499
FXUS66 KMTR 280541
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
1041 PM PDT WED OCT 27 2021
SYNOPSIS
WARMING AND DRYING TREND CONTINUES INTO FRIDAY. AN
APPROACHING COLD FRONT LATE FRIDAY BRINGS COOLER CONDITIONS OVER
THE WEEKEND, BUT THE AREA LOOKS TO REMAIN DRY. EARLY NEXT WEEK A
FRONTAL SYSTEM BRINGS RAIN CHANCES TO THE BAY AREA, WITH HIGHER
CHANCES IN NORTH BAY.
DISCUSSION...AS OF 09:35 PM PDT WEDNESDAY
SATELLITE NIGHT FOG
PRODUCT SHOWS COASTAL FOG MOVING SOUTHWARD FROM POINT REYES
TOWARDS THE SF PENINSULA. IT HASN'T MADE MUCH INTRUSION OVER LAND
AND NOT EXPECTING MUCH OVERNIGHT. HOWEVER, GIVEN THE MOIST AIRMASS
IN PLACE (DEW PT'S IN THE UPPER 50S), CLEAR SKIES, AND LIGHT
WINDS, EXPECTING SOME PATCHY FOG DEVELOPMENT OVERNIGHT.
TOMORROW LOOKS TO BE THE WARMEST DAY OF THE WEEK WITH MOSTLY CLEAR
SKIES IN THE AFTERNOON AND WARMING OF THE BOUNDARY LAYER AS A
RIDGE MOVES OVER THE WEST COAST. A FEW DEGREES OF WARMING COMPARED
TO TODAY WILL ALLOW MOST OF THE AREA TO REACH THE 70S, WITH SOME
LOW 80S POSSIBLE IN OUR WARMEST INTERIOR SPOTS.
FRIDAY WILL BRING SOME COOLING AS AN APPROACHING SHORTWAVE TROUGH
REACHES THE COASTAL WATERS OF FAR NORTHERN CA. THIS SYSTEM WILL
FORM A CUTOFF LOW THAT WILL TRANSIT THROUGH FAR NORCAL OR OREGON,
MEANING OUR AREA WILL REMAIN DRY, WITH PERHAPS A FEW SPRINKLES IN
THE NORTHERN REACHES OF NORTH BAY. THE MOST APPARENT CHANGES FOR
US WILL BE CLOUDY AND COOL CONDITIONS THROUGH THE WEEKEND.
OUR NEXT REAL RAIN CHANCE ARRIVES MONDAY, WITH AN APPROACHING
FRONTAL BOUNDARY. THERE APPEARS TO BE A GOOD CHANCE THE NORTH BAY
WILL SEE A WETTING RAIN, BUT FARTHER SOUTH, MODEL DISCREPANCIES
GIVE US LESS CONFIDENCE. EURO IS MORE BULLISH THAN THE GFS IN
BRINGING MOISTURE TO THE BAY AREA AND CENTRAL COAST. EITHER WAY,
THIS WILL NOT BE AN AR TYPE EVENT, JUST A PROGRESSIVE FRONTAL
SYSTEM. OFFICIAL FORECAST HAS CHANCE POPS COVERING MOST OF THE
CWA.
MORE RAIN CHANCES TOWARDS THE MIDDLE OF NEXT WEEK, BUT UNCLEAR IF
THE MOISTURE WILL DIP SOUTH TOWARDS THE BAY AREA OR CUT OFF OVER
NORCAL, UNDER MORE ZONAL FLOW. CPC PLACES THE BAY AREA IN A
"LEANING ABOVE" PROBABILITY OF PRECIP CATEGORY FOR THEIR 6-10 AND
8-14 DAY OUTLOOKS. SO EVEN THOUGH NO AR IS ON THE HORIZON, A
WETTER PATTERN MAY BE COMING.
AVIATION...AS OF 10:42 PM PDT WEDNESDAY
FOR THE 06Z TAFS.
EARLY EVENING VISIBLE IMAGERY SHOWS FOG ALONG COASTAL SONOMA
COUNTY TO POINT REYES IN MARIN COUNTY, AND ANOTHER PATCH ALONG SAN
FRANCISCO AND COASTAL SAN MATEO COUNTY; FOG RESULTING IN VLIFR-
IFR IN THESE LOCATIONS, VFR ELSEWHERE. WITH A NEUTRAL SFO-SAC
PRESSURE GRADIENT AND WIND OVER LAND, THE ADVECTION OF FOG WILL
LIKELY REMAIN CONFINED TO THE IMMEDIATE COAST WITH A VERY LOW PROB
OF ONSHORE PUSH REACHING INLAND THIS EVENING, ESPECIALLY WITH
LAND BREEZES DEVELOPING THIS EVENING AND OVERNIGHT.
