713  
FXUS66 KMTR 021553  
AFDMTR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA  
853 AM PDT THU JUL 2 2020  
   
SYNOPSIS
 
SEASONAL TEMPERATURES TODAY, FOLLOWED BY  
WARMING THROUGH INDEPENDENCE DAY, WITH MINOR DAY TO DAY CHANGES  
POSSIBLE NEXT WEEK. LIGHT TO MODERATE ONSHORE FLOW WILL PREVAIL  
THROUGH THE PERIOD, ALONG WITH AREAS OF NIGHT AND MORNING COASTAL  
LOW CLOUDS AND FOG.  
 

 
   
DISCUSSION...AS OF 8:50 AM PDT THURSDAY
 
THE MARINE LAYER IS  
EVIDENT ON VISIBLE SATELLITE IMAGERY THIS MORNING ALONG THE COAST  
AND THE INLAND VALLEYS. THE BODEGA BAY PROFILER SUGGESTS A DEPTH  
OF AROUND 2000 FEET WHILE THE FORT ORD PROFILER IS CLOSER TO 2500  
FEET THIS MORNING. NORTHWEST WINDS AND A DRIER AIR MASS ROUNDING  
CAPE MENDOCINO HAVE SCOURED OUT A HOLE IN THE MARINE LAYER FARTHER  
OFFSHORE BUT NO HOLES EXIST IN THE STRATUS ALONG THE IMMEDIATE  
COAST. A SURFACE EDDY IS DRIVING WEAK SOUTHWEST WINDS AND HELPING  
TO REINFORCE THE MARINE LAYER INLAND FROM THE THICKER LAYER TO THE  
SOUTH RATHER THAN THE DRIER AIR FROM THE NORTHWEST. AS SUCH,  
COULD SEE THE LOW CLOUDS LINGER THROUGH THE MID TO LATE MORNING  
FOR MARINE INFLUENCED SITES. NO SIGNIFICANT CONCERNS TODAY WITH  
SOMEWHAT BELOW NORMAL TEMPERATURES (3-11 DEGREES) ACROSS THE  
REGION.  
 
HIGH PRESSURE BUILDS FROM THE DESERT SOUTHWEST OVER THE NEXT FEW  
DAYS AND WILL BRING A WARMING/DRYING TREND WHICH WILL PEAK ON  
SATURDAY (INDEPENDENCE DAY). TEMPERATURES WILL RISE TO BECOME  
SLIGHTLY TO SOMEWHAT ABOVE SEASONABLE CONDITIONS, MAINLY INLAND,  
WHERE AFTERNOON HIGHS WILL BE IN THE MID 80S TO MID 90S, MEANWHILE  
(SAN JOSE, CONCORD, LIVERMORE, SANTA ROSA, NAPA), THE SAN  
FRANCISCO BAY/MONTEREY BAY SHORELINES WILL BE IN THE LOW 70S TO  
LOW 80S. A PERIOD OF NORTH TO NORTHWEST WINDS SATURDAY NIGHT INTO  
SUNDAY MORNING WILL EXACERBATE FIRE WEATHER RISK FOR THE NORTH  
BAY HILLS AND MOUNTAINS. MEANWHILE, LOW HUMIDITY VALUES WILL  
ELEVATE FIRE WEATHER RISK GIVEN THE INCREASE IN THE NUMBER OF FIRE  
WORKS BEING SHOT OFF THIS WEEKEND, ESPECIALLY GIVEN THAT THE LOCAL  
WRF SUGGESTS A COMPRESSION AND SIGNIFICANT WEAKENING OF THE MARINE  
LAYER BY SATURDAY NIGHT. THAT SAID, THE MAIN FIRE RISK WILL BE  
FROM HUMAN RELATED ACTIVITIES THROUGH THE HOLIDAY WEEKEND (RATHER  
THAN FROM THE WEATHER CONDITIONS) SO PLEASE BE MINDFUL OF ANY  
OUTDOOR ACTIVITIES THAT MAY LEAD TO A SPARK THAT COULD IGNITE A  
WILDFIRE.  
 
