200  
FXUS66 KMTR 270405  
AFDMTR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA  
905 PM PDT WED JUL 26 2017  
   
SYNOPSIS
 
A GRADUAL WARMING TREND WILL GET UNDERWAY THROUGH LATE  
WEEK AND EXTEND INTO NEXT WEEK. AS THE SUB-TROPICAL RIDGE STRENGTHENS  
THIS WEEKEND AND NEXT WEEK OVER MUCH OF THE WEST INCLUDING CALIFORNIA  
TEMPERATURES WILL CLIMB WELL ABOVE LATE JULY AND EARLY AUGUST AVERAGES;  
IT SHOULD BECOME CLEARER WITH TIME AS TO HOW HOT TEMPERATURES MAY GET  
AND WHAT DAYS WILL BE HOTTEST OVER THE BAY AREA AND NORTH CENTRAL  
COAST. THE SUB-TROPICAL RIDGE WILL THEN BECOME MORE FOCUSED OVER THE  
DESERT SOUTHWEST BY THE MIDDLE OF NEXT WEEK. AS A RESULT INCREASING  
UPPER LEVEL SOUTHERLY WINDS MAY BRING REMNANT MID AND HIGH CLOUDS  
AS FAR NORTH AS THE BAY AREA BEGINNING WEDNESDAY NEXT WEEK FROM THEN  
DECAYING TROPICAL CYCLONES MOVING WEST-NORTHWEST OVER THE TROPICAL  
PACIFIC. PLEASE STAY TUNED TO WEATHER UPDATES IN THE DAYS AHEAD.  
 

 
   
DISCUSSION...AS OF 9:05 PM PDT WEDNESDAY
 
PRESENTLY THE MARINE  
LAYER DEPTH VARIES FROM 1,000 FEET AT THE SAN CARLOS SODAR TO  
2,400 FEET AT THE FORT ORD PROFILER. THE BODEGA BAY PROFILER DATA  
IS OLD.  
 
A CLOSED UPPER LEVEL LOW OVER FAR NORTHERN CALIFORNIA WILL MOVE  
ACROSS THE NORTHERN GREAT BASIN TONIGHT INTO THURSDAY. IN ITS WAKE  
WEAK UPPER LEVEL TROUGHING WILL LINGER OVER CALIFORNIA UNTIL THIS  
WEEKEND WHEN THE SUB-TROPICAL RIDGE STRENGTHENS OVER MUCH OF THE  
WEST INCLUDING CALIFORNIA. THE SUB-TROPICAL RIDGE WILL PERSIST  
THROUGH NEXT WEEK TENDING TO TAKE UP RESIDENCE OVER THE DESERT  
SOUTHWEST BY THE MIDDLE OF NEXT WEEK. LARGE SCALE AND INCREASING  
SUBSIDENCE UNDERNEATH THIS RIDGE COINCIDING WITH LONG WAVE RIDGING  
OVER THE WEST WILL PUSH TEMPERATURES UPWARDS, BUT AS TO HOW HOT  
AND WHEN MORE PRECISELY WILL THE HOT WEATHER PEAK IS NOT VERY  
CLEAR YET. AS A RESULT OF THE SUB-TROPICAL RIDGE EVENTUALLY SHIFTING  
TO THE DESERT SOUTHWEST INCREASING UPPER LEVEL SOUTHERLY WINDS MAY  
BRING REMNANT MID AND HIGH CLOUDS AS FAR NORTH AS THE BAY AREA  
BEGINNING WEDNESDAY NEXT WEEK FROM THEN DECAYING TROPICAL CYCLONES  
MOVING WEST-NORTHWEST OVER THE TROPICAL PACIFIC.  
 

 
   
PREV DISCUSSION...AS OF 1:59 PM PDT WEDNESDAY
 
THIS MORNING'S LOW  
CLOUDS HAVE MOSTLY MIXED OUT FOR INLAND AREAS, REVEALING MOSTLY  
CLEAR TO CLEAR SKIES ACROSS THE REGION. TEMPERATURES ARE GENERALLY  
RUNNING WITHIN SEVERAL DEGREES OF WHAT THEY WERE 24 HOURS AGO AT  
THIS TIME. AFTERNOON HIGH TEMPERATURES WILL RANGE FROM THE 60S TO  
PERHAPS AS WARM AS THE LOW 70S ALONG THE COAST, AND UPPER 70S TO  
LOW 90S FOR INLAND AREAS. CAN'T RULE OUT A FEW AREAS THAT REACH  
THE MID/UPPER 90S FOR PARTS OF THE SOUTHERN SALINAS VALLEY,  
PINNACLES NATIONAL PARK, AND INTERIOR MONTEREY COUNTY.  
 
