723
FXUS66 KMTR 191123
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
323 AM PST TUE NOV 19 2024
..NEW SYNOPSIS, SHORT TERM, LONG TERM, MARINE
SYNOPSIS
ISSUED AT 304 AM PST TUE NOV 19 2024
A STRONG ATMOSPHERIC RIVER WILL BRING HEAVY RAIN AND STRONG WINDS
TO THE BAY AREA STARTING TONIGHT, WITH IMPACTS EXTENDING 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.
SHORT TERM
(TODAY AND TONIGHT)
ISSUED AT 304 AM PST TUE NOV 19 2024
HIGH CLOUDS ARE STREAMING ACROSS THE CWA, LIMITING RADIATIONAL
COOLING AND KEEPING THE SURFACE TEMPERATURE A COUPLE DEGREES WARMER
THAN WE ANTICIPATED AT THIS HOUR, BUT STILL 5-10 DEGREES COOLER THAN
AVERAGE, AND FROST/FREEZE PRODUCTS ARE IN EFFECT FOR MUCH OF THE
INTERIOR THROUGH 8 AM. THAT SAID, THE NORTHERN SALINAS VALLEY IS
PROVING RESILIENT, AND REMAINS IN THE LOW TO MID 40S AT THIS
HOUR. AFTER THE SUN COMES UP, SOUTHERLY WINDS WILL GRADUALLY
INCREASE THROUGH THE DAY AS THE EXPLOSIVE CYCLOGENESIS GETS
UNDERWAY OFF THE COAST OF THE PACIFIC NORTHWEST. WINDS WILL REACH
20-30 MPH WITH GUST TO 45 MPH ACROSS THE NORTH BAY, BAY SHORE AND
PENINSULA COAST INCLUDING THE CITY OF SAN FRANCISCO. RAIN WILL
ALSO BEGIN IN THE NORTH BAY OVERNIGHT, SPREADING SOUTH WITH
INCREASING INTENSITY THROUGH THE NIGHT.
LONG TERM
(WEDNESDAY THROUGH MONDAY)
ISSUED AT 304 AM PST TUE NOV 19 2024
IMPACTS AND TIMELINE:
BY THE TIME THE SUN COMES UP WEDNESDAY (OR WHEN THE CLOUDS BECOME A
SLIGHTLY LIGHTER SHADE OF DARK GREY) THE NORTH BAY WILL BE DEALING
WITH HEAVY RAIN, WHICH WILL TAPER OFF WITH DECREASING LATITUDE AND
ONLY LIGHT RAIN IS EXPECTED SOUTH OF SAN JOSE OR SANTA CRUZ. IN THE
NORTH BAY SPECIFICALLY, THERE MAY ALSO BE SOME FLOODING OF SMALL
CREEKS AND STREAMS, AS WELL AS A FEW DOWNED BRANCHES AND TREES IN
THE STRONG OVERNIGHT WIND. IT LOOKS NASTY ALL DAY WITH STRONG WIND
AND HEAVY RAIN CONTINUING. THIS IS ESPECIALLY TRUE NORTH OF THE
GOLDEN GATE, BUT WEDNESDAY WILL BE AN IMPACTFUL DAY ACROSS MUCH OF
THE BAY AREA. THERE IS A BRIEF REPRIEVE ON THURSDAY, BUT ONLY IN
COMPARISON TO WEDNESDAY. IT WILL STILL BE RAINING FOR THE MAJORITY
OF THE DAY, AND AGAIN FOCUSED IN THE NORTH BAY. THE WINDS SHOULD
IMPROVE BELOW ADVISORY CRITERIA ON THURSDAY, BUT ONLY JUST. THE COLD
FRONT WILL FINALLY PUSH THROUGH FRIDAY WITH ANOTHER PUSH OF HEAVIER
RAIN AND STRONGER WIND AHEAD OF FRONTAL PASSAGE AND STRONGER SHOWERS
AND POTENTIAL THUNDERSTORMS DURING AND AFTER FRONTAL PASSAGE. FOR
AREAS SOUTH OF SAN FRANCISCO, THIS WILL LIKELY BRING THE HEAVIEST
RAINFALL OF THE WEEK. THE CUMULATIVE EFFECTS OF THIS RAIN WILL START
TO BE FELT ALONG THE NORTH BAY CREEKS AND STREAMS. THE CALIFORNIA
NEVADA RIVER FORECAST CENTER SHOWS A 25% CHANCE OF MARK WEST CREEK
REACHING MINOR FLOOD STAGE AND A 5% CHANCE OF REACHING MODERATE. THE
LARGER RIVERS ARE NOT EXPECTED TO APPROACH FLOODING LEVELS THIS
WEEK, BUT WILL RISE SUBSTANTIALLY FROM THEIR SEASONAL HIBERNATION.