NO UPDATES PLANNED THIS MORNING. SEE PREVIOUS DISCUSSION FOR MORE  
DETAILS ON THE CURRENT FORECAST.  
 
   
PREVIOUS DISCUSSION...AS OF 3:15 AM PDT THURSDAY
 
A  
RETROGRADING UPPER LEVEL LOW OVER THE PACNW AND BROAD UPPER TROUGH  
COVERING MUCH OF THE WEST COAST CONTINUES TO BE THE LARGE SCALE  
WEATHER FEATURES OF NOTE. THE LOWERING 500 MB HEIGHTS, DECREASING  
N-S GRADIENT AND CONTINUED ONSHORE FLOW ALLOWED FOR A BETTER  
MARINE LAYER PUSH OVERNIGHT. SATELLITE FOG PRODUCT SHOWS SOLID  
STRATUS ALONG THE ENTIRE COASTLINE, UP THE SALINAS VALLEY, IN SAN  
FRANCISCO BAY AND EVEN IN THE NORTH BAY VALLEYS. FORT ORD PROFILER  
PUTS THE DEPTH AT NEAR 2,000 FEET. THE DEEPER MARINE LAYER HAS  
REDUCED CHANCES FOR DENSE FOG, BUT PATCHY FOG AND SOME COASTAL  
DRIZZLE ARE STILL POSSIBLE EARLY THIS MORNING. TODAY'S WEATHER  
WILL BE SIMILAR TO WEDNESDAY WITH INLAND SUNSHINE AND COASTAL  
CLOUDS. TEMPERATURES WILL BE WITH IN A FEW DEGREES OF YESTERDAY OR  
60/70S COAST AND 80/90S INTERIOR.  
 
THE CURRENT FORECAST FOR FRIDAY AND THE UPCOMING HOLIDAY WEEKEND  
REMAIN ON TRACK. THE UPPER TROUGH BEGINS TO LIFT NORTHWARD ON  
FRIDAY AS A RIDGE OF HIGH PRESSURE BUILDS IN FROM THE DESERT  
SOUTHWARD. FRIDAY WILL FEATURE A SLIGHT UPWARD TREND IN  
TEMPERATURES, BUT MORE NOTICEABLE WARMING WILL OCCUR OVER THE  
HOLIDAY WEEKEND. NO MAJOR HEAT RISK CONCERNS WITH THE WARM UP, BUT  
TEMPERATURES AWAY FROM THE COAST WILL BE ABOVE SEASONAL AVERAGES.  
LACK OF STRONG OFFSHORE FLOW OR STRONG NORTHERLY GRADIENTS WILL  
KEEP NIGHT/MORNING LOW CLOUDS IN THE FORECAST AS WELL.  
 
ONE POTENTIAL ITEM OF CONCERN FOR THE UPCOMING HOLIDAY WEEKEND  
WILL BE A VERY DRY AIRMASS MOVING IN OVER THE REGION SATURDAY  
NIGHT/EARLY SUNDAY MORNING. LASTEST LOCAL WRF MODEL DEVELOPS WEAK  
OFFSHORE FLOW AT 2500 FEET WITH LOWERING HUMIDITY 25-35% OVER  
HIGHER TERRAIN. FORTUNATELY, WINDS DO NOT APPEAR TO OVERLY STRONG  
SATURDAY NIGHT. NONETHELESS, DRY AND MILD CONDITIONS IN THE HILLS  
COMBINE WITH POSSIBLE FIREWORKS WILL HEIGHTEN FIRE WEATHER  
CONCERNS.  
 
HIGH PRESSURE RETREATS SOUTHWARD ON MONDAY AS ANOTHER TROUGH  
APPROACHES FROM THE NW. A SLIGHT COOLING TREND DEVELOPS EARLY NEXT  
WEEK. THE LATEST MEDIUM RANGE MODELS KEEP COOLING TREND FOR MUCH  
OF NEXT WEEK WITH NIGHT/MORNING CLOUDS.  
 

