096
FXUS66 KMTR 190515
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
915 PM PST MON NOV 18 2024
..NEW SYNOPSIS, UPDATE
SYNOPSIS
ISSUED AT 914 PM PST MON NOV 18 2024
COLD TEMPERATURES LINGER FOR ONE MORE NIGHT WITH FREEZE WARNINGS AND
FROST ADVISORIES IN EFFECT FROM MIDNIGHT TONIGHT THROUGH 8 AM
TOMORROW MORNING ACROSS THE INTERIOR NORTH BAY AND CENTRAL COAST.
STRONG ATMOSPHERIC RIVER BEGINS IMPACTING THE NORTH BAY WEDNESDAY,
WITH RAINFALL EXTENDING INTO THE WEEKEND. MORE WIDESPREAD RAINFALL
FRIDAY INTO THE WEEKEND. FLOODING IS POSSIBLE IN THE NORTH BAY AND
NORTHERN PARTS OF THE BAY AREA BY THE LATE WEEK.
UPDATE
ISSUED AT 914 PM PST MON NOV 18 2024
NO CHANGES TO THE FORECAST THIS EVENING AS WE DEAL WITH ONE MORE
NIGHT OF COLD TEMPERATURES BEFORE OUR FIRST IMPACTFUL ATMOSPHERIC
RIVER EVENT OF THE SEASON SETS IN ACROSS OUR REGION FOR THE SECOND
HALF OF THE WEEK INTO THE WEEKEND. THE NORTH BAY WILL SEE RAIN
CHANCES BEGIN TO INCREASE TUESDAY EVENING, WITH THE FULL FORCE OF
THE AR BEGINNING TO BE FELT BY EARLY WEDNESDAY MORNING. A FLOOD
WATCH HAS BEEN ISSUED BEGINNING AT 4 AM ON WEDNESDAY THROUGH 5 AM
FRIDAY MORNING. PORTIONS OF THE NORTH BAY WILL SEE ROUGHLY 6-8" OF
RAINFALL WITH SOME LOCALLY ENHANCED UPSLOPE LOCATIONS GETTING UP TO
10" THROUGH 5 AM FRIDAY MORNING. THERE WILL BE A SECOND ROUND OF
HEAVY RAINFALL LATER IN THE DAY ON FRIDAY THAT WILL BEGIN TO PUSH
FARTHER SOUTH AND EAST INTO OUR INTERIOR LOCATIONS. THE MORE
WIDESPREAD RAINFALL WON'T BE AS INTENSE AS THE FIRST WAVE OVER THE
NORTH BAY THAT ENDS EARLY FRIDAY MORNING. A THIRD ROUND OF RAINFALL
SUNDAY INTO MONDAY WILL ALSO BE LIGHTER, BUT WIDESPREAD ACROSS OUR
FORECAST AREA.
SHORT TERM
(THIS EVENING THROUGH TUESDAY)
ISSUED AT 224 PM PST MON NOV 18 2024
CLEAR SKIES WILL PREVAIL THROUGH THE DAY WITH BREEZY NORTHWEST
WINDS. TEMPERATURES REMAIN CHILLY WITH HIGH TEMPERATURES RANGING
FROM THE MID 50S TO THE LOW 60S IN THE LOWER ELEVATIONS, DOWN TO THE
UPPER 40S TO THE MID 50S IN THE HIGHER ELEVATIONS. A GOOD DAY TO
CLEAR OUT GUTTERS AND STORM DRAINS!
TONIGHT INTO TUESDAY MORNING, LOW TEMPERATURES WILL DROP TO THE MID
20S TO THE LOW 30S ACROSS THE INTERIOR CENTRAL COAST, AND THE 30S IN
THE INTERIOR NORTH BAY, WITH FREEZE WARNINGS IN EFFECT FOR BOTH
REGIONS. A FROST ADVISORY IS IN EFFECT FOR THE INTERIOR EAST AND
SOUTH BAYS AND SANTA CRUZ COASTAL REGIONS, WHERE LOWS DROP INTO THE
MID 30S. THESE TEMPERATURES CAN BE HAZARDOUS FOR VULNERABLE
POPULATIONS, INCLUDING CHILDREN, THE ELDERLY, UNHOUSED PEOPLE,
OUTDOOR PETS, AND LIVESTOCK. TUESDAY SHOULD SEE INCREASING CLOUD
COVER AND A SHIFT TO A SOUTH WIND, WHILE OUT IN THE NORTHEASTERN
PACIFIC, A RAPIDLY STRENGTHENING LOW PRESSURE SYSTEM WILL GATHER
SUBTROPICAL MOISTURE AND BEGIN DIRECTING IT TOWARDS THE WEST COAST.
