141
FXUS66 KMTR 200556
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
956 PM PST TUE NOV 19 2024
..NEW AVIATION
SYNOPSIS
ISSUED AT 110 PM PST TUE NOV 19 2024
A STRONG ATMOSPHERIC RIVER WILL BRING HEAVY RAIN AND STRONG WINDS TO
THE BAY AREA BEGINNING TONIGHT, WITH IMPACTS LASTING THROUGH THE
WEEKEND. THE WORST IMPACTS WILL BE FELT IN THE NORTH BAY, WHERE
MORE THAN A MONTH'S WORTH OF RAIN WILL FALL OVER THE NEXT 3-4
DAYS.
UPDATE
ISSUED AT 934 PM PST TUE NOV 19 2024
AN INTENSE, RAPIDLY DEVELOPED MID-LATITUDE LOW PRESSURE SYSTEM
BOTTOMED OUT NEAR 945 MB SURFACE PRESSURE PER OPC/WPC 00Z (4 PM
PST) ANALYSIS AND 500 MB HEIGHTS ARE NEAR 501 DECAMETERS. THE
CENTER OF THE LOW IS CURRENTLY 350 MILES WEST OF LA PUSH IN
NORTHWESTERN WASHINGTON. THE LOW IS CONNECTED TO A LONG PLUME OF
DEEP, RICH WATER VAPOR EXTENDING SOUTH ACROSS NORTHERNMOST
CALIFORNIA AND OUT TO THE SOUTHWEST AND WEST ACROSS THE PACIFIC TO
THE VICINITY OF HAWAII.
THE LARGER SCALE SOUTHERLY PRESSURE GRADIENT SFO-ACV AT 12.8 MB
CONTINUES TO STEEPEN, WHILE ONLY SEEING MORE MODEST INCREASES SO
FAR IN GRADIENTS SMX-SFO 2.2 MB, STS-UKI 0.7 MB AND SNS-SJC 1.2
MB. OVER THE NORTHERN COASTAL WATERS AND ACROSS THE BAY AREA AND
NORTH CENTRAL COAST HILLTOPS AND MOUNTAINTOPS WINDS ARE PICKING
UP FROM THE SOUTH AND GUSTY. LOWER ELEVATIONS WINDS ARE MAINLY
DECOUPLED AND MAINLY LIGHT SINCE THE VERTICAL TEMPERATURE PROFILE,
NEAR SURFACE TO SURFACE DEWPOINT TEMPS ARE LOW (DRY) SUPPORTING
EVAPORATIVE COOLING ALONG THE LEADING EDGE OF LIGHT RAIN AND IN
GENERAL SUPPORTING NOCTURNAL AIR MASS STABILITY. THE WARM FRONT
TEMPERATURE INVERSION WAS SEEN ON THE 00Z OAKLAND UPPER AIR SOUNDING
BEGINNING NEAR THE 600 MB LEVEL (~ 14000 FEET). OVERNIGHT INTO
WEDNESDAY MORNING VALLEY WINDS AND WINDS ALOFT WILL GRADUALLY
RECOUPLE WITH THE SURFACE WINDS, BECOMING GUSTY. AS ADVERTISED
STEADY RAIN IS FORECAST TO ARRIVE OVERNIGHT AND WEDNESDAY MORNING
ACROSS SONOMA, NAPA, MARIN COUNTIES FIRST THEN GRADUALLY SPREADING
SOUTHEASTWARD ACROSS THE REST OF THE BAY AREA WEDNESDAY.
SHORT TERM
(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 110 PM PST TUE NOV 19 2024
KEY MESSAGES:
-STRONG ATMOSPHERIC RIVER EXPECTED TO ARRIVE IN THE NORTH BAY
TONIGHT.
-FLOOD WATCH IS OUT FOR THE NORTH BAY WED-SAT
-WIND ADVISORY IN THE NORTH BAY AND SAN FRANCISCO BAYSHORE AND
PACIFIC COAST TONIGHT-EARLY THU FOR GUSTS UP TO 45-50 MPH
-4-10" OF RAINFALL IN THE NORTH BAY WED-SUN
-LOCALLY UP TO 15" IN THE SONOMA COASTAL RANGES
-RAIN MOVING SOUTH ON FRIDAY, 1-3" OF RAIN ACROSS THE REGION THROUGH
THE WEEKEND
SKIES ARE CLOUDING UP ACROSS THE BAY AREA AND SOUTHERLY WINDS ARE
STARTING TO BUILD, AS AN INTENSE, RAPIDLY DEVELOPING CYCLONE OFF THE
WEST COAST BRINGS A PLUME OF SUBTROPICAL MOISTURE TO THE REGION.
