676
FXUS66 KMTR 010604
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1004 PM PST FRI JAN 31 2025
..NEW AVIATION, HYDROLOGY
SYNOPSIS
ISSUED AT 137 PM PST FRI JAN 31 2025
IMPACTFUL ATMOSPHERIC RIVER BEGINNING ACROSS NORTHERN AND CENTRAL
CALIFORNIA. A FLOOD WATCH IS IN EFFECT FOR THE NORTH BAY UNTIL 10
PM SUNDAY EVENING. SCATTERED SHOWERS CONTINUE TODAY, WITH HEAVIER
RAINFALL EXPECTED FOR THE NORTH BAY SATURDAY. LULL IN THE
ACTIVITY WITH LINGERING SHOWERS SUNDAY BEFORE ANOTHER PERIOD OF
IMPACTFUL RAINFALL MONDAY AND TUESDAY ACROSS THE BAY AREA AND
CENTRAL COAST.
SHORT TERM
(THIS EVENING THROUGH SATURDAY)
ISSUED AT 137 PM PST FRI JAN 31 2025
RAIN SHOWERS CONTINUE TO SPREAD ACROSS THE REGION THIS AFTERNOON
WITH RATES MOSTLY IN THE BALLPARK OF 0.1 IN/HR. OVERALL SHOULD BE
RELATIVELY QUIET THE REST OF TODAY AND TONIGHT OUTSIDE OF THE
OCCASIONAL SHOWERS. WE WILL BE LOCATED UNDER THE RIGHT EXIT REGION
OF A STRONG 150 KT JET LOCATED TO OUR NORTH INTO THIS EVENING, WHICH
WILL AIDE IN KEEPING THE LID ON THINGS FOR THE MOST PART, IN REGARD
TO HEAVY RAINFALL RATES. THE EXCEPTION TO THIS WILL BE SOME HEAVIER
SHOWERS ALONG THE COASTAL NORTH BAY DRIVEN BY A BIT OF STRONGER
FORCING ALOFT AS THE JET MEANDERS A BIT TO THE SOUTH, AND ENHANCED
BY OROGRAPHIC FORCING ALONG THE COASTLINE. IN THE ABSENCE OF
STRONGER LARGE SCALE FORCING, RAINFALL OVERNIGHT LOOKS TO BE FAIRLY
BENIGN IN TERMS OF IMPACTS.
BY MID SATURDAY MORNING, A MORE VIGOROUS SHORTWAVE IS PROGGED TO
MOVE THROUGH WITH MUCH BETTER LARGE SCALE SUPPORT IN THE RIGHT
ENTRANCE REGION OF THE UPPER LEVEL JET. THIS WILL LEAD TO ENHANCED
MOISTURE TRANSPORT AHEAD OF A STRONGER SURFACE FRONT, LEADING TO A
MORE EXTENDED PERIOD OF HIGHER RAINFALL RATES. POTENTIALLY ENOUGH TO
RESULT IN IMPACTS TO INFRASTRUCTURE, SUCH AS WATER OVER ROADWAYS,
SWOLLEN CREEKS AND DRAINAGES, AND MINOR URBAN FLOODING. THE BEST
SPATIAL ESTIMATE FOR THE CORRIDOR OF ENHANCED RAINFALL RATES LOOKS
TO BE ROUGHLY FROM THE SF BAY NORTHWARD, INCLUDING ALL OF THE NORTH
BAY REGION. IN TERMS OF SATURDAY TOTALS, LOCATIONS IN THE NORTH BAY
WILL LIKELY SEE IN THE RANGE OF 2-4", LOCALLY HIGHEST AMOUNTS IN THE
HIGHER TERRAIN AND COASTAL RANGE. AROUND THE SF BAY AREA IS MORE
LIKELY TO REMAIN BELOW 2" WITH MOST SEEING IN THE 1-2" RANGE, 2-3"
IN THE SANTA CRUZ MTNS, AND LESS THAN AN INCH IN THE RAIN SHADOWED
SANTA CLARA VALLEY.
