Flash Flood Watch 5, NWS San Diego, CA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
815 AM PDT SUN JUL 13 2008

.SYNOPSIS...
MONSOONAL MOISTURE IN WEAKENING NORTHEAST FLOW ALOFT WILL BRING
VARIABLE CLOUDINESS...WITH A CHANCE OF SHOWERS OR THUNDERSTORMS OVER
THE MOUNTAINS AND DESERTS THROUGH THIS EVENING. THERE IS A SLIGHT
CHANCE OF SHOWERS DRIFTING INTO THE INLAND VALLEYS. DRYING FOR
MONDAY AND TUESDAY WILL DECREASE THUNDERSTORM CHANCES. TEMPERATURES
WILL REMAIN NEAR SEASONAL LEVELS.

&&

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

MARINE LAYER DEPTH WAS AROUND 1000 FEET ALONG THE COAST WITH AREAS
OF STRATUS OVER THE COASTAL WATERS AND ALONG THE IMMEDIATE COASTLINE.

ELSEWHERE...A WEAK INVERTED TROUGH REMAINS OVER THE AREA BUT APPEARS
TO BE A LITTLE FURTHER WEST THAN THE ITS POSITION ON SATURDAY.
NORTHEAST FLOW CONTINUES OVER THE NORTHERN DESERT AREAS
SOUTHWESTWARD INTO LA COUNTY WHEREAS A SOUTHWEST FLOW IS APPARENT IN
SATELLITE IMAGERY OVER THE EASTERN PORTION OF OUR CWA FROM NORTHERN
BAJA THROUGH THE COACHELLA VALLEY.

THE 12Z NKX SOUNDING SHOWS THE AIR MASS REMAINS UNSTABLE OVER THE
AREA BUT NOT QUITE AS UNSTABLE AS SATURDAY MORNING. PRECIP WATER IS
LOWER AND THE K INDEX IS NOT QUITE AS HIGH AS SATURDAY MORNING.
LIFTED INDEX IS ABOUT THE SAME. THE MID AND HIGH CLOUDS ARE MORE
BROKEN UP THIS MORNING ALLOWING BETTER SOLAR HEATING SO COULD BE
MORE ACTIVE OVER THE MOUNTAINS AND DESERTS THIS AFTERNOON THAN
SATURDAY AS A RESULT.

12Z NAM CONTINUES TO SHOW A WEAK FLOW OVER THE AREA THROUGH MONDAY
ALTHOUGH THE TREND IS TOWARDS A DECREASE IN THE MID AND HIGH LEVEL
MOISTURE OVER THE AREA. STILL ENOUGH INSTABILITY ON MONDAY FOR
ISOLATED CONVECTION OVER THE MOUNTAINS AND DESERTS ON MONDAY. THE
NAM DOES SHOW A MINOR SHORTWAVE TROUGH BEGINNING TO MOVE INTO THE
PACIFIC NORTHWEST ON TUESDAY WHICH SHOULD BRING A SOUTHWEST FLOW
ALOFT OVER THE AREA TUESDAY AND WEDNESDAY. THIS SHOULD SHUT OFF THE
MOISTURE FROM THE SOUTH AND SOUTHEAST OVER THE AREA RESULTING IN
FURTHER DRYING. THE FLOW ALOFT WOULD ALSO FAVOR A RETURN OF THE
MARINE LAYER WITH STRATUS ALONG THE COAST AND LOCALLY INLAND OVER
THE VALLEY AND MESA AREAS BY MID WEEK.

MEDIUM RANGE MODELS KEEP A SHORTWAVE TROUGH ALONG THE PACIFIC
NORTHWEST COAST INTO THE WEEKEND WITH A DRY SOUTHWEST FLOW ALOFT
OVER THE AREA.

NO UPDATES ARE PLANNED AT THIS TIME.

&&

.AVIATION...
131515Z...PATCHY MARINE LAYER STRATUS EARLY THIS MORNING ALONG THE
CENTRAL SAN DIEGO COUNTY COAST...OTHERWISE JUST AREAS OF MID AND
HIGH LEVEL CLOUDINESS. STRATUS SHOULD MIX OUT BY 17Z.

CONSIDERABLE SUBTROPICAL MOISTURE CONTINUES OVER THE AREA WITH THE
POTENTIAL FOR SHOWERS AND THUNDERSTORMS TO DEVELOP...ESPECIALLY
MOUNTAINS AND NORTHERN DESERTS. POTENTIAL EXISTS FOR ISOLATED
THUNDERSTORMS WITH LOCAL CIGS BELOW FL050 AND TOPS TO FL450 WITH
STRONG UP AND DOWN DRAFTS...BRIEF...STRONG AND GUSTY SURFACE
WINDS...LARGE HAIL...AND VERY HEAVY RAIN.

DUE TO THE CONVECTIVE ACTIVITY AND DEBRIS...THE MARINE LAYER IS
EXPECTED TO REMAIN CHAOTIC TONIGHT. HOWEVER...AREAS OF CIGS WITH
BASES NEAR 800 FT MSL...AND TOPS BELOW FL012 ARE EXPECTED TO
REDEVELOP ALONG THE COAST AFTER 08Z THROUGH 14Z MON. AREAS OF 3-5SM
VIS IN FOG AND HAZE ARE LIKELY AS WELL BETWEEN 10Z AND 17Z MON.

&&

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

&&

PUBLIC...HORTON
AVIATION/MARINE...JAD

NWS ON THE WEB AT WEATHER.GOV/SANDIEGO

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