476
FXUS66 KMTR 041718
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
918 AM PST TUE FEB 4 2025
..NEW UPDATE
SYNOPSIS
ISSUED AT 1202 AM PST TUE FEB 4 2025
AN ATMOSPHERIC RIVER WILL CONTINUE TO BRING HEAVY RAIN, URBAN AND
RIVER FLOODING, AND STRONG WINDS TO THE BAY AREA AND CENTRAL
COAST THROUGH TUESDAY. THERE IS ALSO AN INCREASING CHANCE FOR
THUNDERSTORMS IN THE AFTERNOON. WHILE LESS IMPACTFUL IN THE
SECOND HALF OF THE WEEK, RAIN CHANCES CONTINUE THROUGH FRIDAY.
UPDATE
ISSUED AT 918 AM PST TUE FEB 4 2025
WILL KEEP THE MORNING UPDATE A LITTLE SHORTER THAN NORMAL AS
OPERATIONS IS RATHER ACTIVE THIS MORNING A VARIETY OF IMPACTS:
FLOODING, DAMAGING WINDS, STORM FORCE OVER THE COASTAL WATERS,
ROCK SLIDES, AND THUNDERSTORM POTENTIAL THIS MORNING.
LATEST SURFACE ANALYSIS STILL SHOWS THE LINGERING STATIONARY
BOUNDARY TO THE NORTH, WHICH EXTENDS TO THE SW AND CONNECTS TO A
DEEPENING LOW PRESSURE. AS A RESULT, A MOISTURE RICH PLUME
CONTINUES TO STREAM ACROSS THE BAY AREA AND CENTRAL COAST. KMUX
RADAR IMAGERY SHOWS WIDESPREAD RAIN SHOWERS ACROSS THE REGION.
GIVEN THE RAINFALL RATES, ALREADY PRIMED STREAMS/CREEKS, AND
URBAN RUNOFF ISSUES, FLOOD ADVISORIES AND FLOOD WARNINGS HAVE BEEN
ISSUED.
THE MAIN FOCUS OF THE NEAR TERM FORECAST WILL BE THIS AFTERNOON.
THE AFOREMENTIONED LOW PRESSURE WILL RIDE ALONG THE BOUNDARY TO
THE NORTHEAST. AS THIS HAPPENS, AN UPSTREAM JET MAX WILL MOVE
EASTWARD AN INCREASE TO 150KT+. THIS MAX WILL BE PARKED RIGHT OVER
THE COASTAL WATERS WITH THE SURFACE LOW ON THE NORTHERN FRINGE.
EXPECT RAPID INCREASE IN SURFACE WINDS (SOME CAMS ARE NOW SHOWING
80-90MPH OVER THE WATERS) AND LOW LEVEL SHEAR. AS NOTED BELOW,
IT'S A LOW CAPE HIGH SHEAR SCENARIO, WHICH MAY LEAD TO SPINNING
CELLS.
IF THERE'S A PERIOD OVER THE NEXT 24 HOURS TO BE WEATHER AWARE IT
WILL BE THIS AFTERNOON. A RE-NEWED PUSH OF RAIN, WINDS, AND
POSSIBLE THUNDERSTORMS.
MM
SHORT TERM
(TODAY AND TONIGHT)
ISSUED AT 1202 AM PST TUE FEB 4 2025
SYNOPTIC OVERVIEW: A STATIONARY BOUNDARY IS DRAPED ACROSS
NORTHERN CALIFORNIA WITH LOW PRESSURE OFF THE COAST. THE BAY AREA
IS NOW IN THE CROSS-HAIRS OF THE ATMOSPHERIC RIVER. OVER THE NEXT
24 HOURS, A 150+ KT JET MAX WILL MOVE OVER THE BAY AREA/CENTRAL
COAST, CAUSING DIVERGENCE ALOFT, AND CYCLOGENESIS ALONG THE
BOUNDARY (PATTERSON'S LAW). THIS WILL ENCOURAGE AN ACTIVE COLD
FRONT TO MOVE THROUGH THE REGION, LIFTING THE WARM, MOIST AIR MASS
ON TUESDAY.