FORESHADOWING, PERHAPS...
LONG TERM
(TUESDAY NIGHT THROUGH NEXT SUNDAY)
ISSUED AT 224 PM PST MON NOV 18 2024
KEY MESSAGES:
-STRONG ATMOSPHERIC RIVER EXPECTED TO STALL OVER THE NORTH BAY
WEDNESDAY. (SEE "METEOROLOGY AND TIMING" BELOW)
-FLOOD WATCH IS OUT FOR THE NORTH BAY WED-THU
-4-10" OF RAINFALL IN THE NORTH BAY WED-SUN
-LOCALLY UP TO 12" IN THE SONOMA COASTAL RANGES
-RAIN MOVING SOUTH ON FRIDAY, MUCH LESS RAIN (SEE "IMPACTS" BELOW)
BUCKLE UP EVERYONE... A STRONG ATMOSPHERIC RIVER WILL DEVELOP OVER
THE PACIFIC OCEAN AND STALL OUT OVER NORTHERN CALIFORNIA, INCLUDING
THE NORTH BAY, BEGINNING ON WEDNESDAY. A RAPIDLY DEVELOPING LOW
PRESSURE SYSTEM, TO THE TUNE OF AROUND A 60 MB DEEPENING IN 24 HOURS
VIA THE MODEL GUIDANCE, IN THE EAST PACIFIC WILL PULL SUBTROPICAL
MOISTURE INTO NORTHERN CALIFORNIA, WHERE IT WILL SIT OVER THE COAST
FROM EUREKA TO BODEGA BAY INTO THURSDAY AND EARLY FRIDAY. AS AN
ASIDE, THE CRITERIA FOR "BOMB CYCLOGENESIS" AROUND THE STORM'S
LATITUDE OF 42 DEGREES NORTH IS 18 MB IN 24 HOURS. IF THE MODEL
GUIDANCE FROM EARLIER PANS OUT, WE WILL EASILY DOUBLE, AND POSSIBLY
TRIPLE, THAT RATE OF DEEPENING WITH THIS LOW. IT'S AN INTERESTING
FACT, BUT IT DOESN'T HELP US COMMUNICATE THE MOST IMPORTANT PART OF
THE FORECAST: THE IMPACTS OF THE UPCOMING EVENT, ESPECIALLY AS IT
SHAPES UP TO BE OUR FIRST BIG RAINMAKER OF THE WINTER SEASON.
METEOROLOGY AND TIMING:
RAIN SHOULD START TO FALL IN THE NORTH BAY EARLY WEDNESDAY MORNING,
SLOWLY INTENSIFYING AND SPREADING SOUTH THROUGH THE DAY. INTENSE
SOUTHWEST FLOW (ABOVE 50 KNOTS AT THE 925 MB LEVEL) WILL STALL OVER
THE COAST FROM EUREKA DOWN TO THE GOLDEN GATE. AS WITH THE PREVIOUS
FORECAST, I'VE BUMPED THE WIND GUSTS ON WEDNESDAY A LITTLE HIGHER,
WITH THE END RESULT BEING GUSTS FROM 40-50 MPH ACROSS THE NORTH BAY
COAST, AND HIGHER ELEVATIONS AS FAR SOUTH AS THE SAN MATEO PENINSULA
AND THE EAST BAY HILLS.
AS WE GO INTO THURSDAY, THE INITIAL SURFACE LOW MOVES NORTHWARDS,
PARALLELING THE COAST OF THE PACIFIC NORTHWEST AND BRITISH
COLUMBIA, PULLING THE MOISTURE PLUME A LITTLE NORTH AS WELL, WHILE
ANOTHER SURFACE LOW DEVELOPS TO ITS SOUTHWEST. THAT CYCLONE ALSO HAS
THE CHANCE TO RAPIDLY DEVELOP AS IT COMES INTO THURSDAY EVENING AND
FRIDAY. MEANWHILE, THE INTENSE UPPER LEVEL LOW THAT HAS BEEN
SUPPORTING THESE TWO SYSTEMS WILL BE PUSHED TO THE EAST BY A STRONG
DOWNSTREAM JET, DISLODGING THE SYSTEM FROM ITS STALL, WITH THE
ASSOCIATED COLD FRONT DRAGGING ONTO LAND AND MOVING INLAND WITH IT.
THIS WILL BRING THE AXIS OF RAINFALL SOUTHWARD THROUGH FRIDAY INTO
THE UPCOMING WEEKEND.
MODEL GUIDANCE TRENDS HAVE MOVED THE INTENSE UPPER LEVEL JET A
LITTLE MORE TO THE SOUTH, INCREASING THE IMPACTS TO THE NORTHERN
PART OF THE SF BAY AREA. SPEAKING OF WHICH...
