Area Forecast Discussion
Issued by NWS San Diego, CA

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000 FXUS66 KSGX 202039 AFDSGX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN DIEGO CA 140 PM PDT SUN APR 20 2014 .SYNOPSIS... HIGH PRESSURE WILL BRING PREDOMINATELY CLEAR SKIES AND WARMER CONDITIONS THROUGH MONDAY. A SHALLOW MARINE LAYER WILL LINGER ALONG THE COAST THOUGH...MODERATING TEMPERATURES...WITH NIGHT AND MORNING LOW CLOUDS AND FOG POSSIBLE. A TROUGH OF LOW PRESSURE WILL THEN MOVE INLAND ACROSS THE WEST TUESDAY AND EARLY WEDNESDAY...WITH COOLER CONDITIONS...A DEEPER MARINE LAYER...AND STRONG AND GUSTY WEST WINDS IN THE MOUNTAINS AND DESERTS DEVELOPING. A TRANSITORY RIDGE WILL BRING MINOR WARMING AND LIGHTER WINDS FOR THURSDAY. HOWEVER...ANOTHER STRONGER TROUGH WILL MOVE INLAND ACROSS THE WEST FOR FRIDAY NIGHT AND THE WEEKEND...BRINGING THE RETURN OF COOLER CONDITIONS...GUSTY WEST WINDS...AND THE POTENTIAL FOR SOME LIGHT PRECIPITATION. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... WATER VAPOR IMAGERY SHOWS A RELATIVELY FLAT RIDGE OF HIGH PRESSURE OVER SOUTHERN CALIFORNIA THIS AFTERNOON....AS A TROUGH OF LOW PRESSURE CONTINUES TO DIG OVER THE EASTERN PACIFIC. AS A RESULT...SKIES ARE PREDOMINATELY SUNNY THIS AFTERNOON...WITH WARMER CONDITIONS PREVAILING ACROSS THE INLAND AREAS. HOWEVER...VISIBLE IMAGERY DOES SHOW A SHALLOW MARINE LAYER ALREADY PUSHING INTO THE SAN DIEGO COUNTY BEACHES...WITH COASTAL TEMPERATURES RUNNING A FEW DEGREES COOLER THAN THIS TIME YESTERDAY. THESE CONDITIONS WILL MAKE FOR A VERY PLEASANT EVENING ACROSS THE REGION. THE LOCAL WRF SHOWS AN EDDY DEVELOP LATE TONIGHT...SO THINK THE MARINE LAYER WILL LIKELY STAY AROUND A SIMILAR DEPTH AS LAST NIGHT...WITH COASTAL LOW CLOUDS REDEVELOPING OVERNIGHT TONIGHT. OTHERWISE...EXPECT TOMORROW TO BE VERY SIMILAR TO TODAY...AS THIS WEAK RIDGE REMAINS IN PLACE. THE TROUGH OVER THE EASTERN PACIFIC WILL THEN SHIFT INLAND ACROSS THE WEST COAST ON TUESDAY AND EARLY WEDNESDAY...BRING MUCH COOLER CONDITIONS AS WELL AS STRONG AND GUSTY WINDS. DAYTIME TEMPERATURES ACROSS THE INLAND AREAS WILL FALL 8 TO 15 DEGREES FROM MONDAY INTO TUESDAY...FALLING BACK TO AVERAGE OR BELOW AVERAGE FOR THIS TIME OF YEAR. THE MARINE LAYER WILL ALSO DEEPEN IN RESPONSE TO THIS TROUGH...BUT THERE MAY BE ENOUGH COLD AIR ASSOCIATED TO MIX OUT THE LOW CLOUDS AS IT PUSHES INLAND ON TUESDAY. THE LOCAL WRF CONTINUES TO TREND THIS WAY...BUT THEN SHOWS ENOUGH LINGERING MOISTURE THAT SOME LOW CLOUDS MAY REFORM TUESDAY NIGHT. THE OTHER STORY WITH THIS TROUGH WILL BE WITH THE GUSTY WEST WINDS IN THE MOUNTAINS AND DESERTS. ONSHORE PRESSURE GRADIENTS WILL LIKELY INCREASE TO BETWEEN 9 AND 11 MBS