RAIN: PREFRONTAL RAIN HAS BEEN ONGOING FOR SEVERAL HOURS IN THE NORTH
BAY, AND HAS RECENTLY SPREAD SOUTH ACROSS THE BAY AREA TO THE
SANTA CRUZ MOUNTAINS. OBSERVED RAINFALL RATES HAVE BEEN AS HIGH
AS 0.64"/HR IN SAN FRANCISCO. THIS PRE-FRONTAL RAIN WILL CONTINUE
THROUGH THE EARLY MORNING. WHILE MOSTLY STRATIFORM IN THE WARM
AIRMASS, THERE ARE SOME EMBEDDED SHOWERS BRINGING STRONGER DOWN
POURS. AS THE COLD FRONT MOVES THROUGH DURING THE DAY TUESDAY, THE
RAIN RATES WILL INCREASE SIGNIFICANTLY AS THE COLD, DENSE AIR
MASS LIFTS THE WARM, MOIST AIR MASS, WRINGING OUT THE ATMOSPHERIC
SPONGE. THIS EFFECT WILL BE ENHANCED ALONG THE WINDWARD SIDE OF
THE COASTAL MOUNTAINS.
FLOODING: SEVERAL AREA FLOOD ADVISORIES ARE IN EFFECT FOR URBAN
AND SMALL STREAM FLOODING ACROSS THE NORTH BAY, SAN FRANCISCO AND
THE NORTHERN EAST BAY. THE GREEN VALLEY CREEK AT MARTINELLI ROAD
HAS REACHED MODERATE FLOOD STAGE AND CONTINUES TO RISE, VERIFYING
A FLOOD WARNING IN CENTRAL SONOMA COUNTY. IN A SIGNIFICANT CHANGE
TO THE FORECAST, THE RUSSIAN RIVER AT GUERNEVILLE IS NOW EXPECTED
TO REACH MINOR FLOOD STAGE WEDNESDAY MORNING AS MORE WATER THAN
EXPECTED HAS ENTERED THE UPPER RUSSIAN. IN ADDITIONS TO STREAMS
AND RIVERS, SEVERAL REPORTS HAVE BEEN COMING IN OF URBAN AND
ROADWAY FLOODING AS HEAVIER BANDS OF RAIN PUSH THROUGH. EXPECT
THIS TO CONTINUE THROUGH THE DAY.
WIND: THE STRONG JET MAX AND HEAVY RAIN WILL ALLOW GOOD MOMENTUM
TRANSFER DOWN TO THE SURFACE, ESPECIALLY IN GUSTS. THE WINDS LOOK
STRONGEST IN THE MONTEREY BAY REGION AND HIGHER ELEVATIONS
THROUGH THE AFTERNOON, ALTHOUGH STRONG WINDS WILL BE PRETTY
WIDESPREAD AFTER THE SUN COMES UP AND AS THE FRONT MOVES THROUGH.
THUNDERSTORMS: THIS IS THE MOST METEOROLOGICALLY INTERESTING
ASPECT OF THE SHORT FORECAST. WILL WE GET THUNDERSTORMS TOMORROW?
IS THERE A CHANCE THESE STORMS WILL ROTATE? OVERALL THE
APPROACHING AIR MASS IS NOT THAT COLD. ORIGINATING FROM A MARITIME
ENVIRONMENT, THE 1000-500 MB THICKNESS IS ONLY AROUND 546 DAM
BEHIND THE FRONT. THAT MEANS THE INSTABILITY WILL BE A LIMITING
FACTOR. EVEN WITH GOOD TIMING OF FROPA AROUND THE MAXIMUM DAY-
TIME SURFACE HEATING, THE MOST UNSTABLE CAPE VALUES ARE ONLY
EXPECTED TO REACH AROUND 50 J/KG. ON THE OTHER SIDE OF THE
INGREDIENT LIST, THE LOW LEVEL SHEAR LOOKS QUITE IMPRESSIVE. 0-1
KM SHEAR OF 35+ KTS WITH NICE, CURVED HODOGRAPHS AND LOW LCL
HEIGHTS SUGGEST THAT IF THUNDERSTORMS ARE ABLE TO TAP INTO THE
MODERATE INSTABILITY, THEY COULD START ROTATING. THE BEST WINDOW
FOR THIS IS FROM 3 PM TO 6 PM SOMEWHERE SOUTH OF SAN JOSE WHERE
THE HRRR SHOWS THE 0-1 KM HELICITY SPIKING ABOVE 300 AS THE FRONT
MOVES THROUGH. THE MARINE ENVIRONMENT WILL ALSO FAVOR SOME
RUMBLES OF THUNDER WITH A SMALL CHANCE OF WATER SPOUTS.
LONG TERM
(WEDNESDAY THROUGH MONDAY)
ISSUED AT 1202 AM PST TUE FEB 4 2025
WE WILL GET A BREAK ON WEDNESDAY, BUT IT WON'T LAST LONG. A RIDGE
WILL BRIEFLY BUILD ALLOWING THE NEW AIR MASS TO DRY OUT A BIT.