FOR EXAMPLE, THE RUSSIAN RIVER AT GUERNEVILLE STAGE IS CURRENTLY
MEASURED AT 5.6 FT AND FORECAST TO CLIMB ABOVE 20 FEET BY
SATURDAY. FORTUNATELY THE FLOOD STAGE HERE STARTS AT 32 FEET.
SINCE THE BIG RIVERS ARE STARTING WITH A LOT OF CAPACITY, THE
FLOODING CONCERN IS FOCUSED ON THE SMALLER, FLASHIER CREEKS AND
STREAMS THROUGHOUT THE NORTH BAY, AS WELL AS PONDING ON ROADWAYS
AND LOW-LYING FLOOD PRONE URBAN AREAS. THE CONDITIONS WILL FINALLY
BEGIN TO IMPROVE GOING INTO THE WEEKEND, BUT PERSISTENT LIGHTER
RAIN LOOKS TO CONTINUE WELL INTO NEXT WEEK.
METEOROLOGY:
LET'S PUT THIS "EXPLOSIVE CYCLOGENESIS" OR "BOMB CYCLONE" IN
PERSPECTIVE. THE OCEAN PREDICTION CENTER ANALYZED THE CENTRAL
PRESSURE TO BE 1011 MB AT 19/00Z. THE 24 HOUR FORECAST DROPPED THE
PRESSURE TO 943 MB BY 20/00Z. A DROP OF 68 MB IN 24 HOURS. SO
WHAT? AT THIS STORM'S LATITUDE (43N), A CYCLONE NEEDS TO DROP 19
MB IN 24 HOURS TO CLASSIFY AS "BOMB CYCLONE". AGAIN THE OPC IS
FORECASTING A 68 MB DROP. THAT EQUATES TO 3.6 BERGERON UNITS.
EASILY PASSING THE BENCHMARK FOR A "TRIPLE BOMB". IN FACT, IF THE
FORECAST HOLDS, 943 MB IS APPROACHING THE LOWEST PRESSURE EVER
ANALYZED IN THIS PART OF THE OCEAN AND MAY PRODUCE HISTORIC WIND
SPEEDS. THE MEDFORD, OR OFFICE HAS ISSUED A VERY RARE HURRICANE
FORCE WIND WARNING FOR COASTAL WATERS FROM TUESDAY MORNING THROUGH
WEDNESDAY MORNING. IN THEIR AFD, MEDFORD NOTES THIS TYPE OF STORM
COMES AROUND ONCE A DECADE OR SO. WHILE THIS PARAGRAPH
DEMONSTRATES THE STRENGTH OF THIS CYCLONE, THE WORST IMPACTS WILL
STAY NORTH OF THE BAY AREA.
