234
FXUS66 KMTR 041013
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
213 AM PST TUE FEB 4 2025
..NEW SYNOPSIS, SHORT TERM, LONG TERM, HYDROLOGY
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.
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 ENVIORNMENT 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
(00Z TAFS)
ISSUED AT 508 PM PST MON FEB 3 2025
EXPECT OVERCAST MID-LEVEL CLOUDS TOT DROP TO MVFR CIG HEIGHTS AS THE
NEST RAIN BAND ENTERS THE REGION FROM THE NORTH. BREEZY TO GUSTY
WINDS ARE EXPECTED ALONG THE COAST AND IN THE SF BAY AS THIS RAIN
BAND APPROACHES. VISIBILITIES WILL REDUCES AS THE MAIN RAIN BAND
MOVES OVER EACH TAF SITE. WIDESPREAD RAIN IS EXPECTED OVERNIGHT WITH
SOME SORT-LIVED BREAKS. RAIN RATES INCREASE INTO THE LATE MORNING ON
TUESDAY WITH SOME LOWER CIGS POSSIBLE IN THE NORTH BAY. RAINS AND
WINDS PERSIST BEYOND THE TAF PERIOD.
VICINITY OF SFO...GUSTY WINDS LAST THROUGH THE TAF PERIOD. MVFR CIGS
AND MODERATE RAIN ARRIVE INTO THE NIGHT, WITH REDUCED VISIBILITIES
EXPECTED. RAIN RATES INCREASE WHILE WINDS REDUCE SLIGHTLY INTO LATE
TUESDAY AFTERNOON. WINDS TURN SOUTHWESTERLY LATE TUESDAY AFTERNOON.
RAINS AND WINDS LINGER BEYOND THE TAF PERIOD.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...MODERATE TO BREEZY WINDS LAST INTO THE
EVENING BEFORE REDUCING. MID-LEVEL CLOUDS LOWER INTO THE NIGHT WITH
SHOWERS APPROACHING IN THE LATE NIGHT. EXPECT BREEZY SOUTHERLY WINDS
TO BUILD INTO LATE TUESDAY MORNING AS SHOWER ACTIVITY CONTINUES.
MARINE
(TONIGHT THROUGH NEXT SUNDAY)
ISSUED AT 907 PM PST MON FEB 3 2025
WIDESPREAD BREEZY TO GUSTY CONTINUE ACROSS THE WATERS AND LOOK TO
LAST THROUGH MUCH OF TUESDAY. GALE FORCE GUST LOOK TO MOVE OUT OF
THE NORTHERN WATERS IN THE EARLY MORNING, BUT WINDS WILL STILL BE
HAZARDOUS FOR SMALL CRAFT. STORM FORCE WIND LOOK TO DEVELOP
WITHIN THE SOUTHERN INNER WATERS ALONG THE BIG SUR COAST. SHOWERS
MOVE INTO THE WATERS OVERNIGHT AND BECOME WIDESPREAD FOR TUESDAY.
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...WIND ADVISORY UNTIL 1 AM PST EARLY THIS MORNING FOR CAZ006-502-
505-509.
FLOOD WATCH THROUGH LATE TONIGHT FOR CAZ006-502>506-508>510-
512>518-528>530.
WIND ADVISORY FROM 7 AM THIS MORNING TO 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 FROM 9 AM THIS MORNING TO 9 PM PST THIS EVENING FOR
MRY BAY-SF BAY N OF BAY BRIDGE.
GALE WARNING UNTIL 3 AM PST EARLY THIS MORNING 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.
SMALL CRAFT ADVISORY UNTIL 3 AM PST EARLY THIS MORNING FOR
PIGEON PT TO PT PINOS 0-10 NM.
GALE WARNING UNTIL 9 PM PST THIS EVENING FOR PIGEON PT TO PT
PINOS 0-10 NM.
GALE WARNING UNTIL 9 AM PST THIS MORNING FOR PT PINOS TO PT
PIEDRAS BLANCAS 0-10 NM.
STORM WARNING FROM 9 AM THIS MORNING TO 9 PM PST THIS EVENING
FOR PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM.
SHORT TERM...FLYNN
LONG TERM....FLYNN
AVIATION...MURDOCK
MARINE...MURDOCK
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