FXUS66 KMTR 271301 
  AFDMTR 
   
  AREA FORECAST DISCUSSION 
  NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 
  501 AM PST TUE NOV 27 2012 
   
  ...RAIN AND WIND WEDS MORNING... 
  ...MORE RAIN LATER THURSDAY THROUGH THE WEEKEND... 
   
  .DISCUSSION...AS OF 4:48 AM PST TUESDAY...LOTS ON THE PLATE THIS 
  MORNING SO LETS GET STARTED. 
   
  .SHORT TERM...MUCH LESS FOG THIS MORNING WITH ONLY NAPA AND 
  PETALUMA REPORTING FOG SO FAR THIS MORNING. CLOUD DECKS ARE HIGHER 
  BASED AND ONLY EXPECT SOME PATCHY FOG MAINLY NEAR THE DELTA THIS 
  MORNING. OTHERWISE EXPECT EXTENSIVE MID AND HIGH LEVEL CLOUDS 
  THICKENING AS THE AFTERNOON WEARS ON. CLOUD COVER WILL INHIBIT 
  WARMING AND KEEP TEMPS AROUND 60. 
   
  .TONIGHT...FRONT WILL PUSH INTO THE COASTAL WATERS OVERNIGHT WITH 
  GALE WARNINGS GOING INTO EFFECT. RAIN WILL OVERSPREAD THE OCEAN 
  WATERS IN THE PRE-DAWN HOURS. MODELS HAVE BEEN CONSISTENT IN 
  KEEPING RAIN JUST OFFSHORE UNTIL RIGHT AROUND 12Z WEDS MORNING. 
   
  .WEDS...HAVE ISSUED WIND ADVISORY FOR MOST OF THE DISTRICT EXCEPT 
  FAR SOUTHERN REGIONS WHICH WONT FEEL THE BRUNT OF THE FRONTAL 
  PASSAGE AND ARE SOMEWHAT PROTECTED BY TOPOGRAPHY AS WELL AS THE 
  SANTA CLARA VALLEY. THE SYSTEM IS DYNAMIC AND 925 MB MODEL 
  DEPICTED WINDS CONTINUE TO BE IMPRESSIVE IN THE 50-65 KT RANGE. 
  ACCORDINGLY GALE WARNINGS AND WIND ADVISORIES ARE UP. STRONGEST 
  WINDS EXPECTED ALONG THE COAST AND IN THE HILLS. SANTA CRUZ 
  MOUNTAINS ARE USUALLY SUSCEPTIBLE IN THESE TYPES OF SET UP AS WELL 
  AS THE BIG SUR COAST. WILL LIKELY NEED TO ISSUE AN AIRPORT WEATHER 
  WARNING AS WELL FOR WEDS MORNING WITH STRONG WINDS EXPECTED TO MIX 
  DOWN INTO THE BAY. THE COMBINATION OF WIND AND BRIEF HEAVY RAIN 
  WITH THE FRONTAL PASSAGE SHOULD MAKE THE WEDS MORNING COMMUTE LESS 
  THAN IDEAL. IN ADDITION HAVE ADDED THUNDERSTORM CHANCES FROM 
  12-18Z WEDS WITH THE FRONTAL PASSAGE. LIFTED INDICES ONLY AROUND 
  ZERO BUT BIGGER CONCERN IS STRONG SYNOPTIC LIFT WITH THE SURFACE 
  FRONT ITSELF VERSUS VERY COLD AIR ALOFT. WENT AHEAD AND ADDED 
  POSSIBLE SEVERE WORDING BASED OFF OF LOW LEVEL DIRECTIONAL AND 
  SPEED SHEAR WHICH WILL ONLY BE ENHANCED BY LOCAL TOPOGRAPHY. 
  FORECASTING SEVERE WEATHER AROUND HERE IS NEVER EASY GIVEN HOW 
  RARE IT IS BUT THIS SYSTEM WILL BE DYNAMIC ENOUGH TO SPIN UP SOME 
  MINI-SUPERCELLS. OUR IN-HOUSE LIGHTNING DATA HAS SAMPLED NUMEROUS 
  LIGHTNING STRIKES WELL OFFSHORE WITH THE FRONT...CURRENTLY 
  APPROACHING 130W. IR AND WATER VAPOR SHOW WELL DEFINED SHORTWAVE 
  THAT IS CARVING AND ROUNDING THE BASE OF THE TROUGH. THIS FEATURE 
  WILL BEGIN TO CATCH UP TO SURFACE BOUNDARY AS IT MOVES ONSHORE AND 
  INCREASE THE CHANCES OF CONVECTION. 
   
  GIVEN THE STRONG WINDS ALOFT AND WESTERLY TRAJECTORY...THE FRONTAL 
  PASSAGE WILL BE FAIRLY FAST ON WEDS. THEREFORE WENT WITH THE 
  FAIRLY SHORT WINDOW FOR THE WIND ADVISORY. THE FAST MOVEMENT OF 
  THE FRONT WILL ALSO KEEP EXCESSIVE RAIN POTENTIAL IN CHECK WITH 
  THIS INITIAL FRONTAL PASSAGE. QPF FOR WEDS LOOKS LIKE 0.50-0.75 
  FOR THE LOWER ELEVATIONS AND 1 TO 2 INCHES FOR THE HILLS. STEADY 
  RAIN SHOULD TURN SHOWERY AS EARLY AS THE MIDDAY HOURS OF WEDS. 
   