HOW MUCH RAIN ARE WE EXPECTING? THERE IS SURPRISINGLY GOOD AGREEMENT
IN THE MODEL GUIDANCE THAT THIS WILL BE A MAJOR RAIN MAKER FOR THE
NORTH BAY. THE ECMWF ENSEMBLE SHOWS A 90% CHANCE THAT SANTA ROSA
WILL SEE MORE THAN 4" OF RAIN THIS WEEK. THAT'S PRETTY UNUSUAL TO
HAVE SUCH HIGH CONFIDENCE IN GETTING AT LEAST A MONTH'S WORTH OF
RAIN OVER A FEW DAYS. THERE IS SOME SPREAD BETWEEN THE FLOOR AND
CEILING, WITH A 10% CHANCE OF SANTA ROSA GETTING OVER 10" FROM WED-
FRI. IF THE HIGH END VERIFIES, THAT WOULD APPROACH THE HIGHEST 3 DAY
TOTAL EVER RECORDED AT SANTA ROSA (9.96" FROM OCT 24-26 2021,
RECORDS GOING BACK TO 1902). THERE WILL BE A PRETTY SHARP GRADIENT
WITH LESS RAIN FURTHER SOUTH ON WEDNESDAY AND THURSDAY. AS THE
PARENT CYCLONE OCCLUDES AND WEAKENS AND THE COLD FRONT BECOMES
THE DOMINATE PLAYER, THE RAIN WILL BE MORE EVENLY DISTURBED FRI-
SAT. BY THE END OF THE WEEK NEARLY EVERYONE CAN EXPECT AT LEAST
AN INCH OR 2 IN THEIR RAIN GAUGE.
THE BEST CHANCE FOR THUNDERSTORMS IS ON FRIDAY AS THE COLD FRONT
AND NEW TRIPLE POINT LOW COME ASHORE IN NORTHERN CALIFORNIA.
HISTORY HAS TAUGHT US THAT THIS TYPE OF "LANDFALLING" OCCLUSION HAS
THE POTENTIAL TO GENERATE STRONG THUNDERSTORMS IN OUR AREA.
REGARDING THE NEW WIND ADVISORY, WE ARE CONTINUING TO BLEND 50/50
NBM WITH NBM90 TO EFFECTIVELY BUMP UP THE DETERMINISTIC WIND
SPEEDS. WHY? THE DETERMINISTIC NBM IS LAGGING BEHIND OTHER SHORT
RANGE GUIDANCE AND ALL BIAS CORRECTED MODELS STRUGGLE WITH EXTREME
EVENTS. WHILE THESE WINDS AREN'T NECESSARILY EXTREME, THIS
SYNOPTIC PATTERN IS, AND THAT IS LIKELY NOT BEING CAPTURED WELL
IN THE DETERMINISTIC NBM.
AVIATION
(06Z TAFS)
ISSUED AT 959 PM PST MON NOV 18 2024
VFR THROUGH THE TAF PERIOD. WINDS EASE AND BECOME LOCALLY VARIABLE
AT TIMES WITH MOST SITES EXPECTED TO TEMPORARILY SHIFT NORTH TO
NORTHEASTERLY OVERNIGHT. BEGINNING DURING THE EARLY MORNING HOURS,
WINDS WILL SHIFT TO A MORE SOUTHERLY DIRECTION THROUGHOUT THE BAY
AREA WITH MODERATE WINDS EXPECTED DURING THE DAY. GUSTY SOUTHERLY
FLOW WILL DEVELOP TOWARDS THE END OF THE TAF PERIOD AS THE PRESSURE
GRADIENT TIGHTENS IN RESPONSE TO OUR INCOMING LOW PRESSURE SYSTEM.
HIGH CLOUDS WILL GRADUALLY START TO LOWER LATE TUESDAY INTO
WEDNESDAY BUT CIGS ARE EXPECTED TO REMAIN VFR THROUGH THE END OF
THIS PERIOD. PRECIPITATION CHANCES INCREASE ACROSS THE NORTH BAY AND
SF BAY REGION TUESDAY EVENING AND INCREASE ELSEWHERE OVERNIGHT
TUESDAY INTO WEDNESDAY. RAIN IS INITIALLY EXPECTED TO BE FAIRLY
LIGHT ACROSS THE NORTH BAY TUESDAY EVENING. HOWEVER, RAIN IS
EXPECTED TO BECOME MORE WIDESPREAD AND HEAVIER OVERNIGHT TUESDAY
INTO WEDNESDAY WITH MORE WIDESPREAD IMPACTS FROM OUR INCOMING AR
BEGINNING TO BE FELT BEGINNING LATE TUESDAY INTO WEDNESDAY.