 
   
AVIATION...AS OF 04:28 AM PDT THURSDAY
 
FOR 12Z TAFS. SATELLITE  
IMAGERY SHOWS STRATUS REMAINS ALONG THE COAST WITH PATCHY LOW  
CLOUDS AROUND THE SF BAY AREA AND OVER THE MONTEREY BAY. PATCHY  
MVFR/IFR CIGS THIS MORNING ALONG THE COAST AND AROUND THE SF BAY  
THROUGH ABOUT 16Z-17Z WITH LATER CLEARING TIMES AROUND THE  
MONTEREY BAY. SOUTHERLY WINDS ANTICIPATED TO KEEP STRATUS OUT OF  
SJC. S/SW WINDS THIS MORNING AROUND TURNING W/SW THIS AFTERNOON  
AROUND 10-15 KT WITH LOCALLY HIGHER GUSTS POSSIBLE. EXPECTING  
STRATUS TO RETURN TONIGHT.  
 
VICINITY OF KSFO...SOUTHERLY WINDS MAY KEEP CIGS FROM BECOMING BKN  
AROUND THE TERMINAL, THOUGH MVFR CONDITIONS POSSIBLE THROUGH  
ABOUT 16Z-17Z THIS MORNING. LIGHT SOUTHERLY WINDS THIS MORNING  
BECOMING WESTERLY THIS AFTERNOON AROUND 15 KT.  
 
SFO BRIDGE APPROACH...SIMILAR TO KSFO, THOUGH CLOUDS MAY FILL IN  
OVER THE APPROACH WHILE SOUTHERLY WINDS KEEP THE TERMINAL CLEAR.  
 
MONTEREY BAY TERMINALS...MVFR/IFR CIGS THROUGH ABOUT 18Z-20Z. IT  
IS POSSIBLE FOR KMRY TO REMAIN UNDER BKN CONDITIONS ALL DAY,  
THOUGH CONFIDENCE IS LOW. SHOULD CLEARING OCCUR, EXPECT AN EARLY  
RETURN LATE THIS AFTERNOON/EARLY THIS EVENING. LIGHT WINDS THIS  
MORNING BECOMING ONSHORE THIS AFTERNOON AROUND 10-15 KT.  
 

 
   
MARINE...AS OF 08:34 AM PDT THURSDAY
 
MODERATE TO STRONG  
NORTHWEST WINDS WILL CONTINUE OVER THE NORTHERN OUTER WATERS  
TODAY. THESE WINDS WILL GENERATE STEEP FRESH SWELL RESULTING IN  
HAZARDOUS SEAS CONDITIONS, PARTICULARLY FOR SMALLER VESSELS.  
GENERALLY LIGHT TO MODERATE WINDS EXPECTED ELSEWHERE AS HIGH  
PRESSURE WEAKENS OFF THE CALIFORNIA COAST AND A LOW PRESSURE  
SYSTEM DEVELOPS OFF THE PACIFIC NORTHWEST. WINDS WILL BEGIN TO  
SUBSIDE TONIGHT AND TOMORROW, THOUGH LOCALLY BREEZY CONDITIONS  
OVER THE NORTHERN OUTER WATERS WILL PERSIST INTO THE WEEKEND. A  
LONG-PERIOD SOUTHERLY SWELL TRAIN WILL ARRIVE LATE TONIGHT INTO  
TOMORROW. THIS WILL CAUSE OCCASIONAL BREAKING WAVES OVER  
NEARSHORE SHOALS AND STRONG CURRENTS ALONG THE COAST, ESPECIALLY  
NEAR POINTS AND HEADLANDS.  
 

 
   
MTR WATCHES/WARNINGS/ADVISORIES
 
 
.TDAY...SCA...PT ARENA TO PIGEON PT 10-60 NM  
SCA...SF BAY UNTIL 9 AM  
SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM UNTIL 9 AM  
SCA...SF BAY FROM 3 PM  
 

 
 

 
 
PUBLIC FORECAST: DRP/MM  
AVIATION: AS  
MARINE: AS/STR  
 
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