AN UPPER-LEVEL LOW JUST OFF THE NORTHERN CALIFORNIA COAST WILL  
PUSH NORTHEAST OVER THE NEXT DAY AND WEAKEN AS IT CONTINUES INTO  
THE CONTINENT. BY TOMORROW WE'LL SEE 500 MB HEIGHTS NUDGE UPWARD  
BY 2-4 DECAMETERS AS AN UPPER LEVEL RIDGE EXPANDS OVER THE DESERT  
SOUTHWEST. ALONG WITH HEIGHT RISES, MODELS ARE ADVERTISING  
WARMING IN THE LOW AND MID-LEVELS -- 850 MB TEMPS ARE EXPECTED TO  
WARM BY 2-4 DEG C OVER THE NEXT 24 HOURS. AS A RESULT, WE'LL SEE  
WARMING CONDITIONS AT THE SURFACE AND A COMPRESSION OF THE MARINE  
LAYER. THE CHALLENGING ASPECT OF THIS IS HOW WARM WILL WE EXACTLY  
GET FOR THURSDAY AND FRIDAY. LOOKING AT THE MANY ECMWF ENSEMBLE  
MEMBERS, SOME OF THE WARMEST INDIVIDUAL MEMBERS ARE FORECASTING  
THE LOW 90S FOR TOMORROW AT SAN JOSE (KSJC). WITH THIS IN MIND,  
THE OFFICIAL FORECAST FOR THE NEXT FEW DAYS CONTINUES TO FOLLOW  
SOME OF THE WARMEST GUIDANCE. AS FOR THE POTENTIAL HEAT LEVELS,  
THERE ARE SOME AREAS OF MODERATE HEAT RISK FOR THE INTERIOR EAST  
BAY AND PARTS OF THE SOUTH BAY, BUT NOT QUITE ENOUGH COVERAGE TO  
CONSIDER A HEAT ADVISORY. WE'LL CONTINUE TO MONITOR FORECAST HIGHS  
AND HEAT LEVELS OVER THE NEXT FEW DAYS AND MAKE CHANGES IF  
NECESSARY.  
 
FOR THE FIRST HALF OF THE WEEKEND, TEMPERATURES MAY COOL BY  
A FEW DEGREES FOR INTERIOR LOCATIONS AS 500 MB HEIGHTS FALL WITH  
A PASSING SHORTWAVE. MODELS BEGIN TO DISAGREE WITH THE PLACEMENT  
AND STRENGTH OF THE RIDGE ON SUNDAY, THOUGH OVERALL BEGIN TO TREND  
500 MB HEIGHTS BACK UP INTO MONDAY. INTO TUESDAY AND WEDNESDAY  
NEXT WEEK, MODELS CONTINUE TO ADVERTISE THE UPPER-LEVEL RIDGE OVER  
THE SOUTHWESTERN US. THIS EQUATES TO MORE HOT WEATHER FOR  
INTERIOR AREAS AS WE ENTER THE BEGINNING OF AUGUST.  
 

 
   
AVIATION...AS OF 4:55 PM PDT WEDNESDAY
 
FOR THE 00Z TAFS.  
STRATUS IS REACHING BACK TO THE COASTLINE WITH ONSHORE BREEZES.  
VFR CONTINUES AT THE AREA TERMINALS, HOWEVER CIGS RETURN TONIGHT.  
LOWER LEVEL WARMING AND COMPRESSION OF THE MARINE LAYER MAY TEND  
TO LIMIT COVERAGE OF STRATUS TONIGHT AND THURSDAY MORNING  
DECREASING CONFIDENCE IN TIMING CIGS SOMEWHAT. GUSTY W TO NW WINDS  
DIMINISHING THIS EVENING.  
 
VICINITY OF KSFO...VFR WITH GUSTY W TO NW WINDS TIL 04Z THIS EVENING.  
LOW CIGS TONIGHT, BUT TIMING IS LOW CONFIDENCE.  
 
SFO BRIDGE APPROACH...SIMILAR TO KSFO.  
 
MONTEREY BAY TERMINALS...MVFR CIGS REDEVELOPING THIS EVENING, MVFR  
CIGS TONIGHT. VFR RETURNS BY LATE THURSDAY MORNING.  
 

 
   
MARINE...AS OF 1:47 PM PDT WEDNESDAY
 
WINDS WILL GRADUALLY  
INCREASE AND TRANSITION TO WEST AND NORTHWESTERLY ACROSS THE  
WATERS TODAY. MOST SIGNIFICANT INCREASES IN WIND SPEED WILL BE  
NORTH OF POINT REYES. TROPICAL DISTURBANCES IN THE PACIFIC WILL  
GENERATE A LONG PERIOD SOUTHERLY SWELL THAT WILL REACH THE COASTAL  
WATERS BY FRIDAY.  
 

 
   
MTR WATCHES/WARNINGS/ADVISORIES
 
 
.TNGT...SCA...PT ARENA TO PIGEON PT 10-60 NM FROM 9 PM  
SCA...SF BAY UNTIL 11 PM  
 

 
 

 
 
PUBLIC FORECAST: CANEPA/ROWE  
AVIATION: CANEPA  
MARINE: ANNA  
 
VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO  
 
FOLLOW US ON FACEBOOK, TWITTER, AND YOUTUBE AT:  
WWW.FACEBOOK.COM/NWSBAYAREA  
WWW.TWITTER.COM/NWSBAYAREA  
WWW.YOUTUBE.COM/NWSBAYAREA  
 
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