ANOTHER MOISTURE PLUME AND SURFACE LOW PRESSURE WILL ARRIVE AT
THE COAST AND PUSH INLAND ON THURSDAY. THIS SYSTEM LOOKS A GOOD
DEAL WEAKER THAN THE CURRENT ATMOSPHERIC RIVER, WITH LESS RAIN AND
LIGHTER WINDS. OUTSIDE OF THE COASTAL MOUNTAINS, MOST AREAS WILL
RECEIVE A MORE MANAGEABLE AMOUNT OF RAIN BETWEEN 1/2" TO 1". THIS
SYSTEM WILL DIVE A LITTLE FARTHER SOUTH HOWEVER, BRINGING A
REINFORCING SHOT OF COLD AIR. THE 1000-500 MB THICKNESS WILL DROP
BELOW 540 DAM. AS THINGS DRY OUT FRIDAY AND THE CLOUDS START TO
CLEAR OVER THE WEEKEND, OVERNIGHT LOWS WILL DROP BACK INTO THE
30S. SOME PLACES WILL BE MORE THAN 10 DEGREES COLDER ON SATURDAY
MORNING, COMPARED TO FRIDAY. ONCE THE DRY, COLD WEATHER SETS IN
THE PATTERN WILL STABILIZE WITH MORE OF THE SAME THROUGH EARLY
NEXT WEEK.
AVIATION
(12Z TAFS)
ISSUED AT 404 AM PST TUE FEB 4 2025
WIDESPREAD RAIN IS SPREADING INTO THE BAY AREA AND CENTRAL COAST
WITH CIGS AND VIS LOWERING RAPIDLY. SHOWERS WILL BECOME MORE
WIDESPREAD AND HEAVIER AS A SECOND ROUND OF MODERATE TO HEAVY RAIN
RETURNS 18Z TO 06Z. A LOW CHANCE OF THUNDERSTORMS EXISTS FOR
AIRPORTS SOUTH OF SFO, PARTICULARLY FOR HAF AND MRY, BUT CONFIDENCE
IS TOO LOW TO INCLUDE IN TAF. GUSTY SOUTHEAST TO SOUTHERLY WINDS
HAVE DEVELOPED AT MANY SITES ALREADY AND WILL CONTINUE TO STRENGTHEN
THROUGH THE REST OF THE MORNING. VISIBILITIES AND CIGS MAY
TEMPORARILY DROP FURTHER IF A PARTICULARLY HEAVY SHOWER MOVES
DIRECTLY OVER THE AIRPORT. CONDITIONS WILL IMPROVE BETWEEN 03-06Z AS
THE BULK OF THE RAIN WILL HAVE PASSED OUT OF THE AREA AND WINDS WILL
BE ON THE DOWNTREND.
VICINITY OF SFO...MODERATE TO AT TIMES HEAVY SHOWERS CONTINUE TO
TRAIN OVER SFO THROUGH THE MAJORITY OF THE DAY. SHOWERS MAY
TEMPORARILY LIGHTEN EARLY THIS MORNING BUT MODERATE TO HEAVY RAIN
WILL RETURN BY LATE THIS MORNING AND FURTHER REDUCE VISIBILITIES AND
CEILINGS. BY 06Z, RAIN WILL HAVE MOVED OUT OF THE VICINITY OF SFO
WITH CIGS GRADUALLY RISING AND WINDS TRENDING DOWNWARDS.
SFO BRIDGE APPROACH... SIMILAR TO SFO.
MONTEREY BAY TERMINALS...SHOWERS WILL BUILD TO CONSISTENT MODERATE
TO HEAVY RAIN BY MID TO LATE MORNING. CIGS AND VIS WILL BECOME MVFR
BUT MAY TEMPORARILY DECREASE FURTHER IF A PARTICULARLY STRONG SHOWER
MOVES DIRECTLY OVER THE SITE. GUSTY WINDS, PARTICULARLY FOR SNS,
WILL CONTINUE THROUGH MUCH OF THE DAY BEFORE WEAKENING LATE TONIGHT.
THUNDERSTORM CHANCES INCREASE AFTER 21Z AND PERSIST THROUGH 06Z BUT
CONFIDENCE IS TOO LOW TO INCLUDE IN TAF AT THIS TIME.
