557 FXUS66 KSGX 100537 AFDSGX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN DIEGO CA 940 PM PST WED JAN 9 2013 .SYNOPSIS... A STRONG TROUGH OF LOW PRESSURE WILL BRING A MUCH COLDER AIRMASS INTO SOUTHERN CALIFORNIA THURSDAY. A COLD FRONT WILL BRING SCATTERED SHOWERS TO COASTAL AND VALLEY AREAS...AND SNOW AND BLOWING SNOW IN THE MOUNTAINS. STRONG GUSTY WINDS WILL AFFECT ALL AREAS. MOST OF THE PRECIPITATION WILL END EARLY THURSDAY NIGHT...FOLLOWED BY AN EXTENDED PERIOD OF COLD WEATHER THAT WILL LAST THROUGH EARLY NEXT WEEK. FREEZING TEMPERATURES ARE LIKELY EACH NIGHT IN WIND SHELTERED VALLEY...DESERT AND EVEN SOME COASTAL AREAS. A COUPLE OF DISTURBANCES FROM THE NORTH COULD BRING SOME RAIN AND MOUNTAIN SNOW SUNDAY OR MONDAY. WINDY CONDITIONS ARE EXPECTED AGAIN EARLY NEXT WEEK. WARMER WEATHER SHOULD RETURN BY THE MIDDLE OF NEXT WEEK. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... A SHALLOW MARINE LAYER AT THE COAST EARLIER TODAY BROUGHT A BRIEF PERIOD OF DENSE FOG TO THE BEACHES. THE MARINE LAYER HAS DEEPENED QUICKLY SINCE THEN AND IS AROUND 2500 FEET DEEP AT 9 PM. IT WILL SPREAD INTO THE VALLEYS OVERNIGHT AND CONTINUE TO DEEPEN AHEAD OF THE STRONG TROUGH CURRENTLY OVER CENTRAL CALIFORNIA. THE IR SATELLITE LOOP SHOWS THE CLEARLY DEFINED COLD FRONT OVER THE CENTRAL VALLEY MOVING RAPIDLY SOUTH. BY 6 AM THURSDAY THIS FRONT WILL BE READY TO MOVE ACROSS OUR AREA...WITH THE COLD FRONT STRETCHING FROM THE HIGH DESERTS TO WRIGHTWOOD TO LOS ANGELES AND OUT OVER THE COASTAL WATERS. FROM THERE IT WILL RACE QUICKLY ACROSS SO-CAL THU MORNING. THIS COLD FRONT JUST DOES NOT HAVE A LOT OF MOISTURE FEEDING INTO IT. PRECIPITABLE WATER (PW) VALUES MAX OUT AT ONLY 0.90"...AND THIS WILL LIMIT THE PRECIPITATION POTENTIAL. THE OTHER LIMITING FACTOR IS THE SPEED WITH WHICH THIS COLD FRONT WILL MOVE. BIGGER IMPACTS MAY COME FROM THE WIND. SOUTHWEST WINDS HAVE STARTED INCREASING IN THE SAN BERNARDINO MOUNTAINS THIS EVENING WITH A GUST OF 37 MPH FROM A SPOTTER IN WRIGHTWOOD. THIS LOW-LEVEL SOUTHWEST FLOW WILL DRAW SOME MOISTURE INTO THE SYSTEM OVERNIGHT AND COULD ENHANCE THE OROGRAPHIC PRECIP ON THE SOUTHWEST FACING MTNS SLOPES AHEAD OF THE COLD FRONT. A FEW PLACES MAY SEE A 1/4 TO 1/2 INCH AHEAD OF THE COLD FRONT PASSES. HOWEVER...MOST AREAS WILL RECEIVE LESS THAN THAT WITH TOTALS RANGING FROM JUST A FEW HUNDREDTHS TO UP TO A QUARTER INCH IN THE HEAVIEST SHOWERS. UP IN THE MOUNTAINS A WINTER STORM WARNING