000 FXUS66 KMTR 300546 AFDMTR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA 1045 PM PDT FRI AUG 29 2008 .DISCUSSION...AS OF 8:00 PM PDT...WIND EVENT LIKELY FOR SUNDAY EVENING THROUGH TUESDAY MORNING ESPECIALLY FOR HIGHER ELEVATIONS. THE SEABREEZE FINALLY KICKED IN ACROSS MANY PORTIONS OF THE DISTRICT TODAY AND TEMPERATURES HAD DROPPED ACCORDINGLY. THE 24 HOUR CHANGE PRODUCT SHOWS MANY SPOTS ARE RUNNING AROUND 10 DEGREES COOLER THAN THIS TIME YESTERDAY. ALL OF THE HEAT RELATED PRODUCTS WERE ALLOWED TO EXPIRE AROUND 6 PM AS EVERYONE DROPS BACK BELOW ADVISORY CRITERIA. SURFACE GRADIENT PATTERN SHOWS THAT THE ONSHORE COMPONENT HAS REALLY STARTED TO RAMP UP AND IS APPROACHING 3 MB. WITH THE FOG PRODUCT SHOWING LOW CLOUDS JUST OFF THE COAST AND IN BOTH BAYS PLUS THE MARINE LAYER BASED OFF THE FORT ORD PROFILER HAS RETURNED AND GONE TO OVER 1000 FEET IN LESS THAN 2 HOURS. ALL SIGNS POINT TO THE RETURN OF PATCHY FOG AND LOW CLOUDS TONIGHT... SOMETHING THAT WE HAVE HAD A NICE BREAK FROM AS OF LATE. THE N-S GRADIENT HAS A VERY ROBUST VALUE OF 5.9 MB FROM THE NORTH WHICH SHOULD BE ENOUGH TO KEEP IT FROM EXTENDED VERY FAR THROUGH SF BAY. THE HOT WEATHER WE HAD TODAY WILL TAKE A BREAK AS THE RIDGE OF HIGH PRESSURE THAT HAD BEEN OVERHEAD MOVES WELL TO THE EAST WHILE A SIGNIFICANT TROUGH MOVES INTO NORTHERN CALIFORNIA AND CONTINUES TO THE GREAT BASIN. ALL OF THE MODELS ARE IN GOOD AGREEMENT WITH THE TIMING...STRENGTH...AND LOCATION OF THE TROUGH SO CONFIDENCE IN THE SUNDAY THROUGH TUESDAY PORTION OF THE FORECAST IS HIGH. WHAT MAKES THIS PARTICULARLY WORTH KEEPING AN EYE ON IS THE ANOMALY CHARTS SHOW STANDARD DEVIATIONS OF BETWEEN -3.5 AND -5 ON BOTH THE 850 MB AND 500 MB CHARTS. IF THE TROUGH IS ABLE TO STRENGTHEN TO A -5 WHEN IT GETS TO THE GREAT BASIN...WE WOULD HAVE A VERY STRONG WIND EVENT ON OUR HANDS ESPECIALLY FROM THE EAST AND NORTH BAY HILLS PLUS THE DIABLO RANGE. THEREFORE...A FIRE WEATHER WATCH WILL BE ISSUED FOR THOSE ZONES. A BIGGER QUESTION MARK IS HOW MUCH OF THE WIND WILL TRANSFER DOWN TO THE SURFACE. ALTHOUGH THE NAM HAS STRONG WINDS AT 925 MB IT DOES NOT BRING MUCH OF THAT DOWN TO THE SURFACE WHICH WOULD SUGGEST THAT THE EVENT MAY BE CONFINED TO HIGHER ELEVATIONS... N-S VALLEYS...AND AREAS PRONE TO DOWNSLOPING FROM THE NORTH. WE WILL LIKELY BE ISSUING WIND ADVISORIES AS THE EVENT GETS CLOSER FOR AT LEAST THE HILLS. BY LATE TUESDAY CALMER CONDITIONS SHOULD RETURN AS THE TROUGH MOVES WELL TO THE EAST WHILE A RIDGE BUILDS ALONG THE COAST. && .FIRE WEATHER...AS OF 8:00 PM PDT FRIDAY...A FIRE WEATHER WATCH IS IN EFFECT FROM SUNDAY EVENING THROUGH TUESDAY MORNING FOR THE NORTH AND EAST BAY HILLS PLUS DIABLO RANGE. FIRE WEATHER CONDITIONS WILL CONTINUE TO IMPROVE THROUGH SUNDAY MORNING AS AN ONSHORE FLOW RETURNS TO THE AREA ALONG WITH HIGHER RELATIVE HUMIDITIES. CONDITIONS ARE