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

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000 FXUS66 KMTR 210520 AFDMTR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 1020 PM PDT SUN APR 20 2014 .SYNOPSIS...DRY WEATHER WILL CONTINUE THROUGH MONDAY...BUT COOLER WEATHER IS EXPECTED AS ONSHORE FLOW STRENGTHENS. A WEAK STORM SYSTEM WILL IMPACT THE AREA MONDAY NIGHT INTO TUESDAY...BRINGING A CHANCE OF LIGHT RAIN AND COOLER TEMPERATURES. DRY WEATHER AND NEAR NORMAL TEMPERATURES RETURN WEDNESDAY BEFORE RAIN CHANCES RETURN AT THE END OF WEEK. && .DISCUSSION...AS OF 9:00 PM PDT SUNDAY...TEMPERATURES MOVED SHARPLY HIGHER TODAY IN RESPONSE TO STRONG SUBSIDENCE UNDER AN UPPER RIDGE AND REDUCED ONSHORE FLOW. AFTERNOON HIGHS WERE MOSTLY IN THE 70S AND 80S. ONLY AREAS ALONG THE IMMEDIATE COAST REMAINED IN THE 60S. HIGHS TODAY WERE AS MUCH AS 15 DEGREES WARMER THAN YESTERDAY. TODAY WILL BE THE WARMEST DAY OF THE WEEK. SKIES REMAIN MOSTLY CLEAR THIS EVENING WITH VIRTUALLY NO COASTAL STRATUS. ONSHORE PRESSURE GRADIENTS ARE BEGINNING TO INCREASE AND THE FORT ORD PROFILER SHOWS THAT A MARINE INVERSION HAS RECENTLY DEVELOPED AT ABOUT 1000 FEET. SO...LOOK FOR AREAS OF COASTAL LOW CLOUDS AND FOG TO DEVELOP OVERNIGHT AND MOVE LOCALLY INLAND LATE. IN ADDITION...HIGH CLOUDS WILL INCREASE AS A PACIFIC WEATHER SYSTEM APPROACHES. THE MODELS CONTINUE TO FORECAST ONLY SCATTERED LIGHT RAINFALL FROM THIS INCOMING SYSTEM...MAINLY ON MONDAY NIGHT WHEN THE UPPER TROUGH AXIS APPROACHES THE COAST. BASED ON LATEST NAM...EURO...AND CANADIAN MODELS...SHOWER ACTIVITY MAY MAKE IT AS FAR SOUTH AS THE BIG SUR COAST ON MONDAY NIGHT. THEREFORE...A FORECAST UPDATE EARLIER THIS EVENING EXTENDED RAIN CHANCES FARTHER TO THE SOUTH ON MONDAY NIGHT. INDICATIONS ARE THAT RAIN CHANCES WILL QUICKLY DIMINISH ON TUESDAY MORNING AS THE UPPER TROUGH AXIS MOVES INLAND. RAIN TOTALS WITH THIS SYSTEM STILL LOOK TO BE AROUND A TENTH OF AN INCH...AT MOST...IN THE NORTH BAY WITH JUST A FEW HUNDREDTHS OR LESS ELSEWHERE. COOLING WILL BEGIN ON MONDAY AS ONSHORE FLOW STRENGTHENS IN ADVANCE OF THE INCOMING SYSTEM...BUT SOUTHERN INTERIOR SECTIONS OF OUR AREA WILL REMAIN RELATIVELY WARM STILL. MORE SIGNIFICANT AND WIDESPREAD COOLING WILL OCCUR BY TUESDAY AS A MUCH COOLER AIRMASS SWEEPS ACROSS OUR AREA. IN ADDITION...TUESDAY WILL BE A BLUSTERY DAY...ESPECIALLY NEAR THE COAST...AS BRISK NORTHWEST WINDS DEVELOP. GRADUAL WARMING IS FORECAST FOR WEDNESDAY AND THURSDAY AS A FLAT UPPER RIDGE DEVELOPS OVER CENTRAL AND SOUTHERN CA. THE MEDIUM RANGE MODELS HAVE DEFINITELY BEEN TRENDING FASTER WITH THE SYSTEM AT THE END OF THE WEEK. THE GFS...ECMWF...AND GEM MODELS ALL SPREAD RAIN ACROSS MOST OF OUR DISTRICT ON THURSDAY NIGHT AND FRIDAY. BUT RAINFALL INTENSITY VARIES...WITH THE GFS BEING THE WETTEST AND THE ECMWF THE DRIEST. THERE IS ALSO DISAGREEMENT REGARDING A SECOND SYSTEM THAT COMES IN OVER THE WEEKEND. THE ECMWF SWEEPS LIGHT AMOUNTS OF RAIN ACROSS MOST OF OUR AREA ON SATURDAY NIGHT...WHILE THE GFS AND CANADIAN MODELS CONFINE WARM ADVECTION RAIN MAINLY TO THE NORTH BAY ON SUNDAY BEFORE BUILDING IN AN UPPER RIDGE. THEREFORE...CONSIDERABLE UNCERTAINTY EXISTS LATE IN THE EXTENDED FORECAST PERIOD...ALTHOUGH THERE DOES APPEAR TO BE A GOOD CHANCE THAT MOST OF OUR AREA WILL GET WET WITH THAT FIRST SYSTEM ON FRIDAY. && .AVIATION...
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AS OF 10:15 PM PDT SUNDAY...CLEAR SKIES OVER THE AREA THIS EVENING. INVERSION LAYER WILL ALLOW PATCHY LOW CLOUDS TO FORM ALONG THE COAST LATE TONIGHT WHICH MAY IMPACT THE MRY BAY. VICINITY OF KSFO...VFR. KSFO BRIDGE APPROACH...SIMILAR TO KSFO. MONTEREY BAY AREA TERMINALS...IFR CIGS AFTER 12Z.
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&& .MARINE...AS OF 4:30 PM PDT SUNDAY...LARGE NW SWELL HAS ARRIVED WITH BUOYS REPORTING WAVES AS HIGH AS 15 TO 16 FEET WITH 15-16 SECOND INTERVAL. WAVES WILL SLOWLY DECREASE TONIGHT WITH PERIODS AROUND 13 SECONDS. A HIGH SURF ADVISORY IS IN EFFECT UNTIL 5 AM PDT MONDAY. && .MTR WATCHES/WARNINGS/ADVISORIES...
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.TNGT...HIGH SURF ADVISORY...ENTIRE COAST FROM SONOMA COUNTY SOUTH TO MONTEREY COUNTY UNTIL 5 AM SCA...ROUGH BAR ADVISORY FOR SF BAR UNTIL 5 AM
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&& $$ PUBLIC FORECAST: DYKEMA AVIATION/MARINE: W PI VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO FOLLOW US ON FACEBOOK, TWITTER, AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.SANFRANCISCOBAYAREA.GOV WWW.TWITTER.COM/NWSBAYAREA WWW.YOUTUBE.COM/NWSBAYAREA

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