IMPACTS:
IMPACTS ON WEDNESDAY AND THURSDAY WILL CONCENTRATE ON THE NORTH BAY
WITH RAINFALL TOTALS RANGING FROM 3-7" IN THE VALLEYS TO 6-10"
ACROSS THE HIGHER ELEVATIONS. BASED ON THE INTENSE RAINFALL EXPECTED
WITH THIS SYSTEM, A FLOOD WATCH HAS BEEN ISSUED FOR THE NORTH BAY
EXTENDING FROM WEDNESDAY INTO LATE THURSDAY NIGHT, WITH THE MAIN
IMPACTS BEING FLOODING IN URBAN AREAS AND SMALL STREAMS. AS STATED
EARLIER, NOW IS A GOOD TIME TO CLEAR OUT GUTTERS AND STORM DRAINS,
LEST THE RESULTANT RAINFALL FIND ITSELF UNABLE TO DRAIN OFF AND POND
ONTO ROADS AND DRIP INTO BUILDINGS. THE GOOD NEWS IS THAT, AT LEAST
IN THE BEGINNING OF THE EVENT, THE SOILS ARE DRY AND WILL ABSORB THE
RAINFALL. THE BAD NEWS IS THAT THE INTENSE RAINFALL TOTALS WILL
QUICKLY SATURATE THEM AND WILL CONTRIBUTE TO FLOODING CONCERNS
HEADING INTO THE FRIDAY AND WEEKEND. EXPECT FURTHER FLOODING
PRODUCTS AS THE SYSTEM EVOLVES.
ELSEWHERE, THE INITIAL IMPACTS DIMINISH QUITE QUICKLY THE FURTHER
SOUTH YOU GO. RAINFALL TOTALS FROM WEDNESDAY AND THURSDAY RANGE FROM
1-2" IN THE NORTHERN EAST BAY AND THE NORTHERN AND WESTERN SAN MATEO
PENINSULA, INCLUDING THE CITY OF SAN FRANCISCO, 0.5-1" IN THE SANTA
CRUZ COASTAL AREAS AND THE SOUTHERN EAST BAY, 0.25"-0.5" IN THE
SANTA CLARA VALLEY, 0.1-0.25" IN THE MONTEREY BAY REGION, AND
VIRTUALLY NOTHING IN SOUTHERN MONTEREY AND SAN BENITO COUNTIES.
THE SOUTHERN PUSH OF RAIN FRIDAY INTO THE WEEKEND WILL BRING MORE
RAINFALL TO THE AREAS TO THE SOUTH OF THE GOLDEN GATE. ACROSS THE
SOUTH BAY, ADJACENT AREAS OF THE EAST BAY AND THE SAN MATEO
PENINSULA, AND THE CENTRAL COAST, THE PUSH FROM FRIDAY INTO THE
WEEKEND WILL BRING MORE RAIN THAN THE INITIAL SYSTEM ON WEDNESDAY
AND THURSDAY. FOR FRIDAY AND SATURDAY, THE CURRENT FORECAST CALLS
FOR 0.5-1.5" OF RAIN ACROSS THE BAY AREA AND MONTEREY BAY REGIONS,
WITH AROUND 2-4" OF RAIN IN THE SANTA CRUZ MOUNTAINS AND THE SANTA
LUCIAS. ALTHOUGH RAINFALL TOTALS IN THE NORTH BAY VALLEYS IN THE
SAME PERIOD ONLY REACH 1.5-3", AS EARLIER MENTIONED, THE INTENSE
RAINFALL ON THE PREVIOUS TWO DAYS COULD LEAD TO MORE WIDESPREAD
FLOODING IMPACTS, AS SOILS HAVE SATURATED AND CREEKS AND STREAMS ARE
FILLED COMPARED TO WHAT THEY ARE NOW BEFORE THE RAINFALL.
BE SURE TO PAY CLOSE ATTENTION AND STAY UP TO DATE WITH THE WEATHER
FORECAST OVER THE NEXT FEW DAYS FOR THE LATEST UPDATES AND MOST
ACCURATE INFORMATION.