RADAR IS ALREADY PICKING UP ON ECHOES RIGHT ON THE NORTHERN SONOMA
COAST AND OFFSHORE, BUT REPORTS OF MEASURABLE PRECIPITATION ARE
MAINLY LIMITED TO THE NORTH COAST CLOSER TO EUREKA. THE FORECAST FOR
TODAY CALLS FOR BUILDING SOUTH WINDS THROUGH THE DAY, LEADING UP TO
A WIND ADVISORY COMING INTO EFFECT TONIGHT ACROSS THE NORTH BAY, THE
CITY OF SAN FRANCISCO, THE PACIFIC COAST OF SAN MATEO PENINSULA, AND
THE SAN FRANCISCO BAYSHORE, DUE TO GUSTS UP TO 45-50 MILES PER HOUR
ALONG THE COAST, AT THE RIDGELINES, AND THROUGH THE GAPS AND
PASSES. RAIN WILL BEGIN IN THE NORTH BAY LATER TONIGHT AND WILL
START TO SPREAD SOUTHWARD AND INTENSIFY BY WEDNESDAY, WITH A FLOOD
WATCH COMING INTO EFFECT WEDNESDAY MORNING FOR THE NORTH BAY FOR
FLOODING OF URBAN AREAS AND SMALL CREEKS AND STREAMS DUE TO THE
SHEER VOLUME OF RAINFALL EXPECTED ACROSS THE REGION. BY THE END OF
WEDNESDAY, THE NORTH BAY VALLEYS ARE EXPECTED TO RECEIVE 1-4" OF
RAIN, WITH TOTALS OF 4-6" AND LOCALLY TO 8" IN THE SONOMA COASTAL
RANGES AND THE MAYACAMAS. RAIN TOTALS WILL DECREASE DRAMATICALLY
THE FURTHER SOUTH YOU GO, WITH THE AREA AROUND SAN FRANCISCO AND
OAKLAND EXPECTED TO RECEIVE AROUND 0.5-1" OF RAIN, AND IN SAN JOSE
SOUTHWARD TO THE CENTRAL COAST, YOU WOULD BE FORGIVEN FOR
THINKING THAT NOTHING TOO SIGNIFICANT WAS HAPPENING.
METEOROLOGICAL NERD NOTE: HOW RAPIDLY IS THE CYCLONE OFFSHORE
DEEPENING? PRETTY QUICKLY, IT TURNS OUT. AS OF 12Z (4 AM) THIS
MORNING, OUR COLLEAGUES AT THE OCEAN PREDICTION CENTER ANALYZED THE
LOW AT 981 MILLIBARS. SIX HOURS EARLIER, THEIR ANALYSIS WAS 1000
MILLIBARS. GOING BACK TO THIS MORNING'S FORECAST DISCUSSION, AT THE
LATITUDE OF THE STORM SYSTEM, "BOMB CYCLOGENESIS" OCCUR WITH A
DEEPENING OF AT LEAST 19 MB IN 24 HOURS. THE OPC ANALYSIS HAD A DROP
OF 19 MB WITHIN 6 HOURS. IN ADDITION, IF THE OPC FORECAST OF A
MINIMUM PRESSURE OF 943 MB LATER TODAY VERIFIES, IT WOULD CHALLENGE
THE LOWEST PRESSURE ON RECORD IN THE NORTHEASTERN PACIFIC, WITH A
BUOY OFF THE COAST OF WASHINGTON STATE REPORTING A PRESSURE OF 942.5
MB IN OCTOBER 2021.
LONG TERM
(WEDNESDAY NIGHT THROUGH NEXT MONDAY)
ISSUED AT 110 PM PST TUE NOV 19 2024
THE INTENSE RAINFALL ACROSS THE NORTH BAY CONTINUES THROUGH
THURSDAY, AS THE MOISTURE PLUME REMAINS OVER THE REGION. RAINFALL
TOTALS ON THURSDAY ARE EFFECTIVELY THE SAME AS THE FORECAST FOR
WEDNESDAY'S RAINFALL TOTALS. ONE THING THAT WILL DIMINISH ON
THURSDAY ARE THE WINDS, WHERE THE GUSTS ARE EXPECTED TO DIMINISH
THROUGH THE DAY. AS A RESULT, THE WIND ADVISORY IS EXPECTED TO
EXPIRE THURSDAY MORNING.
