626
FXUS66 KMTR 191827
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1027 AM PST THU DEC 19 2024
..NEW AVIATION
SYNOPSIS
ISSUED AT 929 AM PST THU DEC 19 2024
ONE MORE DAY OF ABOVE NORMAL TEMPERATURES FOR MOST OF OUR
INTERIOR LOCATIONS BEFORE THE FIRST OF NUMEROUS DISTURBANCES
APPROACHES OUR AREA LATE FRIDAY NIGHT INTO EARLY SATURDAY MORNING.
UPDATE
ISSUED AT 917 AM PST THU DEC 19 2024
LOW STRATUS CONTINUES ACROSS THE NORTH BAY VALLEYS AND THE
INTERIOR EAST BAY, PARTIALLY FROM ADVECTION OF LOW STRATUS ALONG
THE DELTA, BUT WITH REPORTED VISIBILITIES INCREASING ACROSS THE
REGION, THE DENSE FOG ADVISORY WAS JUST CANCELLED. MAIN FOCUS OF
THE FORECAST CONTINUES TO BE THE MULTIPLE ROUNDS OF RAIN AND HIGH
SURF EXPECTED TO START THIS WEEKEND, INCLUDING AN IMPACTFUL SYSTEM
MONDAY AND TUESDAY ALONG WITH A POTENTIAL SECOND STRONG STORM FOR
THE DAYS AFTER CHRISTMAS. SEE THE PREVIOUS DISCUSSION FOR MORE
INFORMATION.
DIALH
SHORT TERM
(TODAY AND TONIGHT)
ISSUED AT 351 AM PST THU DEC 19 2024
DENSE FOG HAS BEEN SLOWER TO DEVELOP AND SPREAD ACROSS OUR AREA
TONIGHT, WITH CIRRUS CONTINUING TO STREAM ACROSS THE SOUTH BAY
SLOWING RADIATIVE COOLING AS OF 3AM. DENSE FOG HAS DEVELOPED ACROSS
SOME OF THE CLOUD FREE AREAS OVER THE NORTH BAY AND EAST BAY AND
WILL EVENTUALLY FILL ACROSS THE SOUTH BAY AS THE HIGH CLOUDS SHIFT
EAST. A DENSE FOG ADVISORY REMAINS IN EFFECT THROUGH NOON PST TODAY.
HIRES GUIDANCE SUGGEST MOST OF THE FOG DISSIPATING OR MIXING OUT BY
NOON TODAY, WITH A CHANCE OF LINGERING FOG OR REDEVELOPMENT OVER
PORTIONS OF MARIN CO THROUGH THE AFTERNOON. TEMPERATURES THIS
AFTERNOON ACROSS THE NORTH BAY WILL BE VERY SIMILAR TO YESTERDAY
WITH HIGHS IN THE LOW/MID 60S, COOLER ALONG THE COAST AND BAY AREA
WHERE GRADUALLY INCREASING CLOUDS WILL HELP TO KEEP TEMPERATURES
AROUND NORMAL. INTERIOR LOCATIONS ACROSS THE SOUTH BAY AND THE
REMAINDER OF THE CENTRAL COAST WILL WARM NICELY INTO THE LOW 70S.
AREAS OF DENSE FOG ARE POSSIBLE AGAIN IN THE NORTH AND SOUTH BAY
VALLEYS LATE TONIGHT INTO EARLY FRIDAY MORNING. BY LATE TOMORROW
MORNING, THE WELL ADVERTISED PATTERN CHANGE WILL BEGIN TO TAKE SHAPE
AS SOUTHERLY OFFSHORE SURFACE FLOW OUT AHEAD OF THE STRENGTHENING
SYSTEM INCREASES TO 15-20MPH THROUGH THE REMAINDER OF THE DAY INTO
SATURDAY.