EXPECTED TO WORSEN BY SUNDAY AFTERNOON AS A TROUGH MOVES INTO NORTHERN CALIFORNIA SUNDAY EVENING WHICH WILL CAUSE GUSTY SOUTHWESTERLY WINDS IN MANY SPOTS. AT THIS TIME...THIS TROUGH APPEARS TO BE STRONG AND UNUSUALLY FAR TO THE SOUTH FOR THIS TIME OF YEAR WHICH MAKES IT PARTICULARLY CONCERNING GIVEN ALL OF THE FUELS THROUGH OUR AREA. AS THE TROUGH MOVES TO THE GREAT BASIN ON MONDAY...NORTHERLY WINDS WILL STREAM DOWN THE BACK OF IT AND THROUGH CALIFORNIA. EVEN THOUGH TEMPERATURES WILL BE COOLER THAN WHAT WE HAD RECENTLY AND HUMIDITY VALUES WILL BE HIGHER...HIGHER ELEVATION LOCATIONS SUCH AS THE NORTH AND EAST BAY HILLS PLUS DIABLO RANGE WILL LIKELY SEE VERY GUSTY CONDITIONS WHICH SHOULD REACH ADVISORY CRITERIA. THIS WILL CAUSE A DANGEROUS FIRE WEATHER SITUATION THAT WILL LIKELY FACILITATE UPGRADING THE FIRE WEATHER WATCH TO A RED FLAG WARNING AS THE EVENT GETS CLOSER. ALL PERSONS IN THE FIRE COMMUNITY SHOULD CLOSELY MONITOR THE FORECASTS OVER THE NEXT COUPLE OF DAYS. WINDS WILL START TO DIMINISH BY EARLY TUESDAY MORNING AND BE MUCH LIGHTER BY TUESDAY AFTERNOON AS THE TROUGH HEADS WELL TO THE EAST. && .AVIATION...AS OF 10:45 PM PDT FRIDAY...AN APPROACHING UPPER LEVEL TROUGH IS TRIGGERING A RAPID DEEPENING OF THE MARINE LAYER THIS EVENING AS WELL AS INCREASING ONSHORE FLOW. IFR CIGS HAD ALREADY DEVELOPED AT KMRY BY 04Z AND SHOULD DEVELOP AT KSFO AND KOAK BY 09Z. CLEARING AT KSFO ON SATURDAY MORNING IS A DIFFICULT CALL. THE SFO- SAC GRADIENT IS TRENDING STRONGER ONSHORE AND THE MARINE LAYER SHOULD CONTINUE TO DEEPEN OVERNIGHT. THESE FACTORS POINT TO RELATIVELY LATE CLEARING ON SATURDAY...NOT UNTIL 18Z OR LATER. HOWEVER...THE N-S GRADIENT IS INCREASING AND THIS MAY RESULT IN EARLIER CLEARING THAN EXPECTED. BEST ESTIMATE OF CLEARING AT KSFO ON SATURDAY IS 18Z. && .CLIMATE...HERE ARE SELECTED HIGH TEMPERATURES DURING OUR RECENT HEATWAVE. .CITY....................AUG 27....AUG 28...AUG 29 SANTA ROSA................99.......101.......98 PETALUMA.................102.......107......103 SAN FRANCISCO CITY........83........80.......81 CONCORD...................98.......102......103 LIVERMORE................102.......104.......89 LOS GATOS.................99.......103......102 SAN JOSE..................95.......101.......98 MORGAN HILL...............98.......102......103 HOLLISTER.................97........98.......99 PINNACLES................105.......112......113 OAKLAND DOWNTOWN..........88........88.......85 && .MTR WATCHES/WARNINGS/ADVISORIES... .TNGT..SCA.....PT ARENA TO PIGEON PT 20-60 NM...PT ARENA TO PT REYES OUT 20 NM...AND SF BAY. .FIRE WEATHER WATCH FOR THE NORTH BAY AND EAST BAY HILLS (ZONES 507 AND 511) SUNDAY EVENING THROUGH TUESDAY MORNING. $$ PUBLIC FORECAST: BELL AVIATION/MARINE: DYKEMA FIRE WEATHER: BELL CLIMATE: JOROS/BELL NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO