Issued by NWS San Francisco Bay Area, CA
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000 FXUS66 KMTR 230558 AFDMTR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA 845 PM PST SUN NOV 22 2009 .DISCUSSION...AS OF 8:45 PM PDT SUNDAY...A WEAK FRONT DISSIPATED AS IT SAGGED FROM NORTH TO SOUTH THROUGH OUR REGION LATE LAST NIGHT AND TODAY. THE FRONT BROUGHT WITH IT CONSIDERABLE CLOUDINESS...BUT ONLY LIGHT AMOUNTS OF RAIN TO THE NORTHERN PART OF THE DISTRICT. MEASURABLE RAINFALL WAS CONFINED ALMOST ENTIRELY TO THE NORTH BAY WHERE RAINFALL TOTALS WERE GENERALLY LESS THAN A TENTH OF AN INCH. SOME OF THE WETTER NORTH BAY MOUNTAIN LOCATIONS PICKED UP AS MUCH AS TWO-TENTHS OF AN INCH. ONLY A FEW ISOLATED LOCATIONS SOUTH OF THE GOLDEN GATE MEASURED ANY RAINFALL. SKIES HAVE BEEN GRADUALLY CLEARING SINCE AFTERNOON AS DRIER NORTHWEST FLOW DEVELOPS BEHIND THE WASHED OUT FRONT. PATCHY LATE NIGHT FOG IS POSSIBLE IN THE NORTH BAY VALLEYS AND NEAR THE DELTA. BUT FOG PROBABLY WON`T OCCUR ELSEWHERE. A FORECAST UPDATE WAS COMPLETED EARLIER IN THE EVENING TO REMOVE FOG FROM COASTAL LOCATIONS AND FROM VALLEYS SOUTH OF SAN FRANCISCO. EVENING WATER VAPOR SATELLITE IMAGERY SHOWS AN UPPER RIDGE CENTERED ALONG 130W. THIS RIDGE IS FORECAST TO GRADUALLY SHIFT EASTWARD OVER CA THROUGH MID WEEK. AT THE SAME TIME...SURFACE HIGH PRESSURE WILL DEVELOP OVER THE GREAT BASIN...TURNING THE FLOW OFFSHORE. THE COMBINATION OF A WARMING AIRMASS ALOFT AND LIGHT OFFSHORE FLOW WILL MEAN MOSTLY CLEAR SKIES AND DRY CONDITIONS ACROSS OUR REGION THROUGH THANKSGIVING DAY...ALONG WITH ABOVE NORMAL DAYTIME TEMPERATURES. HIGHS WILL GENERALLY BE IN THE MID TO UPPER 60S...WITH LOWER TO MID 70S IN SOME OF THE WARMER PARTS OF OUR SOUTHERN-MOST COUNTIES. THE MEDIUM RANGE MODELS HAVE CONSISTENTLY INDICATED THAT A WEAK WEATHER SYSTEM WOULD MOVE INTO THE PAC NW AND FAR NORTHERN CALIFORNIA BY LATE ON THANKSGIVING DAY...BUT THERE HAS BEEN DISAGREEMENT ON HOW FAR SOUTH PRECIP WILL EXTEND AND ALSO ON PRECIP TIMING. LATEST MODEL OUTPUT FROM THE GFS (00Z) AND ECMWF (12Z) INDICATE THAT LIGHT RAIN MAY FALL AS FAR SOUTH AS THE NORTH BAY COUNTIES ON THURSDAY EVENING...AND POSSIBLY LATE ON THURSDAY AFTERNOON IF THE 00Z GFS WERE TO VERIFY. POPS IN THE CURRENT FORECAST ARE HELD BELOW 15 PERCENT ACROSS OUR ENTIRE FORECAST AREA RIGHT ON THROUGH THE END OF THE WEEK. BASED ON LATEST MODEL DATA...BELIEVE THERE SHOULD BE AT LEAST A MENTION OF RAIN CHANCES IN THE NORTH BAY ON THURSDAY NIGHT. WILL WAIT FOR THE 00Z ECMWF BEFORE MAKING ANY ADJUSTMENTS TO THE POP AND WEATHER GRIDS IN THE EXTENDED FORECAST. IN ANY CASE...THANKSGIVING WILL ALMOST CERTAINLY BE A DRY DAY ACROSS OUR FORECAST AREA. IF LIGHT RAIN DOES DEVELOP IN THE NORTH BAY ON THURSDAY...IT WILL LIKELY HOLD OFF UNTIL AFTER SUNSET. INDICATIONS ARE THAT ONCE THE WEAK SYSTEM PASSES INLAND LATE NEXT WEEK...A RIDGE OF HIGH PRESSURE WILL REDEVELOP ALONG THE WEST COAST...PRODUCING DRY AND MILD WEATHER NEXT WEEKEND. && .AVIATION...AS OF 10:00 PM PST SUNDAY...SKIES CLEARED OVER THE SFO BAY AREA AS HIGH PRESSURE OVER THE GREAT BASIN BRINGS A DRY NORTHERLY FLOW. THE DRY AIR IS NOT GETTING TO THE MRY BAY AREA. LOW CEILINGS HAVE LINGERED OVER THE SALINAS VALLEY AND MAY AFFECT SNS AND MRY OVERNIGHT. VICINITY OF KSFO...VFR CONDITIONS THROUGH MONDAY. KSFO BRIDGE APPROACH...VFR CONDITIONS THROUGH MONDAY. MONTEREY BAY TERMINALS...LOW CEILINGS IN THE SALINAS VALLEY WILL AFFECT SNS WITH A LOW CEILING BELOW 500 FEET THROUGH EARLY MONDAY MORNING. VISIBILITIES MAY DROP TO 1-3 MILES. THERE IS THE POSSIBILITY OF THE CLOUDS REACHING MRY BY 12Z. FULL CLEARING EXPECTED BY 17-18Z. && .MTR WATCHES/WARNINGS/ADVISORIES... .TNGT...NONE $$ PUBLIC FORECAST: DYKEMA AVIATION/MARINE: W PI NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO
