496  
FXUS66 KMTR 240528  
AFDMTR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA  
928 PM PST THU NOV 23 2017  
   
SYNOPSIS
 
DRY AND MILD WEATHER IS FORECAST FROM FRIDAY THROUGH  
MOST OF SATURDAY. RAIN IS EXPECTED TO SPREAD ACROSS THE REGION  
FROM LATE SATURDAY EVENING THROUGH SUNDAY. SCATTERED SHOWERS ON  
SUNDAY NIGHT WILL TAPER OFF AND END BY MIDDAY MONDAY. DRY WEATHER  
IS THEN EXPECTED FOR THE REMAINDER OF NEXT WEEK.  
 

 
   
DISCUSSION...AS OF 9:05 PM PST THURSDAY
 
RADAR SHOWS THAT  
ISOLATED VERY LIGHT SHOWERS HAVE MOSTLY EXITED THE REGION AND  
SHOWER CHANCES FOR THE REMAINDER OF THE EVENING ARE NEGLIGIBLE.  
CONSIDERABLE MID AND HIGH LEVEL CLOUDINESS PERSISTS ACROSS THE  
REGION AND THE AIRMASS REMAINS QUITE WARM FOR THIS TIME OF THE  
YEAR. 8 PM TEMPERATURES WILL STILL IN THE 60S AT MOST LOCATIONS.  
EXPECT MILD OVERNIGHT LOWS TONIGHT.  
 
THE STRONG UPPER LEVEL RIDGE THAT COVERS THE SOUTHWESTERN U.S.  
WEAKENED SLIGHTLY OVER NORTHERN CALIFORNIA TODAY, BUT THE RIDGE  
CONTINUES TO DOMINATE OUR WEATHER BY SUSTAINING A WARM AIRMASS  
OVER OUR REGION. THIS RIDGE IS FORECAST TO REMAIN IN PLACE THROUGH  
THE EARLY PART OF THE WEEKEND AND MAINTAIN DRY WEATHER CONDITIONS  
ACROSS OUR ENTIRE REGION THROUGH SATURDAY AFTERNOON. THE MOISTURE  
PLUME RESPONSIBLE FOR TODAY'S CLOUDS IS FORECAST TO DISSIPATE  
SOMEWHAT BY TOMORROW, SO EXPECT MORE SUN COMPARED TO TODAY,  
ALTHOUGH PERIODS OF HIGH CLOUDS WILL LIKELY PERSIST. DAYTIME  
TEMPERATURES OVER THE NEXT TWO DAYS WILL CONTINUE TO BE ABOUT 7 TO  
12 DEGREES WARMER THAN NORMAL.  
 
A TROUGH IN THE GULF OF ALASKA IS FORECAST TO DIG SOUTH OFFSHORE  
OVER THE NEXT FEW DAYS AND MERGE WITH WET SYSTEM CURRENTLY  
DEVELOPING MUCH FARTHER TO THE SOUTH. THIS MERGED SYSTEM IS THEN  
EXPECTED TO IMPACT OUR REGION WITH WIDESPREAD RAINFALL LATER IN  
THE WEEKEND. THE 00Z GFS DEPICTS A NARROW BAND OF PRECIPITABLE  
WATER IN EXCESS OF 1.5 INCHES ARRIVING ACROSS OUR AREA BY SATURDAY  
NIGHT IN ADVANCE OF THE INCOMING TROUGH AND THE MODELS HAVE BEEN  
TRENDING WETTER WITH THIS SYSTEM. AS FAR AS TIMING IS CONCERNED,  
THE MODEL CONSENSUS INDICATES THAT RAIN WILL BEGIN IN THE NORTH  
BAY BY LATE SATURDAY EVENING, SPREAD ACROSS MOST OF THE REST OF  
THE SF BAY AREA BY MID MORNING SUNDAY, AND REACH THE MONTEREY BAY  
AREA AROUND MIDDAY SUNDAY. RAIN RATES WITH THIS INITIAL FRONTAL  
RAIN BAND WILL BE LIGHT TO MODERATE FOR THE MOST PART, BUT COULD  
BE BRIEFLY HEAVY IN THE COASTAL RANGES, ESPECIALLY ACROSS THE  
NORTH BAY. IT APPEARS THERE WILL BE A BRIEF BREAK IN THE ACTION  
LATE SUNDAY AFTERNOON AND EARLY EVENING BEFORE AN UPPER LOW MOVES  
IN FROM THE NORTHWEST AND TRIGGERS WIDESPREAD SHOWER ACTIVITY ON  
SUNDAY NIGHT. SHOWERS MAY LINGER INTO MONDAY MORNING BUT ARE  
EXPECTED TO END BY MIDDAY MONDAY.  
 
YESTERDAY THE MODELS WERE PREDICTING NO MORE THAN ABOUT A HALF  
INCH OF RAIN IN OUR AREA FROM LATE SATURDAY THROUGH MONDAY  
MORNING. LATEST MODELS ARE FORECASTING AS MUCH AS THREE TIMES THAT  
AMOUNT. RAINFALL TOTALS ARE NOW FORECAST TO RANGE FROM 0.5-1.5  
INCHES IN THE NORTH BAY AND FROM 0.25" TO 1.00" FOR MOST OF THE  
REST OF OUR FORECAST AREA, EXCEPT AS LITTLE AS A TENTH FOR FAR  
SOUTHERN INLAND AREAS.  
 
GUSTY SOUTHERLY WINDS ARE EXPECTED WITH THIS SYSTEM FROM LATE  
SATURDAY THROUGH MIDDAY SUNDAY, WITH LOCAL WIND GUSTS UP TO 35  
MPH POSSIBLE. GUSTY WESTERLY WINDS WILL THEN FOLLOW ON SUNDAY  
NIGHT. WINDS ARE EXPECTED TO REMAIN BELOW ADVISORY LEVELS.  
 
LONGER RANGE MODELS AGREE THAT DRY WEATHER CAN BE EXPECTED FROM  
MIDDAY MONDAY THROUGH THE REMAINDER OF NEXT WEEK.  
 

 
   
AVIATION...AS OF 9:28 PM PST FRIDAY
 
FOR 06Z TAFS. MID AND HIGH  
LEVEL CLOUDS REMAIN OVER THE AREA. WINDS HAVE DECREASED AND  
REMAIN W-NW ACROSS MOST SITES. CIGS ARE EXPECTED TO LOWER LATE  
THIS EVENING AND OVERNIGHT ACROSS THE REGION DOWN TO MVFR/IFR.  
KSTS IS ALREADY SEEING LIFR CIGS WITH OCCASIONAL FOG. CONFIDENCE  
IN TIMING OF DEVELOPMENT AND CLEARING OF MVFR/IFR CIGS IS LOW.  
 
LOW-MODERATE FORECAST CONFIDENCE.  
 
VICINITY OF KSFO...CURRENTLY VFR AND SHOULD REMAIN AS SUCH UNTIL  
LATER TONIGHT. LIGHT NW WINDS TONIGHT EXPECTED TO BE LESS THAN 10  
KT. CURRENT THINKING IS STILL MVFR CIGS ROLLING IN AROUND 08-09Z.  
 
SFO BRIDGE APPROACH...SIMILAR TO KSFO.  
 
MONTEREY BAY TERMINALS...VFR, WITH IFR CIGS POSSIBLE AROUND  
MIDNIGHT AND LASTING INTO THE EARLY MORNING; LOW CONFIDENCE ON  
CIG TIMING. LIGHT WINDS OVERNIGHT AT AROUND 5 KT.  
 

 
   
MARINE...AS OF 08:21 PM PST THURSDAY
 
MODERATE TO OCCASIONALLY  
STRONG NORTHERLY WINDS WILL CONTINUE OVER THE SOUTHERN WATERS  
THROUGH TOMORROW, AND POSSIBLY INTO SATURDAY MORNING. BY SATURDAY  
WINDS WILL INCREASE ACROSS THE COASTAL WATERS AND TURN SOUTHERLY  
AS A LOW PRESSURE SYSTEMS MOVES INTO THE PACIFIC NORTHWEST. THIS  
WILL CAUSE AN INCREASE IN NORTHWEST SWELL LATE SATURDAY NIGHT  
THAT WILL THEN CONTINUE TO BUILD OVER THE WEEKEND. CHANCES OF  
RAIN ALSO RETURN TO THE AREA THIS WEEKEND.  
 

 
   
MTR WATCHES/WARNINGS/ADVISORIES
 
 
.TDAY...SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM  
 

 
 

 
 
PUBLIC FORECAST: DYKEMA  
AVIATION: AS  
MARINE: AS  
 
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