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

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000 FXUS66 KMTR 220513 AFDMTR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 1013 PM PDT TUE OCT 21 2014 .SYNOPSIS...DRY WEATHER CONDITIONS AND SEASONABLE TEMPERATURES WILL PERSIST TROUGH WEDNESDAY WITH PRECIPITATION POSSIBLY RETURNING TO THE NORTH BAY ON THURSDAY. RAIN CHANCES WILL THEN INCREASE AND SPREAD SOUTHWARD FRIDAY NIGHT INTO SATURDAY AS AN UPPER LEVEL SYSTEM MOVES THROUGH THE REGION. && .DISCUSSION...AS OF 9:03 PM PDT TUESDAY...HIGH TEMPERATURES TODAY WERE IN THE MID 60S TO THE 70S...AND LOWS WERE IN THE 40S TO THE LOWER 50S. AVERAGE TEMPERATURES TODAY WERE VERY CLOSE TO NORMAL FOR MANY AREAS AROUND THE REGION FOR WHAT IS NOW...IF YOU CAN BELIEVE HOW FAST 2014 IS PASSING US BY...LATE OCTOBER. SUBSTANTIAL CLOUDINESS AS WELL AS PRECIPITATION CONTINUES TO REMAIN WELL NORTHWEST OF THE BAY AREA AND NORTH CENTRAL COAST THIS EVENING. THE MOST RECENT 6-10 DAY OUTLOOK FROM THE NWS CLIMATE PREDICTION CENTER INCREASES THE LONGWAVE TROUGH COUNT FROM 4 TO 5 AROUND THE NORTHERN HEMISPHERE. ONE LONG WAVE TROUGH WILL BE LOCATED OVER THE EASTERN PACIFIC AND EASTERN GULF OF ALASKA MAKING IT FAVORABLE FOR SHORTWAVE TROUGHS TO STRENGTHEN WHEN THEY MOVE EAST THROUGH THE LONG WAVE TROUGH. A DEEP SURFACE LOW IS OVER THE GULF OF ALASKA WITH A SOLID BAND OF CLOUDS STRETCHING WESTWARD BACK TO THE CENTRAL PACIFIC PER IR SATELLITE IMAGERY. AS MENTIONED...DRY WEATHER PREVAILS IN THE BAY AREA AND CENTRAL COAST THIS EVENING WHILE THE LEADING EDGE OF CLOUDS AND PRECIPITATION FOCUSES MOSTLY ON THE PAC NW COAST AND WESTERN CANADA WITH BRIEF PERIODS OF MODERATE TO HEAVIER RAIN EXPECTED TO ENTER NORTHERNMOST CA THROUGH THE REMAINDER OF THE WEEK. FOR OUR COUNTY WARNING AREA CHANCES OF RAIN WILL INCREASE BY THURSDAY AND AGAIN FRIDAY AS A SLOWLY DIMINISHING COLD FRONTAL SYSTEM MOVES IN FROM THE NORTHWEST. SHOWER CHANCES WILL CONTINUE INTO THE WEEKEND...THEN GRADUALLY TAPER OFF. DRIER WEATHER MAY RETURN AS SOON AS SUNDAY AND DRY WEATHER IS EXPECTED AT LEAST MONDAY AND TUESDAY. HOW LONG THE WINDOW OF DRY WEATHER LASTS NEXT WEEK IS A TOUGH QUESTION TO ANSWER. ANOTHER E PAC TROUGH WILL BE APPROACHING THE AREA BY THE MIDDLE OF NEXT WEEK BUT THERE ARE TIMING AND LOCATION DIFFERENCES AMONG THE GLOBAL MODEL SOLUTIONS THUS THERE IS MUCH LOWER FORECAST CONFIDENCE BY THE MIDDLE OF NEXT WEEK. PRESENT FORECAST LOOKS GOOD. NO UPDATES ARE PLANNED. .PREVIOUS WEATHER DISCUSSION...AS OF 01:54 PM PDT TUESDAY...QUIET WEATHER CONDITIONS ALONG WITH NEAR SEASONAL TEMPERATURES WILL PERSIST OVER THE REGION THROUGH WEDNESDAY AS ZONAL FLOW CONTINUES ACROSS THE REGION. MEANWHILE...THE FORECAST MODELS CONTINUE TO INDICATE A DEEPER POOL OF MOISTURE THAT WILL ADVECT INTO THE PACIFIC NORTHWEST/NORTHERN CALIFORNIA DURING THE LATTER HALF OF THE WEEK. WEAK DISTURBANCES ARE ALSO FORECAST TO RIDE ALONG THE MEAN FLOW...INTERACTING WITH THE ABUNDANT MOISTURE TO BRING RAINFALL TO LOCATIONS NORTH OF OUR FORECAST AREA. BY THURSDAY MORNING...THE MODELS SUGGEST THE DEEPER MOISTURE WILL DROP SOUTHWARD OVER THE NORTH BAY AND BRING INCREASED CHANCES FOR RAINFALL. HOWEVER...THERE WILL LIKELY BE A VERY DISTINCT CUT-OFF FROM