MARINE
(TODAY THROUGH SUNDAY)
ISSUED AT 404 AM PST TUE FEB 4 2025
WIDESPREAD BREEZY TO GUSTY WINDS CONTINUE. WINDS HAVE EASED BELOW
GALE FORCE CRITERIA ACROSS THE NORTHERN WATERS WITH GALE WARNINGS
TO BE CONVERTED TO SMALL CRAFT ADVISORIES. GALE FORCE WINDS
CONTINUE SOUTH OF POINT REYES WITH STORM FORCE WINDS EXPECTED
ALONG THE SOUTHERN INNER WATERS ALONG THE BIG SUR COAST. HIGH
RESOLUTION GUIDANCE SUGGESTS SHOWERS WILL BECOME MORE SCATTERED
IN NATURE EARLY THIS MORNING BEFORE A SECOND ROUND OF WIDESPREAD
RAIN BEGINS LATE MORNING THROUGH THIS EVENING. THUNDERSTORM
CHANCES INCREASE OVER THE COASTAL WATERS THROUGHOUT THE DAY WITH
THE HIGHEST LIKELIHOOD OVER THE SOUTHERN WATERS. EXPECT MODERATE
SIGNIFICANT WAVE HEIGHTS WITH FRESH SWELLS AND STEEP WIND WAVES
RESULTING IN HAZARDOUS MARINE CONDITIONS. ANOTHER DISTURBANCE
WILL IMPACT OUR COASTAL WATERS LATER THIS WEEK BEGINNING
THURSDAY, AND PERSISTING INTO FRIDAY.
HYDROLOGY
ISSUED AT 1202 AM PST TUE FEB 4 2025
A STRONG ATMOSPHERIC RIVER AND ACCOMPANYING SURFACE LOW IS
BRINGING HEAVY RAINFALL AND INCREASED FLOOD RISK ACROSS THE NORTH
BAY, AND THE COASTAL RANGES OF THE BAY AREA AND CENTRAL COAST
THROUGH MIDWEEK. STREAMS ARE STARTING TO FLOOD IN SONOMA COUNTY
AND THE RUSSIAN RIVER IS NOW EXPECTED TO FLOOD STAGE EARLY WEDNESDAY.
A FLOOD WATCH WILL IS IN EFFECT THROUGH 4 AM PST WEDNESDAY. THERE
IS A FLOOD WARNING FOR CENTRAL SONOMA COUNTY AS THE GREEN VALLEY
CREEK AT MARTINELLI ROAD IS NOW IN MODERATE FLOOD STAGE. SEVERAL
FLOOD ADVISORIES ARE IN EFFECT THIS MORNING WITH NUMEROUS REPORTS
OF URBAN AND SMALL STREAM FLOODING ACROSS THE NORTHERN HALF OF THE
BAY AREA. WITH A SIGNIFICANT CHANGE IN THE OVERNIGHT FORECAST,
THE RUSSIAN RIVER AT GUERNEVILLE IS NOW EXPECTED TO REACH MINOR
FLOOD STAGE BY EARLY WEDNESDAY MORNING AND A RIVER FLOOD WARNING
IS IN EFFECT.
MTR WATCHES/WARNINGS/ADVISORIES
CA...FLOOD WATCH THROUGH LATE TONIGHT FOR CAZ006-502>506-508>510-
512>518-528>530.
WIND ADVISORY UNTIL 11 PM PST THIS EVENING FOR CAZ508>510-
512>518-528>530.
PZ...SMALL CRAFT ADVISORY UNTIL 9 AM PST THIS MORNING FOR MRY BAY-SF
BAY N OF BAY BRIDGE.
GALE WARNING UNTIL 9 PM PST THIS EVENING FOR MRY BAY-SF BAY N OF
BAY BRIDGE.
SMALL CRAFT ADVISORY UNTIL 9 PM PST THIS EVENING FOR PT ARENA TO
PT REYES 0-10 NM-PT ARENA TO PT REYES 10-60 NM.
GALE WARNING UNTIL 9 PM PST THIS EVENING FOR PIGEON PT TO PT
PINOS 10-60 NM-PT REYES TO PIGEON PT 0-10 NM.
GALE WARNING UNTIL 9 AM PST THIS MORNING FOR PIGEON PT TO PT
PINOS 0-10 NM-PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM.
STORM WARNING UNTIL 9 PM PST THIS EVENING FOR PIGEON PT TO PT
PINOS 0-10 NM-PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM.
SHORT TERM...FLYNN
LONG TERM....FLYNN
AVIATION...KENNEDY
MARINE...KENNEDY
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