BY FRIDAY, THE PLUME OF MOISTURE WILL BEGIN TO MIGRATE SOUTHWARD,
GIVING THE REST OF THE BAY AREA AND CENTRAL COAST A TASTE OF THE
STRONG RAIN. THE RAINFALL TOTALS ARE NOT EXPECTED TO BE AS HIGH AS
THOSE SEEN ACROSS THE NORTH BAY, BUT STILL PRETTY SIZEABLE: THROUGH
SATURDAY MORNING, THE SANTA CRUZ AND SANTA LUCIA MOUNTAINS ARE DUE
FOR AROUND 1.5-3" OF RAIN, WHILE AROUND 1-2" OF RAIN IS EXPECTED
ACROSS THE BAY AREA VALLEYS, AND AROUND 0.3-1" IN THE CENTRAL COAST.
MEANWHILE, THE NORTH BAY CONTINUES TO SEE RAIN TO THE TOTAL OF 1.5-
4" FROM FRIDAY TO SATURDAY MORNING, AND EVEN THOUGH THE RAINFALL
TOTALS MIGHT NOT BE AS EXTREME, THE FLOODING CONCERNS WILL INCREASE
COMPARED TO THOSE SEEN IN THE FIRST TWO DAYS OF THE SYSTEM. THE
FLOOD WATCH IS NOW OUT THROUGH SATURDAY MORNING, AND DEPENDING ON
THE EVOLUTION OF THE FORECAST, MIGHT NEED TO BE EXTENDED FURTHER. AS
OF THE LATEST FORECASTS FROM THE RIVER FORECAST CENTER IN
SACRAMENTO, THERE IS A 30% PROBABILITY OF SEEING MINOR FLOODING AT
THE MARK WEST CREEK AT MIRABEL HEIGHTS OVER THE NEXT 5 DAYS, AND A
43% PROBABILITY OF MINOR FLOODING AT THE LAGUNA DE SANTA ROSA AT
COTATI DURING THE SAME PERIOD. THE LARGER RIVERS ARE NOT EXPECTED TO
FLOOD, BUT THEY WILL RISE PRETTY SIGNIFICANTLY. THE RUSSIAN RIVER AT
GUERNEVILLE, CURRENTLY MEASURED AT 5.6 FEET, RISES ABOVE 20 FEET
SOMETIME ON FRIDAY. FORTUNATELY, MINOR FLOOD STAGE THERE IS 32 FEET.
LINGERING SHOWERS AND RAIN CHANCES CONTINUE INTO THE EARLY PART OF
NEXT WEEK. CHANCES FOR THUNDERSTORMS ALSO APPEAR ON FRIDAY, WHEN THE
COLD FRONT AND THE TRIPLE POINT LOW COME ONSHORE IN NORTHERN
CALIFORNIA, A PATTERN THAT HAS HISTORICALLY LED TO STRONG
THUNDERSTORM ACTIVITY IN THE PAST.
METEOROLOGY:
THE LOW PRESSURE SYSTEM WILL NORTHWARD INTO THURSDAY,
PARALLELING THE COAST OF THE PACIFIC NORTHWEST AND BRITISH COLUMBIA,
AND BEGINS TO WEAKEN, THUS RELAXING THE PRESSURE GRADIENT FORCE
ACROSS THE STATE, CAUSING THE AFOREMENTIONED RELAXATION OF THE WIND
GUSTS.
AS THE FIRST LOW MOVES NORTHWARD, A SECOND LOW PRESSURE SYSTEM FORMS
TO ITS SOUTHWEST, MAINTAINING THE FLOW OF MOISTURE TO THE WEST
COAST. THE OPC FORECAST HAS THE LOW PRESSURE SYSTEM STRENGTHENING
FROM 1004 MB ON THURSDAY MORNING, TO 980 MB ON FRIDAY MORNING, WHICH
WOULD TECHNICALLY MEET "BOMB CYCLOGENESIS" CRITERIA, IF NOT AS
IMPRESSIVELY AS THE FIRST CYCLONE. AT THE SAME TIME, THE UPPER LEVEL
CYCLONE THAT HAS BEEN SUPPORTING BOTH OF THESE SYSTEMS WILL START TO
MOVE OFF TO THE EAST, HELPING TO "FLATTEN OUT" THE UPPER LEVEL FLOW
INTO A MORE ZONAL PATTERN.