BETWEEN SAN DIEGO AND DAGGETT...WITH THE 850 MB AND 30 AGL WINDS INCREASE TO BETWEEN 35 AND 45 KTS ON TUESDAY AFTERNOON. THE LATEST MODELS HAVE BACKED OFF THESE WINDS A BIT...SO WILL HOLD OFF ISSUING A HIGH WIND WATCH...BUT ADVISORIES WILL LIKELY BE NEEDED IF CURRENTLY TRENDS CONTINUE. A TRANSITORY RIDGE WILL THEN BUILD BACK ACROSS THE REGION BRIEFLY ON THURSDAY. THIS WEAK RIDGE WILL BRING SOME MODEST WARMING TO THE INLAND AREAS AND LIGHTER WINDS. HOWEVER...ANOTHER STRONGER AND POTENTIALLY COLDER TROUGH WILL DIG ALONG THE WEST COAST FOR FRIDAY AND THE WEEKEND. AT THIS TIME...THE MODELS ARE STILL VARYING A BIT ON THE STRENGTH AND TIMING...BUT THE 12Z ECMWF AND GFS BOTH CAME IN SPEEDING UP THE TIMING OF THIS TROUGH BY ABOUT 12 HOURS. THEY ARE ALSO BOTH SHOWING THAT SOME LIGHT PRECIPITATION COULD ALSO FALL ALONG AND WEST OF THE MOUNTAINS. THEREFORE...ADDED A SLIGHT CHANCE OF SHOWERS STARTING LATE FRIDAY NIGHT AND CONTINUED THE THREAT THROUGH SATURDAY. AT THIS POINT IN TIME...CONFIDENCE IS STILL NOT HIGH...BUT WITH THE MODELS COMING INTO BETTER ALIGNMENT...IT IS DEFINITELY WORTH A MENTION. THE ONLY THING THAT CAN BE SAID WITH CERTAINTY IS THAT COOLER CONDITIONS WILL DEVELOP ALONG WITH GUSTY WEST WINDS IN THE MOUNTAINS AND DESERTS...STARTING ON FRIDAY. && .AVIATION... 202013Z...COAST/VALLEYS...THROUGH 21/0100 UTC...MOSTLY SKC AND UNRESTRICTED VIS...EXCEPT FOR SOME BKN CLDS 1000-1500 FT MSL WITHIN 3 SM OF THE CENTRAL TO SOUTHERN SAN DIEGO COUNTY COAST. 21/0100-0900 UTC...STRATUS FORMING WITHIN 5-10 SM OF THE COAST...WITH BASES 600-900 FT MSL...TOPS 900-1200 FT MSL...AREAS OF VIS 3-5SM...AND LOCAL VIS AOB 2SM...MAINLY ALONG HIGHER COASTAL TERRAIN. HIGH CONFIDENCE IN OCCURRENCE...MODERATE CONFIDENCE ON TIMING. THESE CONDITIONS CONTINUING THROUGH 21/1500 UTC. CLEARING OF STRATUS 21/1500-1800 UTC. MTNS/DESERTS...FEW-SCT CLDS AOA 10000 FT MSL FORMING OVER THE MTNS THROUGH 21/0000 UTC. OTHERWISE...UNRESTRICTED VIS AND MOSTLY SKC THROUGH MONDAY MORNING. && .MARINE... WEST TO NORTHWEST WINDS WILL STRENGTHEN TUESDAY AS A TROUGH OF LOW PRESSURE MOVES ACROSS CALIFORNIA. THE WINDS PEAK TUESDAY NIGHT WITH GUSTS AROUND 25 KT OVER THE OUTER WATERS...AND GUSTS OF 15 TO LOCALLY 25 KT OVER THE INNER WATERS. THESE WINDS WILL COMBINE WITH A 6-8 FOOT SHORT-PERIOD SWELL TO BRING HAZARDOUS SEAS FOR SMALL CRAFT OVER THE OUTER WATERS...WITH LOW CONFIDENCE IN SMALL CRAFT ADVISORY CONDITIONS FOR THE INNER WATERS. CONDITIONS WILL IMPROVE ON WEDNESDAY. && .SKYWARN... SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS. && .SGX WATCHES/WARNINGS/ADVISORIES...NONE. && $$ PUBLIC...PALMER AVIATION/MARINE...HARRISON

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