Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 302047
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
147 PM PDT SAT APR 30 2016

.SYNOPSIS...
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 UNDER HIGHER
PRESSURE ALOFT. 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 ROTATING OVER EXTREME
SOUTHEAST CALIFORNIA...WITH LATEST RADAR IMAGERY SHOWING THE BULK
OF SHOWER AND THUNDERSTORM ACTIVITY NEAR THE CORE OF THE LOW AND
ON THE EASTERN EDGE...WHILE ONLY A FEW SHOWERS ARE ENTERING THE
HIGH DESERTS AND SAN BERNARDINO COUNTY MOUNTAINS FROM THE NORTH AT
THE MOMENT. EARLIER DRIZZLE/LIGHT SHOWER ACTIVITY OVER THE COAST
AND VALLEYS HAS DIMINISHED AS MARINE LAYER CLOUDS HAVE THINNED
OUT. 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. NORTHERLY FLOW ON THE
WESTERN SIDE OF THE LOW...IN COMBINATION WITH A STRONG VORT MAX
MOVING DOWN INTO THE REGION...MAY CREATE INCREASING SHOWERS AND
POSSIBLY SOME THUNDERSTORMS THIS AFTERNOON INTO THE
EVENING...MAINLY FOR SAN BERNARDINO AND RIVERSIDE COUNTIES...WHICH
IS WHERE THE HI-RES MODELS FOCUS THE PRECIPITATION. HOWEVER...LATEST
HRRR RUN AND CURRENT SPC INSTABILITY ANALYSIS INDICATES THAT ANY
LOCALLY HEAVY SHOWERS OR THUNDERSTORMS ARE LOOKING LESS LIKELY
THAN THEY WERE EARLIER. SOME SHOWERS AND/OR A THUNDERSTORM OR TWO
CANNOT BE RULED OUT FOR PORTIONS OF SAN DIEGO AND ORANGE COUNTIES.
ADDITIONAL 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 0.25-0.50 INCHES COULD FALL. SNOW LEVELS LOOK TO BE
AT AROUND 7500-8500 FEET WITH LOCALLY A COUPLE INCHES OF SNOW
POSSIBLE ABOVE THOSE ELEVATIONS.

MEANWHILE...WINDS OVER THE MOUNTAINS AND DESERTS HAVE BEEN
DECREASING...WITH NOW ONLY SOME GUSTS IN THE 30-40 MPH RANGE.
THUS...THE WIND ADVISORIES WILL BE ALLOWED TO EXPIRE AT 1 PM.
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...
301950Z...COAST/VALLEYS...MAINLY SCT CLOUDS BASED AROUND 3000 FT
MSL WITHIN A FEW MILES OF THE COAST OTHERWISE MAINLY BKN-OVC
LOW CLOUDS BASED 2500-3500 FT MSL LOCALLY MERGING WITH HIGHER
LAYERS WITH TOPS AROUND 6000 FT MSL. ISOLATED SHOWERS OR
THUNDERSTORMS MAINLY VALLEY AREAS NEAR THE MOUNTAINS THIS
AFTERNOON AND EVENING TIL 01/02Z WITH TOPS TO NEAR 15000 FEET MSL.
AFTER 01/04Z THIS EVENING LOW CLOUDS BASED 1500-2500 FEET MSL WITH
TOPS TO NEAR 5000 FT MSL WILL REDEVELOP OVERNIGHT. RISK OF
VISIBILITIES AT KSAN FALLING BELOW 3SM IN FOG OVERNIGHT
IS LOW. CONFIDENCE IN ARRIVAL TIME OF BKN-OVC LOW CLOUDS
AT THE TAF SITES IS LOW-MODERATE.

MOUNTAINS/DESERTS...HIGHER TERRAIN BELOW 6000 FEET MSL OCCASIONALLY
OBSCURED IN CLOUDS AND PRECIPITATION. ISOLATED THUNDERSTORMS
POSSIBLE THIS AFTERNOON AND EVENING MAINLY TIL ABOUT 01/04Z WITH
TOPS TO NEAR 15000 FT MSL. 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...
100 PM...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...
100 PM...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...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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