HEADING INTO THE EARLY PART OF NEXT WEEK, UNCERTAINTY IN THE MODEL
SOLUTIONS BEGINS TO INCREASE. TAKING THE NEXT TUESDAY FOR
DEMONSTRATION, MODEL ENSEMBLE CLUSTER ANALYSIS REVEALS THAT AROUND
30% OF THE ENSEMBLE MEMBERS ARE SUGGESTING THE POTENTIAL FOR A
SECOND BIG RAINFALL EVENT. THE OTHER 70% ARE INSTEAD SHOWING A NON-
EVENT FOR OUR REGION, AND OF THOSE, A LITTLE OVER A HALF OF THEM ARE
SHOWING MORE FOCUSED RAINFALL OVER THE ALASKAN PANHANDLE AND BRITISH
COLUMBIA, WITH A SUBSTANTIAL MINORITY SHOWING THE POSSIBILITY FOR A
ROBUST MOISTURE PLUME IN THAT DIRECTION. FOR NOW, THE MESSAGING
AFTER THE UPCOMING WEEKEND REMAINS VAGUE IN DEFERENCE TO THE
SIGNIFICANT SPREAD IN THE MODEL OUTPUTS.
FINALLY, A WORD ABOUT WHY THE NORTH BAY FLOODING CONCERNS INCREASE
WITH THE RELATIVELY LIGHTER RAINFALL ON FRIDAY ONWARD: WHEN WE BEGIN
TO SEE THE RAINFALL ON WEDNESDAY, THE SOILS ARE DRIED OUT AND THE
CREEKS AND STREAMS ARE RUNNING LOW, DUE TO THE DRYNESS OF THE SUMMER
MONTHS. HOWEVER, THE INTENSE RAINFALL ACROSS THE NORTH BAY WILL HELP
QUICKLY SATURATE THE SOILS AND FILL THE CREEKS AND STREAMS. FOR
CONTEXT, THE FORECAST RAINFALL TOTAL FROM WEDNESDAY THROUGH FRIDAY
IN THE SANTA ROSA AREA RANGES AROUND 4-5 INCHES OF RAIN, WHILE THE
AVERAGE RAINFALL TOTAL FOR THE ENTIRE MONTH OF NOVEMBER IS 3.75
INCHES. IN NAPA, THE FORECAST FOR AROUND 2.5-3.5 INCHES OF RAIN
COMPARES TO A NOVEMBER RAINFALL AVERAGE OF 2.77 INCHES.
AVIATION
(06Z TAFS)
ISSUED AT 956 PM PST TUE NOV 19 2024
GUSTY SOUTHERLY WINDS ARE EXPECTED TO DEVELOP OVERNIGHT AND PERSIST
THROUGH THE END OF THE TAF PERIOD. GUSTS WILL PRIMARILY PEAK BETWEEN
30 TO 40 KNOTS BUT ENSEMBLE GUIDANCE IS STILL DISPLAYING SOME
POTENTIAL FOR GUSTS GREATER THAN 40 KNOTS TO DEVELOP DURING THE LATE
MORNING/AFTERNOON TIMEFRAME. LOCAL WRF GUIDANCE CONTINUES TO KEEP
WINDS PEAKING AROUND 40 KNOTS SO WILL CONTINUE TO LEAN MORE TOWARDS
ITS OUTPUT. LIGHT SHOWERS WILL MOVE INTO THE NORTH BAY OVERNIGHT
BEFORE MORE MODERATE SHOWERS DEVELOP BY EARLY TOMORROW MORNING.
SHOWERS WILL SPREAD SOUTHWARD WITH LIGHT RAIN EXPECTED ACROSS THE
BAY AREA BY MID MORNING. AS MORE MODERATE SHOWERS DEVELOP, DECREASES
IN CEILING HEIGHTS AND VISIBILITIES ARE EXPECTED WITH WIDESPREAD
MVFR CONDITIONS BECOMING MORE LIKELY BY TOMORROW MORNING/AFTERNOON.
VICINITY OF SFO...PUSHED BACK THE ARRIVAL OF GUSTY SOUTHERLY WINDS
TO SFO TO 09Z WITH GUSTS GREATER THAN 35 KNOTS NOW LOOKING MORE
LIKELY TO DEVELOP AFTER 14Z. GUSTS ARE EXPECTED TO PEAK AROUND 40
KNOTS DURING THE AFTERNOON/EVENING HOURS WITH SOME POTENTIAL FOR
STRONGER GUSTS TO CONTINUE OVERNIGHT WEDNESDAY INTO THURSDAY.