ONGOING MOIST AIR PER DEW POINT TEMPS IN THE UPPER 50S/60. IT WAS
JUST BELOW THE MAX MOVING AVG PER PRECIPITABLE WATER (PW) ON THE
12Z WED OAKLAND UPPER AIR SOUNDING WITH A LITTLE DRYING ALOFT PER
THE 00Z SOUNDING, THOUGH THE PW IS STILL WELL ABOVE LATE OCT
OAKLAND NORMAL. RADIATIVE COOLING UNDER A CLEAR SKY (AND NAM
FORECASTS VERY WEAK PRESSURE FALLS, ADDITIONAL COOLING) TONIGHT
WILL NARROW TEMP-DEW POINT DEPRESSIONS LIKELY RESULTING IN AREAS
VLIFR-IFR CONDITIONS IN FOG AND LOW CLOUDS TONIGHT AND THURSDAY
MORNING; HREF MODEL LEANING THIS WAY. LATE NIGHT/MORNING COOL AIR
DRAINAGE WINDS ALSO ADDING INTO THE MIX WHICH MAY HELP CLEAR OUT
FOG AND/OR LOW CLOUDS AROUND THE MONTEREY PENINSULA EARLIER THAN
USUAL. OVERALL, COOL AIR DRAINAGE WIND FLOW IS A BIT MORE OF A
WILDCARD TONIGHT/THU MORNING SINCE THE ATMOSPHERE IS ALREADY
FAIRLY MOIST, HAS A FIRM STEP IN THE DIRECTION OF FOG AND/OR LOW
CLOUDS FORMATION OVERNIGHT AND THU MORNING. BY LATE THU MORNING
AND AFTERNOON UNDER MAXIMUM DIURNAL MIXING, WHICH IS GETTING
WEAKER AS WE MOVE INTO THE COOL SEASON, OFFERS BEST CHANCES FOR
VFR RETURNING. FOG/LOW CLOUDS COULD BE STUBBORN TO MIX OUT THU
MORNING.
VICINITY OF KSFO...WATCHING CLOSELY A PATCH OF VLIFR-IFR IN FOG
ALONG THE COAST THAT HAS SLOWLY APPROACHED FROM THE NORTHWEST
THIS AFTERNOON. 5 MIN OBSERVATIONS INITIALLY SHOWING NW WIND, BUT
NOW SHOWING WNW WIND DIRECTION WITH SLIGHT INCREASE IN SPEED.
NORTHERLY WINDS ON THE COAST OVERALL FAVOR THE SOUTHWARD ADVECTION
OF THIS FOG PATCH, BUT WILL MONITOR CLOSELY. MOIST AIR IN PLACE,
CLEAR SKY AND WEAK PRESSURE FALLS TONIGHT SETTING UP FOR LIFR-IFR
CONDITIONS TONIGHT AND THURSDAY MORNING. TEMPO BKN004 07Z-11Z THU,
TO PREVAILING IFR THU MORNING WITH MIX OUT PROCESS NEAR 18Z THU. WNW
WIND GRADUALLY DECREASING TO LIGHT AND VARIABLE TONIGHT AND THU
MORNING, THEN NW TO WNW NEAR 10 KNOTS THU AFTERNOON AND EVENING.
KSFO BRIDGE APPROACH...SIMILAR TO KSFO.
MONTEREY BAY...VFR CURRENTLY, LATE EVENING AND OVERNIGHT FOG
AND/OR LOW CLOUDS /LIFR-IFR/ LIKELY. COOL AIR DRAINAGE WINDS
POSSIBLY STRONG ENOUGH TO MIX OUT FOG AND/OR LOW CLOUDS EARLIER
THAN USUAL ON THU MORNING. OTHERWISE VFR THURSDAY.
MARINE...AS OF 08:40 PM PDT WEDNESDAY
NORTHWEST WINDS WILL
PERSIST INTO TONIGHT. LARGE WEST TO NORTHWEST SWELL REMAINS A
CONCERN THROUGH THIS EVENING EVEN AS WAVE HEIGHTS AND PERIODS
GRADUALLY SUBSIDE. HAZARDOUS SEAS ARE STILL EXPECTED AS A RESULT,
PARTICULARLY FOR SMALLER VESSELS. LARGE BREAKING WAVES WILL ALSO
STILL BE POSSIBLE ACROSS NEARSHORE SHOALS AND AROUND HARBOR
ENTRANCES. SEAS WILL CONTINUE SUBSIDING AS WE GO INTO TOMORROW.
MTR WATCHES/WARNINGS/ADVISORIES
.TNGT...SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM UNTIL 3 AM
SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM UNTIL 11 PM
PUBLIC FORECAST: LORBER
AVIATION: DIAZ
MARINE: CANEPA
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