IS IN EFFECT FOR THU/THU EVENING...BUT THIS IS MORE FOR THE HIGH WINDS AND THE BLOWING SNOW THAN ACTUAL SNOW TOTALS. THE SNOW LEVELS WILL FALL QUICKLY TO AROUND 3000 BY MIDDAY THU AS 850 MB TEMPS FALL TO -2C BY 10 AM. BY LATE AFTERNOON MOST OF THE MOISTURE WILL HAVE PUSHED SOUTHEAST OF THE SAN BERNARDINO MOUNTAINS AND TOWARD THE RIVERSIDE AND SAN DIEGO COUNTY MOUNTAINS WHERE SNOW SHOWERS WILL LINGER INTO THE AFTERNOON AND EVENING. WHAT THIS STORM MAY LACK IN PRECIP IT WILL MAKE UP FOR WITH STRONG WINDS AND COLD WEATHER. THE AFOREMENTIONED WINDS AT WRIGHTWOOD WILL INCREASE OVERNIGHT AND GENERATE MOUNTAIN WAVES DOWN THE LEE SIDE OF THE RIVERSIDE AND SAN DIEGO COUNTY MOUNTAINS INTO THE LOWER DESERTS. MODEL GUIDANCE FCSTS WINDS OF 50-60 KTS DOWN THE MOUNTAINS SLOPES AND INTO SOME AREAS OF THE COACHELLA VALLEY AND THE BORREGO DESERT. THE MOUNTAIN WAVES WEAKEN LATE IN THE DAY BUT WIDESPREAD WINDY CONDITIONS WILL CONTINUE THROUGH EVENING. COASTAL AND VALLEY AREAS WILL ALSO FEEL THE IMPACTS OF THE STRONG WINDS. WINDS AT THE COAST AFTER COLD FRONTAL PASSAGE WILL BE FROM 20-30 MPH AT TIMES...WITH GUSTING TO 45 MPH. THIS IS QUITE STRONG IN AREAS THAT RARELY SEE WINDS THAT HIGH. DOWNED TREES AND POWER LINES WILL BE A CONCERN IN THESE AREAS. THE WINDS WILL USHER IN A VERY COLD AIRMASS. THE 70 DEGREE TEMPS FROM TODAY WILL NOT BE SEEN FOR SEVERAL DAYS. IN FACT...MOST AREAS WILL NOT EVEN REACH 60 DEGREES THROUGH SUNDAY AND THAT INCLUDES THE LOWER DESERTS. A DEEP COLD TROUGH WILL COVER THE WESTERN US FRI-MON WITH A STRONG RIDGE OVER THE EAST PACIFIC. COLD NORTH-NORTHEAST FLOW BETWEEN THESE TWO SYSTEMS WILL KEEP TEMPS WELL BELOW AVERAGE ALL ACROSS THE SOUTHWEST. OVERNIGHT TEMPS WILL FALL BELOW FREEZING FOR LONG DURATIONS IN SOME OF THE WIND SHELTERED COASTAL...VALLEY AND LOWER DESERT AREAS. WIDESPREAD FROST IS LIKELY. FREEZE WATCHES/WARNINGS MAY BE NEEDED. AGRICULTURAL INTERESTS SHOULD PREPARE FOR SEVERAL NIGHTS OF VERY COLD WEATHER. TEMPERATURES MAY FALL INTO THE LOWER 20S IN SOME OF THE COLDEST VALLEYS. THE ONE SAVING GRACE TO LIMITING A TEMPERATURE FREE FALL EACH NIGHT ARE THE EMBEDDED SHORTWAVES IN THE FAST NORTHERLY FLOW. A STRONG WAVE IS FORECAST TO TRACK DOWN THE COAST AND OVER THE SAN DIEGO COASTAL WATERS SUNDAY INTO SUNDAY NIGHT. THIS FEATURE SHOULD BE ABLE TO DRAW IN ENOUGH MOISTURE FOR CLOUDS AND EVEN SOME LIGHT PRECIPITATION THEN...AND THAT WOULD KEEP OVERNIGHT LOWS ON SUNDAY NIGHT FROM FALLING TOO FAR. STRONG NE WINDS WILL LIKELY FOLLOW THIS LOW MONDAY AND TUESDAY. NEXT WEDNESDAY AND THURSDAY...THE HIGH PRESSURE RIDGE OVER THE EASTERN PACIFIC IS FORECAST TO BUILD EASTWARD INTO CENTRAL CALIFORNIA. THIS WOULD BEGIN TO MODIFY THE AIRMASS TO THE POINT WHERE TEMPERATURES WILL BE AT OR ABOVE AVERAGE FOR THE END OF NEXT WEEK. && .AVIATION... 