CEILINGS WILL CONTINUE TO LOWER THROUGH THE TAF PERIOD WITH MVFR
CONDITIONS SET TO RETURN BY EARLY TOMORROW AFTERNOON. LIGHT RAIN IS
EXPECTED TO REACH SFO BY THE EARLY AFTERNOON AND CONTINUE THROUGH
THE END OF THE TAF PERIOD.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...GUSTY SOUTHERLY WINDS ARE EXPECTED TO
DEVELOP AT SNS OVERNIGHT AND PERSIST THROUGH THE END OF THE TAF
PERIOD. LIGHT TO MODERATE SOUTHERLY WINDS CONTINUE AT MRY THROUGH
THE TAF PERIOD. SHOWER CHANCES WILL GRADUALLY INCREASE THROUGHOUT
THE LATE MORNING INTO THE AFTERNOON/EVENING WITH LIGHT RAIN POSSIBLE
AT MRY. CHANCES ARE SLIGHTLY LOWER FOR SNS BUT CANNOT RULE OUT A
STRAY SHOWER IN THE VICINITY OF THE AIRPORT.
MARINE
(TONIGHT THROUGH NEXT MONDAY)
ISSUED AT 851 PM PST TUE NOV 19 2024
A RARE HURRICANE FORCE STORM IS DEVELOPING IN THE NORTHEASTERN
PACIFIC AND MOVING TOWARDS THE COAST OF OREGON. STORM FORCE WINDS
CONTINUE OVER THE FAR NORTHERN OUTER WATERS THROUGH EARLY WEDNESDAY
MORNING WHEN THEY WILL WEAKEN SLIGHTLY AND RETURN TO HIGH END GALE
FORCE WINDS. HIGH END GALE FORCE WINDS, WITH THE POTENTIAL FOR THE
OCCASIONAL STORM FORCE GUST, WILL THEN CONTINUE ACROSS THE OUTER AND
INNER COASTAL WATERS FROM POINT ARENA TO PIGEON POINT FROM EARLY
WEDNESDAY MORNING THROUGH THE AFTERNOON. VERY ROUGH SEAS WILL
QUICKLY BUILD, AND SIGNIFICANT WAVE HEIGHTS WILL REACH 14-20 FT BY
WEDNESDAY. ALL BUT THE LARGEST, MOST SEAWORTHY CRAFT SHOULD AVOID
THE WATER THIS WEEK.
MTR WATCHES/WARNINGS/ADVISORIES
CA...WIND ADVISORY UNTIL 6 AM PST THURSDAY FOR CAZ006-502>506-508-509.
HIGH SURF ADVISORY FROM 6 AM WEDNESDAY TO 6 AM PST FRIDAY FOR
CAZ006-505-509-530.
FLOOD WATCH FROM 4 AM PST WEDNESDAY THROUGH LATE FRIDAY NIGHT
FOR CAZ502>506.
BEACH HAZARDS STATEMENT FROM 6 AM PST WEDNESDAY THROUGH LATE
THURSDAY NIGHT FOR CAZ529.
PZ...SMALL CRAFT ADVISORY UNTIL 3 AM PST WEDNESDAY FOR PT PINOS TO PT
PIEDRAS BLANCAS 0-10 NM-PT REYES TO PIGEON PT 0-10 NM-SF
BAY N OF BAY BRIDGE.
GALE WARNING FROM 3 AM TO 3 PM PST WEDNESDAY FOR SF BAY N OF BAY
BRIDGE.
SMALL CRAFT ADVISORY FROM 3 AM WEDNESDAY TO 3 AM PST THURSDAY
FOR MRY BAY.
GALE WARNING UNTIL 9 AM PST THURSDAY FOR PT ARENA TO PT REYES 0-
10 NM.
GALE WARNING FROM 3 AM WEDNESDAY TO 3 AM PST THURSDAY FOR PT
PINOS TO PT PIEDRAS BLANCAS 0-10 NM-PT REYES TO PIGEON PT 0-
10 NM.
SMALL CRAFT ADVISORY UNTIL 9 AM PST WEDNESDAY FOR PIGEON PT TO
PT PINOS 0-10 NM-PIGEON PT TO PT PINOS 10-60 NM.
GALE WARNING FROM 9 AM WEDNESDAY TO 3 AM PST THURSDAY FOR PIGEON
PT TO PT PINOS 0-10 NM-PIGEON PT TO PT PINOS 10-60 NM.
STORM WARNING UNTIL 3 AM PST WEDNESDAY FOR PT ARENA TO PT REYES
10-60 NM.
SHORT TERM...DIALH
LONG TERM....DIALH
AVIATION...KENNEDY
MARINE...KENNEDY
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