  .WEDS NIGHT...IN GENERAL A BREAK IN THE WET WEATHER WITH ONLY A 
  FEW SHOWERS EXPECTED AT THIS TIME. 
   
  .THURS...CURRENT FORECAST MAY BE OVERSTATED WITH RAIN CHANCES 
  DURING THE DAY THURSDAY. LATEST MODEL TRENDS NOW SEEM TO SHOW THE 
  NEXT WARM FRONT GETTING IN PLACE NORTH OF THE GOLDEN GATE LATE 
  THURSDAY AFTERNOON OR EVENING. THUS MUCH OF THE DISTRICT AND 
  ESPECIALLY SOUTH OF SAN JOSE COULD REMAIN DRY FOR MUCH OF THURSDAY. 
  THE NEXT WARM FRONTAL SYSTEM IS A CLASSIC SET-UP WHERE HEAVY RAINS 
  CAN FALL IN THE NORTH BAY WHILE A SHARPLY DELINEATED RAIN/NO-RAIN 
  LINE CAN EXIST FOR SEVERAL HOURS. SO LATEST THINKING IS THAT 
  MODERATE RAINS GET CRANKED UP IN THE NORTH BAY THURSDAY EVENING 
  AND THEN ONLY SLOWLY MOVE SOUTHWARD INTO THE BAY AREA ON FRIDAY. 
   
  .FRI...LOOKS WET AS FRONTAL BOUNDARY SLOWLY MOVES THROUGH THE DISTRICT. 
   
  .FRI NIGHT THRU SUNDAY...AFTER A WET AND SOGGY DAY ON FRIDAY RAIN 
  WILL HARDLY HAVE A CHANCE TO END BEFORE NEXT WAVE MOVES ONSHORE. 
  MORE RAIN WILL DEVELOP SATURDAY THROUGH EARLY SUNDAY...HEAVIEST 
  FOR THE NORTH BAY AND SANTA CRUZ MOUNTAINS. FOR THE PERIOD FROM 
  THURSDAY MORNING THROUGH SUNDAY MORNING HERE IS A SAMPLING OF 
  RAINFALL EXPECTED. 6-10 INCHES FOR THE WETTEST NORTH BAY HILLS 
  AND SANTA CRUZ MOUNTAINS. 2-5 INCHES FOR MOST OF THE GREATER BAY 
  AREA WITH LIGHTER AMOUNTS FROM MONTEREY BAY SOUTHWARD. WOULD 
  EXPECT TO SEE SOME WILDLY LARGE RAINFALL TOTALS ACROSS THE 
  DISTRICT BY SUNDAY EVENING. MAIN STEMS DON`T LOOK TO BE A CONCERN 
  AT THIS TIME. HOWEVER CONFIDENCE IS GROWING THAT SOME FAIRLY 
  SIGNIFICANT HYDRO ISSUES WILL DEVELOP OVER THE 3 NORTH BAY 
  COUNTIES AND SANTA CRUZ MOUNTAINS. 
   
  LATEST ECMWF AND GFS DATA SHOWS DRYING TREND BY MONDAY BUT GEM 
  MODEL FOR EXAMPLE KEEPS THINGS WET.  
   
  && 
   
  .AVIATION...AS OF 4:50 AM PST TUESDAY...LOW CIGS COVER THE SFO AND 
  MRY BAY AREA. VSBYS ARE 6 MILES OR GREATER WITH BASES IN MVFR 
  RANGE EXCEPT FOR FOG IN THE NORTH BAY AND IFR CIGS IN THE SOUTH 
  AND EAST BAY VALLEYS. LIGHT WINDS WILL KEEP CIGS IN THE SFO BAY 
  AREA THROUGH AT LEAST 21Z. CIGS COULD STAY IN LONGER POSSIBLY 
  THROUGH THE DAY. SOUTH WINDS INCREASING TO 5-8 KT DURING THE DAY. 
  SOUTH WINDS INCREASING SIGNIFICANTLY AFTER 08Z WEDNESDAY. 
   
  VICINITY OF KSFO...MVFR CIGS THROUGH 21Z AND POSSIBLY LONGER.  
  LIGHT SOUTHERLY WINDS 5-8 KT WILL DEVELOP DURING THE DAY. 
   
  KSFO BRIDGE APPROACH...SIMILAR TO KSFO. 
   
  MONTEREY BAY AREA TERMINALS...MVFR CIGS THROUGH AT LEAST 20Z.  
   
