH INCREASING CLOUDS ON THURSDAY. FOR
THURSDAY NIGHT INTO NEXT WEEKEND...THAT LOW PRESSURE SYSTEM WILL
MOVE SLOWLY INLAND BRINGING COOLING...MORE CLOUDS...AND CHANCES
FOR SHOWERS.

&&

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

WATER VAPOR SATELLITE SHOWS AN UPPER LOW OVER DEATH VALLEY...WITH
RADAR SHOWING BANDS OF SHOWERS ROTATING AROUND THE LOW INTO
SOUTHWEST SAN BERNARDINO COUNTY AND WESTERN RIVERSIDE COUNTY.
MEANWHILE...IN THE LOW LEVELS A COASTAL EDDY IS BRINGING INCREASED
DRIZZLE/SHOWER ACTIVITY INTO WESTERN SAN DIEGO COUNTY...RESULTING
IN NUMEROUS REPORTS OF 0.01-0.03 INCHES OF RAIN. THE 12Z MIRAMAR
SOUNDING SHOWS A MARINE LAYER INVERSION AT AROUND 4500 FEET WITH
SOUTHERLY WINDS AT 15-20 KT BELOW THAT LEVEL...AND WEST TO
NORTHWEST WINDS ABOVE. LATE IN THE MORNING...HI-RES MODELS SHOW
ANY DRIZZLE/LIGHT SHOWERS OVER THE COAST AND VALLEYS DISSIPATING
AS THE MARINE LAYER CLOUDS THIN OUT. MEANWHILE...THE UPPER LOW
WILL CONTINUE TO TRACK SOUTH TODAY INTO EXTREME SOUTHEAST
CALIFORNIA...AND THEN EAST INTO ARIZONA THIS EVENING. NORTHERLY
FLOW ON THE WESTERN SIDE OF THE LOW...IN COMBINATION WITH A STRONG
VORT MAX MOVING DOWN INTO THE REGION...WILL CREATE ADDITIONAL
SHOWERS AND POSSIBLE THUNDERSTORMS THIS AFTERNOON INTO THE
EVENING...MAINLY FOR SAN BERNARDINO AND RIVERSIDE COUNTIES...WHICH
IS WHERE THE HI-RES MODELS FOCUS THE PRECIPITATION. HOWEVER...SOME
SHOWERS AND/OR A THUNDERSTORM OR TWO CANNOT BE RULED OUT FOR
PORTIONS OF SAN DIEGO AND ORANGE COUNTIES. PRECIPITATION AMOUNTS
WILL BE HIGHLY VARIABLE DUE TO THE SHOWERY NATURE OF THE
PRECIPITATION...WITH THE HIGHEST AMOUNTS FOCUSED OVER THE SAN
BERNARDINO AND RIVERSIDE COUNTY MOUNTAINS WHERE LOCALLY 0.50-0.75
INCHES COULD FALL. SNOW LEVELS LOOK TO BE AT AROUND 7500-8500
FEET WITH LOCALLY A FEW INCHES OF SNOW POSSIBLE ABOVE THOSE
ELEVATIONS.

MEANWHILE...SOME GUSTY WESTERLY WINDS CONTINUE FOR THE MOUNTAINS
AND DESERTS THIS MORNING DUE TO SOME STRONG ONSHORE SURFACE FLOW
AND WESTERLY WINDS ALOFT. CURRENTLY...LOCAL GUSTS OF 40-50 MPH
ARE BEING REPORTED THROUGH THE PASSES AND ALONG THE DESERT SLOPES.
A WIND ADVISORY CONTINUES THROUGH 2 PM FOR THE SAN DIEGO AND
RIVERSIDE COUNTY MOUNTAINS...SAN GORGONIO PASS...AND SAN DIEGO
COUNTY DESERTS. FINALLY...WITH THE CLOUDY SKIES AND COLDER AIR
MASS MOVING IN...EXPECT HIGHS TO FALL TO 5-15...AND LOCALLY
20...DEGREES BELOW NORMAL TODAY.

FOR SUNDAY...ALTHOUGH THE LOW WILL CONTINUE TO MOVE EAST OVER
ARIZONA/NEW MEXICO...A WEAK WAVE AND DAY-TIME HEATING INDUCED
INSTABILITY COULD CREATE A FEW SHOWERS AND THUNDERSTORMS OVER THE
MOUNTAINS DURING THE AFTERNOON AND EVENING HOURS.
MEANWHILE...INCREASING 500 MB HEIGHTS BEHIND THE DEPARTED TROUGH
SHOULD BRING SOME WARMING TO THE REGION...ALTHOUGH THE DEEP MARINE
LAYER STRATUS THAT IS EXPECTED TO OCCUR OVER THE COAST AND VALLEYS
IN THE MORNING HOURS MAY ONLY PARTIALLY CLEAR DURING THE DAY.

MONDAY AND TUESDAY...UPPER RIDGING WILL BUILD OVER SOUTHERN
CALIFORNIA...WITH WARMING FOR BOTH DAYS AND DRY WEATHER...EXCEPT
FOR POSSIBLY SOME SHOWER ACTIVITY OVER THE MOUNTAINS MONDAY
AFTERNOON. BY TUESDAY...HIGHS LIKELY TO REACH NEAR TO SLIGHTLY
ABOVE NORMAL.

MODELS STILL SHOW A LARGE TROUGH DROPPING DOWN OFFSHORE STARTING
WEDNESDAY...LIKELY BRINGING THE START OF A COOLING TREND TO
SOUTHERN CALIFORNIA. THIS TROUGH WILL THEN GRADUALLY MOVE EAST
THURSDAY...AND THEN MOVE INLAND EITHER LATE THURSDAY OR EARLY
FRIDAY. AS THE TROUGH AXIS MOVES INLAND FRIDAY INTO
SATURDAY...CHANCES FOR PRECIPITATION INCREASE SIGNIFICANTLY. THE
DETERMINISTIC MODEL RUNS AND MODEL ENSEMBLES ARE IN A LITTLE MORE
DISAGREEMENT TODAY IN TERMS OF THE TIMING...AS THE GFS IS MORE
PROGRESSIVE WITH THE SYSTEM...WHILE THE ECMWF IS SLOWER. JUST HOW
MUCH PRECIPITATION WILL OCCUR REMAINS UNCERTAIN. AT THE VERY
LEAST...EXPECT CLOUDS AND COOLING TO INCREASE EACH DAY.

&&

.AVIATION...
301500Z...COAST/VALLEYS...BKN-OVC LOW CLOUDS BASED 015-025 MSL
MERGING WITH HIGHER LAYERS WITH TOPS AROUND 6000 FT MSL. AREAS OF
LIGHT RAIN. ISOLATED THUNDERSTORMS VALLEY AREAS MAINLY THIS
AFTERNOON THROUGH EARLY EVENING FROM ABOUT 30/18Z TIL 01/02Z WITH
TOPS TO NEAR 15000 FEET MSL. RISK OF VISIBILITIES AT KSAN FALLING
BELOW 3SM IN -SHRA IS LOW. CONFIDENCE IN LOW CLOUDS BASES AT KSAN
RISING TO 3000 FT MSL BY MID AFTERNOON TODAY IS MODERATE.

MOUNTAINS/DESERTS...HIGHER TERRAIN BELOW 6000 FEET MSL OBSCURED IN
CLOUDS AND PRECIPITATION. ISOLATED THUNDERSTORMS POSSIBLE THIS
AFTERNOON AND EVENING MAINLY FROM ABOUT 30/18Z TIL ABOUT 01/04Z.
NORTHWEST WINDS 15-25 KT WITH GUSTS TO 45 KT WITH STRONG UP AND
DOWNDRAFTS AND WIND SHEAR. MOUNTAIN WAVE ROTOR ACTIVITY ON THE LEE
SIDE OF THE MOUNTAINS AND LOCALLY INTO THE DESERTS.

&&

.MARINE...
900 AM...NORTHWEST WINDS GUSTING TO AROUND 20 KT NEAR SAN CLEMENTE
ISLAND. SOUTHWEST WINDS 10-15 KT INNERS WATERS WITH A STRONG EDDY
OVER THE COASTAL WATERS.

&&

.BEACHES...
900 AM...LONG PERIOD SOUTHERLY SWELL FOR ELEVATED SURF SOUTHWEST
FACING BEACHES THIS WEEKEND. STRONG RIP CURRENTS ARE LIKELY AND A
BEACH HAZARD STATEMENT IS IN EFFECT THIS WEEKEND. SEE LAXCFWSGX FOR
DETAILS.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...WIND ADVISORY UNTIL 2 PM PDT THIS AFTERNOON FOR RIVERSIDE COUNTY
     MOUNTAINS-SAN DIEGO COUNTY DESERTS-SAN DIEGO COUNTY
     MOUNTAINS-SAN GORGONIO PASS NEAR BANNING.

     BEACH HAZARDS STATEMENT THROUGH SUNDAY EVENING FOR ORANGE COUNTY
     COASTAL AREAS-SAN DIEGO COUNTY COASTAL AREAS.

PZ...NONE.
&&

$$

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



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