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Displaying AFOS PIL: AFDMTR Received: 2014-11-29 05:01 UTC
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098 FXUS66 KMTR 290501 AFDMTR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 901 PM PST FRI NOV 28 2014 .SYNOPSIS...PERIODS OF RAIN ARE FORECAST FROM TONIGHT THROUGH THE WEEKEND. RAINFALL THROUGH THE WEEKEND WILL MOSTLY BE LIGHT TO MODERATE IN INTENSITY...WITH BRIEF LOCALIZED HEAVY RAIN POSSIBLE. RAIN CHANCES WILL DIMINISH ON MONDAY...BUT THEN A POTENTIALLY STRONGER WEATHER SYSTEM WILL BRING MORE RAIN TO THE REGION FROM MONDAY NIGHT THROUGH EARLY WEDNESDAY. RAIN COULD BE HEAVY ON MONDAY NIGHT AND TUESDAY AND WILL BE ACCOMPANIED BY STRONG AND GUSTY WINDS. && .DISCUSSION...AS OF 9:00 PM PST FRIDAY...RAIN BEGAN TO SPREAD INTO THE NORTH BAY LATE THIS AFTERNOON AND HAS BECOME MORE WIDESPREAD NORTH OF THE GOLDEN GATE THIS EVENING. AMOUNTS THUS FAR HAVE GENERALLY BEEN LESS THAN 0.25"...ALTHOUGH SOME LOCATIONS IN SONOMA COUNTY HAVE PICKED UP BETWEEN 0.25-0.50". 00Z MODELS SHOW THE FRONTAL RAIN BAND REACHING SAN FRANCISCO BY MIDNIGHT TONIGHT AND THEN SLOWLY SAGGING SOUTH THROUGH THE REST OF THE SF BAY AREA LATE TONIGHT...AND POSSIBLY REACHING SANTA CRUZ BY DAYBREAK SATURDAY. RAIN RATES LOOK TO BE MOSTLY LIGHT TO MODERATE...ALTHOUGH THE SONOMA COUNTY AIRPORT HAS ALREADY REPORTED A BRIEF EPISODE OF HEAVY RAIN. THE BEST POTENTIAL FOR HEAVIER RAIN RATES WILL BE LATE TONIGHT INTO EARLY SATURDAY MORNING WHEN A SHORTWAVE TROUGH MOVING IN FROM THE WSW ENHANCES THE FRONTAL BOUNDARY. BASED ON THE 00Z NAM AND 00Z GFS...THIS ENHANCEMENT WILL MOST LIKELY OCCUR ACROSS THE SF PENINSULA AND INTO THE EAST AND SOUTH BAY SOMETIME BETWEEN ABOUT 4:00-8:00 AM SATURDAY. ONCE THIS SHORTWAVE MOVES TO OUR EAST LATE SATURDAY MORNING...THE FRONTAL BOUNDARY IS FORECAST TO STALL OUT ACROSS THE MONTEREY BAY AREA AND WEAKEN RATHER RAPIDLY...RESULTING IN PRECIP TAPERING OFF ON SATURDAY AFTERNOON. THE NEXT SHORTWAVE TROUGH WILL APPROACH FROM THE SOUTHWEST ON SATURDAY NIGHT AND RESULT IN RENEWED RAINFALL LATE SATURDAY NIGHT INTO SUNDAY. THE MODELS ARE ALL OVER THE PLACE AS FAR AS PRECIP INTENSITY AND LOCATION OF HEAVIEST RAINFALL ON SUNDAY. SO FORECAST CONFIDENCE IS LOW ON THE POTENTIAL FOR HYDRO IMPACTS LATER THIS WEEKEND. IN ANY CASE...BOTH THE 00Z NAM AND 00Z GFS SHOW ONLY MODERATE RAINFALL AMOUNTS ON SUNDAY AND SO HYDRO ISSUES SHOULD REMAIN MINOR. WINDS THROUGH THE WEEKEND WILL NOT BE A FACTOR. WINDS WILL INCREASE SOMEWHAT ON SUNDAY...BUT MAINLY OVER THE COASTAL WATERS. WINDS OVER LAND SHOULD REMAIN BELOW ADVISORY LEVELS THROUGH SUNDAY NIGHT. MONDAY CONTINUES TO LOOK LIKE A RELATIVELY DRY DAY AS A SHORTWAVE RIDGE TEMPORARILY BUILDS OVER CA...DOWNSTREAM FROM A DEEP UPPER LOW OFFSHORE. THAT LOW WILL GRADUALLY APPROACH THE CALIFORNIA COAST EARLY NEXT WEEK. IT'S THIS SYSTEM THAT HAS THE POTENTIAL TO PRODUCE THE MOST WIDESPREAD AND HEAVIEST RAINFALL OVER THE NEXT SEVERAL DAYS...AND WILL DEFINITELY BE THE ONE TO PRODUCE THE STRONGEST WINDS. RAIN WILL BEGIN TO SPREAD ACROSS THE AREA ON MONDAY NIGHT...WITH THE BULK OF THE PRECIP EXPECTED TO OCCUR ON TUESDAY AND TUESDAY NIGHT WHEN PERIODS OF HEAVY RAIN ARE POSSIBLE. THUNDERSTORMS MAY ALSO OCCUR DURING THIS TIME FRAME...ALTHOUGH THE MODELS KEEP MOST OF THE SIGNIFICANT