  && 
   
  .HYDROLOGY...AS OF 2:50 PM PST MONDAY...UPDATE TO MENTION A 
  HYDROLOGIC OUTLOOK HAS BEEN ISSUED (SEE SFOESFMTR FOR DETAILS) 
   
  PREVIOUS DISCUSSION...THE PAST SEVERAL STORM SYSTEMS HAVE BROUGHT 
  SIGNIFICANT RAIN TO THE REGION...WITH MANY WATERSHEDS NEARING OR 
  ALREADY ACHIEVING SATURATION. THIS IS PARTICULARLY THE CASE FOR 
  NORTHERN BAY AREA WATERSHEDS...AND EXTENDING SOUTH INTO SAN MATEO 
  COUNTY WATERSHEDS AND NORTHERNMOST SANTA CRUZ COUNTY. STREAM FLOW 
  RECORDS IN MANY LOCATIONS DEPICT ELEVATED BASE FLOW CONDITIONS...A 
  RESULT ACHIEVED BY THE MOST RECENT STORM SYSTEM LAST 
  WEEK...INDICATING THAT THESE BASINS ARE PRIMED TO RESPOND RAPIDLY 
  TO RAIN. 
   
  THE FIRST STORM SYSTEM WILL MOVE INTO THE BAY AREA TUESDAY NIGHT AND  
  INTO WEDNESDAY AND WILL BRING LIGHT TO MODERATE AMOUNTS OF  
  RAINFALL...EXPECT 1 TO 2 INCHES IN HIGHER TERRAIN AND SEVERAL TENTHS  
  TO A HALF INCH IN VALLEY BOTTOMS.  STREAM SYSTEMS ARE LIKELY TO  
  RESPOND RAPIDLY...BUT ARE NOT LIKELY TO REACH ACTION OR FLOOD  
  STAGES.  SATURATED CREEK BANKS FROM RISING WATER LEVELS ALONG WITH  
  MOISTENED SOIL AND WIND GUSTS MAY SERVE TO DELIVER SOME WOODY DEBRIS  
  TO UPLAND AND FORESTED WATERWAYS.  PLAN TO KEEP A DILIGENT EYE ON  
  RAIN GUTTERS...STORM DRAINS...AND CULVERT ENTRANCES AS RACKED DEBRIS  
  WILL CAUSE MORE SERIOUS PROBLEMS WITH THE SECOND SYSTEM PROJECTED TO  
  ARRIVE ON THE HEELS OF THE FIRST. 
   
  A STRONGER SYSTEM IS EXPECTED TO MOVE INTO THE NORTHERN PORTION OF  
  THE BAY AREA BY THURSDAY...BRINGING MORE INTENSE AND PROTRACTED  
  RAINFALL.  MODEL FORECASTS ARE IN GENERAL AGREEMENT THAT UPWARDS OF  
  10 TO 15 INCHES MAY FALL IN HIGHER ELEVATION AREAS OF THE NORTH BAY  
  THROUGH THE WEEKEND...WHILE VALLEY BOTTOMS MAY RECEIVE AROUND 5 TO 6  
  INCHES.  THE SANTA CRUZ MOUNTAINS ARE EXPECTED TO EXPERIENCE SIMILAR  
  CONDITIONS...WHILE MOST OF THE MONTEREY BAY AREA AND SOUTH ARE  
  EXPECTED TO RECEIVE LESS RAIN.  REGARDLESS OF THE  
  SPECIFICS...RAINFALL OF THIS AMOUNT FOLLOWING ON THE HEELS OF THE  
  FIRST SYSTEM WILL CAUSE RAPID RUNOFF AND COULD INDUCE FLOODING OF  
  LOW LYING AREAS AND SMALLER CREEKS AND RIVERS IN THE NORTH BAY AND  
  IN THE SANTA CRUZ MOUNTAINS.  MUDSLIDES ARE ALSO POSSIBLE IN STEEPER  
  TERRAIN.  NONE OF THE MAIN STEM RIVERS ARE EXPECTED TO REACH ACTION  
  OF FLOOD STAGE...BUT THIS CAN QUICKLY CHANGE AS RAIN PATTERNS SHIFT  
  OR INTENSIFY. 
   
  PERSONS LIVING NEAR CREEKS AND RIVERS...OR IN OTHER FLOOD PRONE  
  AREAS...SHOULD BE ALERT FOR THE POSSIBILITY OF FLOODING.  STAY TUNED  
  TO NOAA WEATHER RADIO OR OTHER LOCAL BROADCAST SOURCES OF  
  INFORMATION.  
   
  && 
   
  .MTR WATCHES/WARNINGS/ADVISORIES... 
       .TDAY...SCA...MRY BAY FROM 1 PM 
               SCA...PIGEON PT TO PT PINOS 0-10 NM FROM 1 PM 
               SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM FROM 1 PM 
               SCA...PT REYES TO PIGEON PT 0-10 NM FROM 1 PM 
               SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM FROM 1 PM 
               SCA...PT ARENA TO PT REYES 0-10 NM FROM 9 AM 
               SCA...PT ARENA TO PIGEON PT 10-60 NM FROM 9 AM 
   
  && 
   
  
 
 PUBLIC FORECAST: RWW
 AVIATION/MARINE: W PI
 
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