190530Z...STRATUS WITH BASES 1500-2000 FT MSL WILL CONTINUE TO MOVE INLAND OVERNIGHT. BASES WILL LIFT TO AROUND 2500 FT MSL TOPS WILL LIFT TO 5000-6000 FT MSL AS COLD FRONT APPROACHES. FRONT AND ASSOCIATED SHOWERS ARE EXPECTED TO MOVE THROUGH AROUND 09Z-18Z. LOCAL CIGS DOWN TO 1500 FT MSL AND VSBY 3-5SM POSSIBLE IN HEAVIER SHOWERS. SHOWERS EXPECTED TO TAPER OFF THU AFTERNOON. GUSTY WEST-NORTHWEST WINDS WILL DEVELOP BEHIND THE FRONT. GUSTS TO 30 KT POSSIBLE WEST OF THE MTNS...WITH GUSTS 35-50KT POSSIBLE ALONG THE DESERT SLOPES OF THE MTNS AND INTO THE DESERTS AFTER 18Z. MOUNTAIN WAVES WITH MOD-STG UDDFS...LOW-LEVEL WIND SHEAR...AND ROTOR ACTIVITY POSSIBLE IN THE DESERTS...INCLUDING NEAR KPSP AND KTRM. WINDS WILL GRADUALLY WEAKEN THU EVENING. && .MARINE... GALE FORCE WINDS WITH GUSTS TO 40 KT EXPECTED OVER THE COASTAL WATERS THU MORNING THROUGH LATE THURSDAY NIGHT. BREEZY CONDITIONS AND LARGE COMBINED SEAS WILL CONTINUE INTO FRI AFTERNOON OVER THE INNER WATERS AND EARLY SAT MORNING OVER THE OUTER WATERS. A LARGE SWELL WILL GENERATE HIGH SURF THURSDAY INTO EARLY SAT MORNING. IN ADDITION...SPRING TIDES MAY GENERATE COASTAL FLOODING AND MODERATE OR GREATER BEACH EROSION EACH MORNING THROUGH SATURDAY. SEE MARINE WEATHER MESSAGE AND COASTAL FLOOD ADVISORY PRODUCTS...LAXMWWSGX...LAXCFWSGX FOR FURTHER DETAILS. && .SGX WATCHES/WARNINGS/ADVISORIES... HIGH WIND WARNING FOR DESERT AREAS...MIDNIGHT TONIGHT TO 10 PM THU FOR APPLE/LUCERNE VALLEYS AND 4 AM THU TO 3 AM FRI FOR RIVERSIDE/SAN DIEGO COUNTIES...PLUS MIDNIGHT TONIGHT UNTIL BEGINNING OF WINTER STORM WARNING AT 6 AM IN SAN BERNARDINO COUNTY MTNS...SEE LAXNPWSGX. WINTER WEATHER ADVISORY THU/THU EVENING ABOVE 3000 FT IN APPLE/LUCERNE VALLEYS...SEE LAXWSWSGX. HIGH SURF ADVISORY AND COASTAL FLOOD ADVISORY 5 AM THU TO 11 AM SAT FOR SAN DIEGO/ORANGE COUNTY BEACHES...SEE LAXCFWSGX. GALE WARNING 7 AM THU TO 1 AM FRI FOR OUTER COASTAL WATERS AND 2 PM THU TO 1 AM FRI IN INNER COASTAL WATERS...SEE LAXMWWSGX. SMALL CRAFT ADVISORY 10 AM TO 2 PM THU FOR INNER COASTAL WATERS...SEE LAXMWWSGX. && $$ PUBLIC...MOEDE AVIATION/MARINE...SS