INSTABILITY OVER THE COASTAL WATERS. SOUTHERLY WINDS WILL INCREASE ON MONDAY IN ADVANCE OF THE APPROACHING SYSTEM...BUT MAINLY OVER THE COASTAL WATERS. LOCALLY STRONG AND GUSTY WINDS WILL DEVELOP OVER LAND BY LATE MONDAY NIGHT AND ESPECIALLY ON TUESDAY AND TUESDAY EVENING. STRONGEST WINDS WILL BE NEAR THE IMMEDIATE COAST AND IN THE COASTAL HILLS WHERE GUSTS TO 50 MPH ARE POSSIBLE. WIND ADVISORIES MAY BE NEEDED FROM LATE MONDAY NIGHT THROUGH TUESDAY EVENING. THE HAZARDOUS WEATHER OUTLOOK WAS UPDATED THIS EVENING TO DRAW ATTENTION TO THIS PERIOD OF STRONGEST WINDS. SHOWERS WILL CONTINUE INTO WEDNESDAY AS THE UPPER LOW ACCELERATES TO THE NORTHEAST. THE UPPER TROUGH AXIS IS FORECAST TO MOVE INLAND BY LATE WEDNESDAY MORNING AND SO SHOWERS WILL PROBABLY TAPER OFF ON WEDNESDAY AFTERNOON. RAIN TOTALS FOR THIS ENTIRE EVENT...FROM THIS EVENING THROUGH THE MIDDLE OF NEXT WEEK...ARE EXPECTED TO BE IMPRESSIVE...BUT HAVE BEEN DIFFICULT TO PREDICT WITH A GREAT DEAL OF CONFIDENCE DUE TO MODEL INCONSISTENCIES. IN GENERAL...WIDESPREAD RAIN TOTALS OF BETWEEN 1 AND 3 INCHES ARE LIKELY IN MOST URBAN LOCATIONS...WITH 3 TO 5 INCH TOTALS CERTAINLY ATTAINABLE IN THE COASTAL HILLS BY THE MIDDLE OF NEXT WEEK. IF ENHANCED FRONTAL RAIN BANDS STALL IN ANY ONE LOCATION FOR ANY LENGTH OF TIME...LOCALIZED AMOUNTS OF SIX INCHES OR MORE ARE POSSIBLE. ONE FACTOR THAT MAY INHIBIT RAINFALL INTENSITY IN THE COASTAL HILLS EARLY NEXT WEEK IS WIND DIRECTION. BECAUSE THE SURFACE LOW WILL BE APPROACHING FROM ALMOST DUE WEST LATE MONDAY AND MONDAY NIGHT...LOW LEVEL WINDS WILL INITIALLY HAVE AN EASTERLY COMPONENT WHICH WILL MEAN GREATLY REDUCED OROGRAPHIC ENHANCEMENT OF RAINFALL IN THE COASTAL HILLS. LOW LEVEL WINDS WILL EVENTUALLY VEER TO THE SOUTH AND SOUTHWEST...MUCH MORE FAVORABLE DIRECTIONS FOR LIFT ALONG THE COASTAL RANGES...BY LATE TUESDAY AND TUESDAY NIGHT...BUT THEN ONLY ACROSS THE SOUTHERN PART OF THE AREA. && .AVIATION...AS OF 4:00 PM PST FRIDAY...A PACIFIC STORM AND THE ASSOCIATED SURFACE FRONT WILL PUSH ONSHORE FROM N TO S BEGINNING IN THE NORTH BAY FROM THIS EVENING INTO TOMORROW MORNING. THE BIGGEST IMPACT IS LIKELY TO BE EARLY TOMORROW MORNING WITH MVFR CIGS AND VISBYS ACCOMPANYING THE HEAVIEST RAIN. SOUTHERLY WINDS AND WET RUNWAYS LIKELY SATURDAY MORNING. LIGHT RAIN SHOWERS INTO THE AFTERNOON. VICINITY OF KSFO...VFR WITH LIGHT WINDS THROUGH THE EARLY EVENING. FRONT IS FORECAST TO LOWER CIGS TONIGHT WITH SOLID RAIN BY 10-12Z SATURDAY. SOUTH-SOUTHEAST WINDS UP TO 10 KTS. BRIEF GUSTS UP TO 15-20 KT MAY ACCOMPANY WIND FROPA. KSFO BRIDGE APPROACH...SIMILAR TO KSFO. MONTEREY BAY AREA TERMINALS...VFR THIS AFTERNOON/EVENING. MVFR LATE IN THE FORECAST WITH PRECIP DEVELOPING AT OR JUST BEFORE SUNRISE. && .MARINE...AS OF 03:44 PM PST FRIDAY...SOUTHERLY WINDS WILL INCREASE OVER THE COASTAL WATERS TONIGHT AND SATURDAY AS A STORM SYSTEM DEVELOPS OFF THE COAST. WINDS WILL BE GUSTY SATURDAY AND SUNDAY PRODUCING HAZARDOUS CONDITIONS WITH A FRESH STEEP SWELL. THE STORM SYSTEM WILL ALSO BRING PERIODS OF MODERATE TO HEAVY RAIN. UNSETTLED WEATHER IS EXPECTED FOR MUCH OF NEXT WEEK AS MORE STORM SYSTEMS MOVE THROUGH THE REGION. && .MTR WATCHES/WARNINGS/ADVISORIES... .TNGT...NONE. && $$ PUBLIC FORECAST: DYKEMA AVIATION: MM/DRP MARINE: 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