Area Forecast Discussion
Issued by NWS San Diego, CA

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000 FXUS66 KSGX 301646 AFDSGX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN DIEGO CA 946 AM PDT THU JUL 30 2015 .SYNOPSIS... WARM AND HUMID TODAY WITH ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS OVER THE AREA. FLASH FLOOD WATCH FOR MOUNTAINS/DESERTS/INLAND EMPIRE THROUGH THIS EVENING. DRIER...WITH NEAR NORMAL HIGH TEMPERATURES...THIS WEEKEND INTO EARLY NEXT WEEK AS HIGH PRESSURE BUILDS ALOFT. NIGHT/MORNING LOW CLOUDS ALONG THE COAST AND BREEZY WESTERLY WIND THROUGH MOUNTAIN PASSES AND ALONG DESERT MOUNTAIN SLOPES THROUGH THE PERIOD. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... AT 9 AM PDT...WATER VAPOR SATELLITE IMAGERY DISPLAYED A BROAD UPPER-LEVEL RIDGE STRETCHING FROM THE LOWER MISSISSIPPI VALLEY TO CENTRAL NEVADA...AND A WEAK UPPER-LEVEL LOW AROUND 200 MILES SSW OF SAN DIEGO. THE 30/1200 UTC KNKX SOUNDING DISPLAYED A VERY MOIST AND UNSTABLE PROFILE...WITH A CALCULATED PRECIPITABLE WATER OF 2.02 INCHES AND MOST-UNSTABLE CAPE OF 2030 J/KG. A WEAK UPPER- LEVEL WAVE MOVING ACROSS THE REGION WAS GENERATING LIGHT SHOWERS OVER PORTIONS OF THE SAN BERNARDINO COUNTY MOUNTAINS AND DESERTS. WITH DIURNAL HEATING...CONDITIONS SHOULD COME TOGETHER LATE THIS MORNING THROUGH THIS EVENING TO GENERATE SHOWERS AND THUNDERSTORMS OVER THE REGION...MAINLY OVER THE DESERTS...MOUNTAINS AND THE INLAND EMPIRE. THE 30/1500 UTC HRRR SHOWS SHOWER AND THUNDERSTORM ACTIVITY DEVELOPING OVER THE SAN DIEGO AND RIVERSIDE COUNTY MOUNTAINS AROUND NOON...THEN DEVELOPING OVER PORTIONS OF SW SAN BERNARDINO COUNTY LATER THIS AFTERNOON AS CLOUDS CLEAR THE AREA. THIS WILL LIKELY BE THE CASE GIVEN MODERATE NEGATIVE VORTICITY ADVECTION IN THE WAKE OF THE UPPER-LEVEL WAVE MOVING OUT OF THE AREA THIS MORNING. IF ANY OF THESE STORMS BECOME STATIONARY...OR TRAIN OVER A LOCATION...THERE IS A GOOD POTENTIAL FOR FLASH FLOODING. HOWEVER...MOST STORMS ARE EXPECTED TO MOVE AROUND 15 MPH GIVEN THE MID AND UPPER-LEVEL WINDS. THE FLASH FLOOD WATCH FOR THE MOUNTAINS...DESERTS AND INLAND EMPIRE REMAINS IN EFFECT THROUGH 8 PM PDT THIS EVENING. A WEAK UPPER-LEVEL WAVE MOVING ACROSS THE REGION TONIGHT WILL CREATE THE POSSIBILITY OF AN ISOLATED SHOWER/THUNDERSTORM OVER THE MOUNTAINS AND DESERTS. ON FRIDAY...FLOW WILL SHIFT FROM SE TO MORE SOUTHERLY...ADVECTING DRIER AIR INTO THE REGION. THIS WILL CREATE LESS OF A FLASH FLOOD THREAT AND LOWER THE COVERAGE OF AFTERNOON THUNDERSTORMS COMPARED TO TODAY. MODELS ARE TRENDING DRIER FOR THE WEEKEND INTO EARLY NEXT WEEK AS THE AFOREMENTIONED UPPER-LEVEL RIDGE BUILDS TO THE SE. WILL WAIT FOR THE 12 UTC MODEL RUNS BEFORE CHANGING THE POP FORECAST. HOWEVER...CONFIDENCE IS INCREASING