AREAS THAT WILL RECEIVE RAINFALL AND THOSE THAT WILL REMAIN DRY. AT THIS TIME...THE BEST CHANCE THURSDAY THROUGH FRIDAY WILL STAY NORTH OF THE GOLDEN GATE. WITH THIS...TEMPERATURES WILL BE A BIT COOLER OVER NORTHERN AREAS WHILE INLAND PORTIONS OF THE CENTRAL COAST WILL WARM SLIGHTLY THROUGH FRIDAY. THERE IS GENERAL AGREEMENT WITH THE FORECAST MODELS THAT A MID/UPPER LEVEL TROUGH WILL DEVELOP OFF THE PACIFIC NORTHWEST COAST...PUSHING INLAND FRIDAY NIGHT INTO SATURDAY. THIS WOULD DRIVE A FRONTAL BOUNDARY THROUGH THE FORECAST AREA AND INCREASE CHANCE FOR PRECIPITATION ACROSS THE ENTIRE REGION. WHILE THE MODELS AGREE ON THE TROUGH PUSHING INLAND...THEY CONTINUE TO DIFFER ON THE AMOUNT OF AVAILABLE MOISTURE AS THIS TRANSITION OCCURS. THE LATEST ECMWF KEEPS PRECIPITATION AMOUNTS LIGHT AS SOUTHWEST FLOW DEVELOPS AHEAD OF THE APPROACHING TROUGH...DRYING THE AIRMASS OUT AHEAD OF THE FRONTAL BOUNDARY. FOR NOW...WILL KEEP THE BEST CHANCES FOR PRECIPITATION AND HIGHEST RAINFALL AMOUNTS OVER THE NORTH BAY FRIDAY NIGHT INTO SATURDAY. WILL KEEP A SLIGHT CHANCE OF PRECIPITATION INTO SATURDAY GIVEN TIMING DIFFERENCES WITH THE MODELS AND LIKELIHOOD OF LINGERING MOISTURE ACROSS THE REGION. CONDITIONS DRY OUT SUNDAY AND MONDAY AS THE MID/UPPER LEVEL TROUGH SHIFTS EASTWARD TOWARD THE ROCKIES AND NORTHWEST FLOW DEVELOPS ALOFT. ALSO EXPECTING A SLIGHT WARMING TREND FOR EARLY NEXT WEEK WITH ZONAL FLOW OVER THE REGION. ANOTHER MID/UPPER LEVEL SYSTEM MAY BRING RAIN CHANCES BACK TO THE AREA BY THE MIDDLE OF NEXT WEEK. SOMETHING WE WILL CONTINUE TO MONITOR AS THE FORECAST MODELS COME INTO BETTER AGREEMENT...OR DIVERGE FURTHER. && .AVIATION...
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AS OF 10:13 PM PDT TUESDAY...CLEAR SKIES EXPECTED TO PREVAIL THROUGH TONIGHT WITH A FEW HIGH CLOUDS TRAVERSING THE REGION OVERNIGHT. LIGHT WINDS EXPECTED THROUGH WEDNESDAY MORNING. MODERATE CONFIDENCE. VICINITY OF KSFO...VFR CONDITIONS EXPECTED THROUGH TONIGHT. MODERATE WEST WINDS WILL EASE BECOMING LIGHT OVERNIGHT. MODERATE CONFIDENCE. KSFO BRIDGE APPROACH...SIMILAR AS KSFO. MONTEREY BAY AREA TERMINALS...VFR CONDITIONS EXPECTED THROUGH TONIGHT. LIGHT AND VARIABLE WINDS EXPECTED OVERNIGHT. MODERATE CONFIDENCE.
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&& .MARINE...
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AS OF 8:36 PM PDT TUESDAY...MODERATE NORTHWEST WINDS OVER THE COASTAL WATERS WILL PERSIST AS HIGH PRESSURE BUILDS OVER THE EASTERN PACIFIC. THE STRONGEST WINDS WILL BE NEAR THE COAST SOUTH OF POINT SUR. LARGE MODERATE PERIOD NORTHWEST SWELL WILL CONTINUE TO MOVE THROUGH THE WATERS TODAY BEFORE DECREASING TONIGHT. WINDS WILL SHIFT MORE SOUTHERLY BY TUESDAY AND WEDNESDAY AS LOW PRESSURE MOVES INTO THE PACIFIC NORTHWEST.
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&& .MTR WATCHES/WARNINGS/ADVISORIES...
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.TNGT...SCA...ROUGH BAR ADVISORY FOR SF BAR UNTIL 3 AM SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
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&& $$ PUBLIC FORECAST: CANEPA/RGASS AVIATION/MARINE: CW 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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