Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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000 FXUS66 KMTR 020602 AFDMTR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 1102 PM PDT WED APR 1 2015 .SYNOPSIS...AN UPPER LEVEL RIDGE WILL BUILD OVER THE AREA THURSDAY BRINGING DRIER AND SLIGHTLY WARMER WEATHER THROUGH FRIDAY. AN UPPER LEVEL TROUGH WILL BRING INCREASING CLOUDS TO THE AREA SATURDAY WITH A CHANCE OF RAIN MAINLY OVER THE NORTH BAY ON SUNDAY. COOL WEATHER IS EXPECTED FOR NEXT WEEK WITH A SLIGHT CHANCE FOR RAIN AROUND MIDWEEK. && .DISCUSSION...AS OF 9:00 PM PDT WEDNESDAY...AN UPPER LEVEL DISTURBANCE BROUGHT BREEZY CONDITIONS TO THE AREA TODAY. HIGH TEMPERATURES TODAY WERE A FEW DEGREES COOLER THAN YESTERDAY BUT WERE STILL NEAR NORMAL. A COOL AND DRIER AIRMASS WILL SETTLE OVER THE AREA TONIGHT AS AN UPPER LEVEL RIDGE STARTS TO BUILD OFF THE COAST AND SURFACE HIGH DEVELOPS OVER THE GREAT BASIN. WINDS ARE EXPECTED TO DECREASE LATE TONIGHT AND MAY LEAD TO PATCHY FROST IN THE COLDEST WIND- SHELTERED AREAS. THERE WILL STILL BE ENOUGH WINDS IN THE NORTH BAY TO KEEP MOST AREAS IN THE UPPER 30S TO LOW 40S BUT A FEW OF THE WIND-SHELTERED AREAS MAY DROP INTO THE MID 30S AND THERE MAY BE VERY PATCHY FROST IN THE EARLY MORNING HOURS. WINDS IN SOUTHERN MONTEREY AND SAN BENITO COUNTIES ARE EXPECTED TO DECREASE ENOUGH FOR TEMPERATURES TO DROP TO THE LOW 30S IN THE COLDEST SPOTS. GIVEN THAT IT IS NOW APRIL AND THERE MAY BE SOME BUDDING AGRICULTURAL CROPS...A FROST ADVISORY HAS BEEN ISSUED FOR THESE AREAS FROM 3 AM TO 8 AM THURSDAY MORNING. THE UPPER HIGH AND OFFSHORE FLOW WILL LEAD TO SLIGHTLY WARMER TEMPERATURES OVER THE AREA THURSDAY. THE RIDGE FLATTENS OUT ON FRIDAY BUT WEST TO SOUTHWEST FLOW WILL KEEP TEMPERATURES ABOUT THE SAME. AN UPPER LEVEL LOW FROM THE GULF OF ALASKA DROPS INTO THE PACIFIC NORTHWEST COAST SATURDAY AND MOVES INLAND SUNDAY. THE ECMWF NAM AND GFS MODELS SHOW MOST OF THE MOISTURE CONCENTRATED FROM THE NORTH BAY NORTHWARD BUT THE 18Z GFS BROUGHT LIGHT AMOUNTS OF RAIN DOWN TO THE MRY BAY AREA. AS A RESULT THE FORECAST CALLS FOR A CHANCE OF RAIN SHOWERS IN THE NORTH BAY SUNDAY AND A SLIGHT CHANCE OVER THE SFO AND MRY BAY AREAS. TEMPERATURES WILL BE COOLER THIS WEEKEND DUE TO THE INCREASED CLOUDS AND LOWERING 500 MB HEIGHTS. IT IS TOO EARLY TO DETERMINE RAINFALL AMOUNTS BUT THEY WILL NOT BE VERY LARGE. MEDIUM RANGE MODELS DIFFER IN TERMS OF RAIN CHANCES FOR NEXT WEEK. ECMWF INDICATES CHANCE OF RAIN MIDWEEK AND NEXT WEEKEND WHILE GFS HAS CHANCE OF RAIN NEXT WEEKEND ONLY. && .AVIATION...AS OF 10:45 PM PDT WEDNESDAY...A COLD AND DRY UPPER LEVEL TROUGH WILL MOVE EAST REACHING THE GREAT BASIN AFTER MIDNIGHT. PLENTY OF DRYING IS FORECASTED BEHIND THE TROUGH WITHIN THE MID-UPPER LEVELS OF THE ATMOSPHERE TONIGHT WHICH IS MUCH MORE IDEAL FOR SURFACE WIND DE-COUPLING. THE ACV-SFO AND UKI-STS PRESSURE GRADIENTS ARE 7.1 MB AND 2.9 MB RESPECTIVELY BUT DESPITE A STRONG N-S GRADIENT NOT SEEING A WHOLE LOT OF WIND AT KSTS RIGHT NOW...NNW WIND AT 13 KNOTS. OTHER AREA TERMINALS ARE REPORTING LESS WIND. MODERATE TO HIGH CONFIDENCE VFR FOR THE PERIOD. VICINITY OF KSFO...VFR. WESTERLY WINDS HAVE DECREASED APPRECIABLY THROUGH THE EVENING. RECENT OBS SHOW 260 DEGREES AT 8 KNOTS. A WEAKER SFO-SAC GRADIENT IS PREDICTED FOR THURSDAY AFTERNOON PER THE 00Z NAM MODEL...BUT STILL COULD SEE A FEW MID-LATE AFTERNOON W-NW GUSTS APPROACHING 20-22 KNOTS. SFO BRIDGE APPROACH...SIMILAR TO KSFO. MONTEREY BAY AREA TERMINALS...WINDS HAVE SUBSIDED APPRECIABLY THROUGH THE EVENING. VFR. && .MARINE...AS OF 8:33 PM PDT WEDNESDAY...STRONG AND GUSTY NORTHWEST WINDS WILL FOR MUCH OF THE FORECAST. LOCAL GALE FORCE GUSTS WILL BE POSSIBLE...ESPECIALLY THE BIG SUR COAST. THE GUSTY WINDS WILL CAUSE STEEPER WIND WAVES AND HAZARDOUS CONDITIONS. && .MTR WATCHES/WARNINGS/ADVISORIES... .TNGT...FROST ADVISORY...SOUTHERN SALINAS VALLEY AND SAN BENITO COUNTY AND INTERIOR MONTEREY COUNTY. SCA...PIGEON PT TO PT PINOS 0-10 NM UNTIL 5 AM SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM UNTIL 5 AM SCA...PT ARENA TO PT REYES 10-60 NM SCA...PT REYES TO PIGEON PT 10-60 NM SCA...PIGEON PT TO PT PINOS 10-60 NM SCA...PT PINOS TO PT PIEDRAS BLANCAS 10-60 NM SCA...PT ARENA TO PT REYES 0-10 NM SCA...PT REYES TO PIGEON PT 0-10 NM SCA...ROUGH BAR ADVISORY FOR SF BAR UNTIL 3 AM SCA...MONTEREY BAY UNTIL 11 PM && $$ PUBLIC FORECAST: W PI AVIATION: CANEPA MARINE: CANEPA/MM VISIT US AT WEATHER.GOV/SANFRANCISCO FOLLOW US ON FACEBOOK, TWITTER, AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSBAYAREA WWW.TWITTER.COM/NWSBAYAREA WWW.YOUTUBE.COM/NWSBAYAREA

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