FOR DRY WEATHER FOR THE WEEKEND THROUGH NEXT TUESDAY. THE 30/0600 GFS BRINGS MOISTURE BACK INTO THE AREA NEXT WEDNESDAY...AND GENERATES THUNDERSTORMS OVER THE MOUNTAINS AND DESERTS NEXT WEDNESDAY AND THURSDAY. BUILDING HEIGHTS OVER THE AREA WILL HELP RAISE HIGH TEMPERATURES TO NEAR NORMAL...AND MAINTAIN A SHALLOW MARINE LAYER WITH PATCHY NIGHT/MORNING LOW CLOUDS/FOG ALONG THE COAST AND COASTAL VALLEYS. NORMAL ONSHORE PRESSURE GRADIENTS WILL CREATE BREEZY WESTERLY WINDS THROUGH MOUNTAIN PASSES AND ALONG DESERT MOUNTAIN SLOPES IN THE AFTERNOONS/EVENINGS THROUGH THE PERIOD. && .AVIATION... 301530Z...COAST/VALLEYS...SCT-BKN LOW CLOUDS PERSIST OVER THE COASTAL BASIN AND INLAND IN/NEAR KCRQ WITH BASES NEAR 1500 FT MSL AND TOPS 2000 FT MSL. THE LOW CLOUDS WILL ERODE THE COAST BETWEEN 30/1500-1800Z. THERE IS A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS THROUGH THIS EVENING ACROSS THE ENTIRE REGION...THOUGH THE MOUNTAINS WILL BE FAVORED. HOWEVER...CONFIDENCE ON TIMING IS LOW SO WILL MONITOR FOR VCTS INCLUSION IN THE TAFS. STRATUS WITH SIMILAR BASES AND HEIGHTS AS THIS MORNING WILL PUSH BACK INLAND AFTER 31/0300Z. MTNS/DESERTS...A CHANCE OF SHOWERS AND THUNDERSTORMS EXISTS THROUGH THIS EVENING ACROSS THE MTS AND DESERTS. GREATEST STORM COVERAGE WILL BE AFT 30/2000Z. THUNDERSTORM BASES WILL GENERALLY BE AOA 8000 FT MSL WITH TOPS TO 40000 FT MSL. THE MAIN THREATS FROM THESE STORMS WILL BE BRIEF HEAVY RAIN...LOWERED VIS...AND FREQUENT CLOUD-TO-CLOUD AND CLOUD-TO-GROUND LIGHTNING. && .MARINE... 830 AM...THERE IS A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS OVER THE INNER COASTAL WATERS THROUGH THIS EVENING AS AN UPPER LEVEL DISTURBANCE MOVES OVER THE AREA. OTHERWISE...NO HAZARDOUS MARINE WEATHER IS EXPECTED THROUGH SUNDAY. && .BEACHES... 830 AM...THE ELEVATED SURF WILL SUBSIDE TODAY AS THE SWELL DECLINES TO AROUND 2 FT AT 14-15 SEC...BUT THE RISK OF STRONG RIP CURRENTS AND LIGHTNING CONTINUES THROUGH THE EVENING. THEREFORE THE BEACH HAZARDS STATEMENT WILL CONTINUE THROUGH THIS EVENING. THE SLOW DOWNWARD TREND IN THE SWELL WILL CONTINUE THROUGH THE WEEKEND. && .SKYWARN... SKYWARN ACTIVATION MAY BE REQUESTED LATER TODAY. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...FLASH FLOOD WATCH UNTIL 8 PM PDT THIS EVENING FOR APPLE AND LUCERNE VALLEYS-COACHELLA VALLEY-RIVERSIDE COUNTY MOUNTAINS- SAN BERNARDINO COUNTY MOUNTAINS-SAN BERNARDINO AND RIVERSIDE COUNTY VALLEYS-THE INLAND EMPIRE-SAN DIEGO COUNTY DESERTS-SAN DIEGO COUNTY MOUNTAINS-SAN GORGONIO PASS NEAR BANNING. BEACH HAZARDS STATEMENT UNTIL 8 PM PDT THIS EVENING FOR ORANGE COUNTY COASTAL AREAS-SAN DIEGO COUNTY COASTAL AREAS. PZ...NONE. && $$ PUBLIC...JJT AVIATION/MARINE/BEACHES...TS

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