LONG TERM
(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 351 AM PST THU DEC 19 2024
THE FIRST OF SEVERAL IMPACTFUL ROUNDS OF RAIN AND WIND TAKES AIM
ACROSS OUR AREA LATE FRIDAY NIGHT INTO EARLY SATURDAY. THE SYSTEM IS
TRENDING MORE PROGRESSIVE AND HAS SHIFTED SLIGHTLY NORTH, WHICH HAS
RESULTED IN A SLIGHT DOWNWARD TREND IN EXPECTED RAINFALL AMOUNTS
THROUGH SATURDAY NIGHT OVER THE NORTH BAY. SCATTERED LIGHT RAIN WILL
PERSIST THROUGH THE NIGHT INTO EARLY SUNDAY AS A SERIES OF MIDLEVEL
SHORTWAVES EJECT OUT AHEAD OF A STRENGTHENING BAROCLINIC ZONE AND
TIGHTENING THETAE GRADIENT, THAT PUSHES ONSHORE SUNDAY NIGHT.
ALTHOUGH LIGHT RAIN CHANCES REMAIN IN THE FORECAST DURING THE DAY
ON MONDAY, THE LEADING EDGE OF A STRONG AR BEGINS TO IMPACT OUR
AREA MONDAY EVENING THROUGH TUESDAY, WITH STRONG WINDS UP TO
30-40MPH AT TIMES THROUGHOUT THE EVENT AND 2-4" OF RAINFALL ACROSS
THE NORTH BAY. PROGRESSIVE UPPER RIDGING ACROSS OUR AREA ON
CHRISTMAS DAY PROVIDES A SHORT BUFFER BEFORE THE NEXT SYSTEM
ARRIVES AFTER MIDNIGHT INTO THE EARLY HOURS OF THURSDAY.
AVIATION
(18Z TAFS)
ISSUED AT 1027 AM PST THU DEC 19 2024
SURFACE OBSERVATIONS AND SATELLITE IMAGERY SHOW LESS TO MUCH LESS
AREAL COVERAGE OF FOG AND LOW CLOUDS /IFR/ ACROSS THE BAY AREA
COMPARED TO THIS TIME WEDNESDAY. THE WMC-SFO 6.8 MB, SAC-SFO 2.2
MB PRESSURE GRADIENTS AND OFFSHORE WINDS ARE GENERALLY MORE ROBUST
THIS MORNING. CLOUD RIPPLING IS SEEN THE VISIBLE IMAGERY ACROSS
THE DELTA AND NORTH BAY, A SIGNATURE OF INCREASED WINDS AT CLOUD
LEVEL. THOSE ARE GOOD SIGNS OF MIXING WINDS EVEN THOUGH THE 12Z
OAKLAND UPPER AIR SOUNDING DID SHOW A SIMILARLY STRONG TEMPERATURE
INVERSION (CAP) THIS MORNING THAT COULD HAVE LEAD TO A SIMILARLY
FOGGY MORNING TODAY.
IFR CONDITIONS PERSISTING THROUGH LATE MORNING TO THE AFTERNOON
ACROSS THE LOWER ELEVATIONS OF THE NORTH BAY AND THE EAST BAY DUE
TO THE ADVECTION OF LOW CLOUDS AND FOG /IFR/ FROM THE CENTRAL
VALLEY/DELTA. ELSEWHERE ACROSS THE FORECAST AREA IT'S A NEAR HIGH
CONFIDENCE VFR FORECAST. FOR TONIGHT AND FRIDAY MORNING HREF DOES
SHOW LIFR-IFR CONTINUING IN THE DELTA WITH EASTERLY WINDS AND IFR
CONDITIONS MOVING LOCALLY INTO THE BAY AREA, ALONG WITH IFR
DEVELOPING OVER THE NORTH BAY VALLEYS AND INCREASING PROBABILITY
OF IFR-MVFR CEILINGS APPROACHING THE COAST FROM THE SOUTHWEST.