AVIATION
(00Z TAFS)
ISSUED AT 402 PM PST MON NOV 18 2024
VFR CONDITIONS CONTINUE THROUGH THE TAF PERIOD. GUSTY NORTHWEST
WINDS HAVE RETURNED ACROSS THE BAY AREA AND CENTRAL COAST WITH GUSTS
UP TO 27 KNOTS EXPECTED. WINDS ARE EXPECTED TO EASE OVERNIGHT AND
BECOME MORE NORTHERLY TO SLIGHTLY NORTHEASTERLY. HIGH CLOUDS ARE
EXPECTED TO PERSIST THROUGH THE PERIOD AND GRADUALLY START TO LOWER
AHEAD OF RAIN SHOWERS LATE TUESDAY. WHILE SHOWERS BECOME MORE LIKELY
AFTER THE END OF THIS TAF PERIOD, WINDS WILL SHIFT SOUTHERLY AND
GUSTS WILL START TO INCREASE AROUND 00Z WEDNESDAY.
VICINITY OF SFO...VFR THROUGH THE TAF PERIOD. GUSTY NW WINDS
CONTINUE THROUGH THE EVENING WITH A 30 TO 40% CHANCE OF WINDS
GUSTING ABOVE 30 KNOTS. WINDS ARE EXPECTED TO WEAKEN OVERNIGHT BUT
WILL STRENGTHEN AGAIN BY TUESDAY AFTERNOON/EVENING.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...VFR THROUGH THE TAF PERIOD. HIGH CLOUDS
LINGER WITH LOWER CIGS EXPECTED TO DEVELOP AFTER THE END OF THIS TAF
PERIOD AS OUR NEXT SYSTEM APPROACHES. GUSTY NW WINDS CONTINUE
THROUGH THE EVENING BEFORE WEAKENING OVERNIGHT. WINDS WILL START TO
PICK UP TUESDAY AFTERNOON BUT STRONGER WINDS ARE EXPECTED TO DEVELOP
MARINE
(TONIGHT THROUGH NEXT SUNDAY)
ISSUED AT 402 PM PST MON NOV 18 2024
HAZARDOUS MARINE PERIOD AHEAD. NORTHWESTERLY BREEZES WILL
DIMINISH AND SEAS WILL ABATE THROUGH MONDAY. BY TUESDAY, STRONG
SOUTHERLY BREEZES WITH GALE-FORCE GUSTS WILL DEVELOP AHEAD OF THE
BOMB CYCLONE WITH WAVES BUILDING TO BECOME VERY ROUGH AGAIN IN
ITS WAKE. EXPECT HEAVY RAIN AND THUNDERSTORMS AS WELL.
MTR WATCHES/WARNINGS/ADVISORIES
CA...FLOOD WATCH FROM LATE TUESDAY NIGHT THROUGH LATE THURSDAY NIGHT
FOR CAZ502>506.
FREEZE WARNING UNTIL 8 AM PST TUESDAY FOR CAZ504-506-516>518-528.
FROST ADVISORY UNTIL 8 AM PST TUESDAY FOR CAZ510-513>515-529.
PZ...SMALL CRAFT ADVISORY FROM 9 PM TUESDAY TO 3 AM PST WEDNESDAY FOR
SF BAY N OF BAY BRIDGE.
GALE WARNING FROM 3 AM TO 3 PM PST WEDNESDAY FOR PT REYES TO
PIGEON PT 0-10 NM-SF BAY N OF BAY BRIDGE.
SMALL CRAFT ADVISORY UNTIL 9 PM PST TUESDAY FOR PT ARENA TO PT
REYES 0-10 NM.
GALE WARNING FROM 9 PM TUESDAY TO 3 PM PST WEDNESDAY FOR PT
ARENA TO PT REYES 0-10 NM.
SMALL CRAFT ADVISORY FROM 3 PM TUESDAY TO 3 AM PST WEDNESDAY FOR
PT REYES TO PIGEON PT 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 3 AM PST TUESDAY FOR PIGEON PT TO PT
PINOS 0-10 NM-PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM.
SMALL CRAFT ADVISORY FROM 9 PM TUESDAY TO 9 AM PST WEDNESDAY FOR
PIGEON PT TO PT PINOS 0-10 NM.
GALE WARNING FROM 9 AM TO 3 PM PST WEDNESDAY FOR PIGEON PT TO PT
PINOS 0-10 NM-PIGEON PT TO PT PINOS 10-60 NM.
SMALL CRAFT ADVISORY FROM 9 PM TUESDAY TO 3 PM PST WEDNESDAY FOR
PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 3 PM PST TUESDAY FOR PT ARENA TO PT
REYES 10-60 NM.
GALE WARNING FROM 3 PM TUESDAY TO 9 AM PST WEDNESDAY FOR PT
ARENA TO PT REYES 10-60 NM.
SMALL CRAFT ADVISORY UNTIL 9 AM PST WEDNESDAY FOR PIGEON PT TO
PT PINOS 10-60 NM.
SHORT TERM...DIALH
LONG TERM....DIALH
AVIATION...KENNEDY
MARINE...SARMENT
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