VICINITY OF SFO...VFR. NORTHWESTERLY FLOW WILL GRADUALLY WEAKEN AND
BECOME SOUTHERLY BY MID TOMORROW MORNING. SOUTHERLY WINDS WILL
GRADUALLY STRENGTHEN THROUGHOUT THE DAY, BECOMING MODERATE DURING
THE AFTERNOON AND GUSTY BY THE EVENING. CONFIDENCE IS INCREASING
THAT STRONG GUSTS IN EXCESS OF 30 MPH WILL DEVELOP AFTER MIDNIGHT ON
WEDNESDAY WITH GUIDANCE SHOWING A 65% CHANCE OF THIS OCCURRING.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...VFR. LIGHT, VARIABLE AT TIMES TO SOUTHERLY
WINDS WILL CONTINUE THROUGH THE TAF PERIOD WITH WINDS EXPECTED TO
TEMPORARILY BECOME NORTHWESTERLY DURING THE DAY. HIGH CLOUDS ARE
EXPECTED TO PERSIST THROUGH THE PERIOD WITH ELEVATED RAIN CHANCES
AND LOWER CIGS EXPECTED BY MID TOMORROW MORNING.
MARINE
(TONIGHT THROUGH NEXT SUNDAY)
ISSUED AT 959 PM PST MON NOV 18 2024
SEAS REMAIN ELEVATED WHILE WINDS TEMPORARILY EASE OVERNIGHT.
HAZARDOUS MARINE CONDITIONS WILL RETURN TUESDAY AS STRONG
SOUTHERLY BREEZES AND WIDESPREAD GALE-FORCE GUSTS DEVELOP AHEAD
OF AN APPROACHING BOMB CYCLONE. SEAS WILL BUILD AS THIS SYSTEM
APPROACHES WITH ROUGH SEAS RETURNING TUESDAY AND CONTINUING
THROUGH FRIDAY. WHILE WAVE HEIGHTS WILL GENERALLY PEAK BETWEEN 10
TO 16 FEET, THE NORTHERN OUTER WATERS MAY SEE WAVE HEIGHTS PEAK
CLOSER TO 20 FEET. EXPECT HEAVY RAIN BEGINNING LATE TUESDAY AND
INCREASING THUNDERSTORM CHANCES THURSDAY INTO THE WEEKEND.
MARINE
(TODAY THROUGH SUNDAY)
ISSUED AT 304 AM PST TUE NOV 19 2024
A RARE HURRICANE FORCE STORM IS DEVELOPING IN THE NE PACIFIC AND
MOVING TOWARDS THE COAST OF OREGON. WIDESPREAD GALE FORCE WINDS
WILL IMPACT THE COASTAL WATERS STARTING THIS 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 FROM 10 PM THIS EVENING TO 6 AM PST THURSDAY FOR
CAZ006-502>506-508-509.
FLOOD WATCH FROM LATE TONIGHT THROUGH LATE THURSDAY NIGHT FOR
CAZ502>506.
FREEZE WARNING UNTIL 8 AM PST THIS MORNING FOR CAZ504-506-
516>518-528.
FROST ADVISORY UNTIL 8 AM PST THIS MORNING FOR CAZ510-513>515-
529.
PZ...SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 3 AM PST
WEDNESDAY FOR 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 TO 9 PM PST WEDNESDAY FOR MRY BAY.
SMALL CRAFT ADVISORY UNTIL 9 PM PST THIS EVENING FOR PT ARENA TO
PT REYES 0-10 NM.
GALE WARNING FROM 9 PM THIS EVENING TO 9 PM PST WEDNESDAY FOR PT
ARENA TO PT REYES 0-10 NM.
SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 3 AM PST
WEDNESDAY FOR PT REYES TO PIGEON PT 0-10 NM.
GALE WARNING FROM 3 AM TO 9 PM PST WEDNESDAY FOR PT REYES TO
PIGEON PT 0-10 NM.
SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 9 AM PST
WEDNESDAY FOR PIGEON PT TO PT PINOS 0-10 NM.
GALE WARNING FROM 9 AM TO 9 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 THIS EVENING TO 9 PM PST
WEDNESDAY FOR PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 3 PM PST THIS AFTERNOON FOR PT ARENA
TO PT REYES 10-60 NM.
GALE WARNING FROM 3 PM THIS AFTERNOON TO 3 PM 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...FLYNN
LONG TERM....FLYNN
AVIATION...KENNEDY
MARINE...FLYNN
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