VICINITY OF SFO...VFR WITH AN EAST TO NORTHEAST WIND CONTINUING
TODAY AND THIS EVENING. FOR THE OVERNIGHT AND FRIDAY MORNING IT'S
A LOW TO MODERATE CONFIDENCE MVFR FORECAST WITH SURFACE VISIBILITY
LOWERING IN MIST.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...NEAR HIGH CONFIDENCE VFR TODAY AND THIS
EVENING. HOWEVER, BY FRIDAY MORNING HREF DOES SHOW AN INCREASING
PROBABILITY OF IFR 13Z-17Z. MAINLY EAST TO SOUTHEASTERLY WINDS
TODAY, TONIGHT AND FRIDAY MORNING.
MARINE
(TODAY THROUGH TUESDAY)
ISSUED AT 929 AM PST THU DEC 19 2024
CONTINUED MODERATE TO LONG PERIOD NORTHWESTERLY SWELL WILL CAUSE
AN INCREASE IN SHOALING ON HARBOR ENTRANCES AND ELEVATED SNEAKER
WAVE RISK ALONG THE COASTLINE. LIGHT TO MODERATE RAIN ARRIVES
ALONG WITH STRONG WINDS AND ELEVATED WAVE HEIGHTS BETWEEN 15 TO
19 FEET LATE FRIDAY THROUGH THE WEEKEND. THE STORM DOOR WILL THEN
REMAIN OPEN WITH ANOTHER, STRONGER, SYSTEM EXPECTED MONDAY INTO
TUESDAY AND A THIRD SYSTEM POSSIBLE LATE WEEK. WAVE HEIGHTS WILL
REMAIN ELEVATED THROUGH LATE NEXT WEEK WITH ANOTHER ROUND OF 15
TO 20 FEET WAVES EXPECTED MONDAY THROUGH WEDNESDAY. PERSISTENT
DANGEROUS CONDITIONS FOR SMALL CRAFTS ARE EXPECTED FRIDAY INTO
NEXT WEEK.
BEACHES
ISSUED AT 946 AM PST THU DEC 19 2024
A BEACH HAZARDS STATEMENT IS IN EFFECT TO 6 PM TODAY FROM SONOMA
COUNTY TO MONTEREY COUNTY. MODERATE TO LONG PERIOD NORTHWESTERLY
SWELL WILL RESULT IN ELEVATED SNEAKER WAVES WITH SNEAKER WAVES
LIKELY TO BREAK BETWEEN 10 AND 13 FEET. THE COMBINATION OF
ELEVATED SNEAKER WAVE THREAT AND RIP CURRENTS BOTH POSE A RISK TO
BEACHGOERS WHO ARE CAUGHT UNAWARE. VISITORS TO THE COAST ARE
ADVISED TO TAKE EXTRA CARE AND NEVER TURN THEIR BACKS TO THE OCEAN
AS SNEAKER WAVES MAY SWEEP UNAWARE BEACHGOERS INTO THE OCEAN.
A SECOND PERIOD OF DANGEROUS, ELEVATED SURF NEAR 15 FEET WILL OCCUR
SATURDAY MORNING TO SUNDAY AFTERNOON AS ANOTHER SYSTEM APPROACHES THE
WEST COAST.
THEN, A VERY LARGE AND POWERFUL, LONG PERIOD WEST SWELL TRAIN WILL
LIKELY ARRIVE ALONG OUR ENTIRE COASTLINE MONDAY INTO TUESDAY NEXT
WEEK. CURRENT GLOBAL WAVE MODELS ARE FORECASTING SWELL HEIGHTS TO
20+ FEET WITH VERY ENERGETIC SWELL PERIODS OF 20+ SECONDS, THIS WILL
LEAD TO MUCH HIGHER BREAKERS INCLUDING LOCALIZED COASTAL FLOODING
IMPACTS. STAY TUNED FOR FURTHER UPDATES.
MTR WATCHES/WARNINGS/ADVISORIES
CA...BEACH HAZARDS STATEMENT UNTIL 6 PM PST THIS EVENING FOR CAZ006-
505-509-529-530.
PZ...SMALL CRAFT ADVISORY FROM 3 AM TO 3 PM PST FRIDAY FOR PT ARENA
TO PT REYES 10-60 NM.
SHORT TERM...JM
LONG TERM....JM
AVIATION...CANEPA
MARINE...CANEPA
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page