LONG TERM
(SATURDAY NIGHT THROUGH NEXT THURSDAY)
ISSUED AT 137 PM PST FRI JAN 31 2025
SUNDAY WILL BE A TRANSITION DAY AS UPPER LEVEL SUPPORT WEAKENS OVER
THE BAY AREA AND MOVES NORTH. THIS WILL ULTIMATELY RESULT IN THE
AXIS OF ENHANCED MOISTURE WOBBLING TO THE NORTH SLIGHTLY BEFORE
MOVING BACK SOUTH AS THE UPPER LOW STRENGTHENS, MATURES, AND MOVES
SOUTHWARD OVER OUR REGION. SUNDAY AND EARLY MONDAY LOOK TO BE
COMPRISED MOSTLY OF LIGHTER SCATTERED SHOWERS, PRECLUDING THE
STRONGER FORCING WHICH IS PROGGED TO ARRIVE LATER ON MONDAY. BY
MONDAY AFTERNOON WE WILL BE UNDER WHAT WILL LIKELY BE THE BEST
OVERALL FORCING OF THE EVENT WHICH WILL PROMOTE MODERATE-TO-HEAVY
RAINFALL RATES OVER A MUCH MORE WIDESPREAD AREA RANGING FROM NORCAL
ALL THE WAY DOWN THROUGH THE CENTRAL COAST. THIS PERIOD OF INTEREST
IS EXPECTED TO LAST INTO TUESDAY AFTERNOON. THERE IS A WINDOW FOR A
SLIGHT CHANCE OF THUNDERSTORMS TUESDAY MORNING AS WELL, MAINLY ALONG
COASTAL AREAS ROUGHLY FROM PACIFICA TO BIG SUR. THIS MONDAY-TUESDAY
TIMEFRAME WILL LIKELY BE THE MOST IMPACTFUL, GIVEN THAT SOILS WILL
BE SATURATED BY THE RAINFALL OVER THE WEEKEND WITH COMPOUNDING
IMPACTS. CONDITIONS ARE A BIT LESS WORRISOME IN REGARD TO FLOODING
ALONG THE CENTRAL COAST WHERE SOILS WILL HAVE NOT RECEIVED AS
MUCH RAINFALL AS OTHER LOCATIONS THIS WEEKEND, SUCH AS THE NORTH
BAY.
CUT OFF FROM MUCH OF THE UPPER LEVEL STEERING PATTERN, THIS STRONG
STORM SYSTEM IS EXPECTED TO LINGER AROUND THE REGION THROUGH MUCH OF
THE UPCOMING WEEK. WHILE WE AREN'T IDENTIFYING ANY OTHER PERIODS OF
PERSISTENT HEAVIER RAINFALL OTHER THAN THE AFOREMENTIONED SATURDAY
AND MONDAY/TUESDAY TIMEFRAMES, LINGERING SHOWERS WILL LIKELY STAY
WITH US THROUGH AT LEAST THURSDAY.
REFER TO THE HYDROLOGY SECTION BELOW FOR MORE INFORMATION ABOUT
FLOODING POTENTIAL FOR VARIOUS RIVERS AND STREAMS.
AVIATION
(06Z TAFS)
ISSUED AT 1003 PM PST FRI JAN 31 2025
RAIN HAS BRIEFLY EASED THIS EVENING, THOUGH CIGS HAVE STAYED AROUND
MVFR OR LOWER FOR MAJORITY OF THE SITES. A FEW AREAS IN THE NORTH
BAY ARE REPORTING LOWER VISIBILITIES AS WELL EITHER DUE TO FOG OR
LIGHT RAIN. EXPECT VISIBILITY TO FLUCTUATE BETWEEN VFR TO IFR AND BE
HEAVILY DEPENDENT ON HOW HEAVY THE RAIN IS. TIMING OF THAT WILL
LIKELY BE DIFFICULT AND MAY NEED TO BE ADDED AT A LATER POINT WITH
SOME TEMPOS. BUT FOR NOW, THE TAFS GENERALLY PROVIDE A RATHER
PESSIMISTIC FORECAST OF MVFR TO IFR/LIFR CONDITIONS PREVAILING. IN
ADDITION TO THE RAIN, GUSTY SOUTHERLY WINDS OF 10-15KT WITH GUSTS UP
TO 25KT ARE EXPECTED AT MOST SITES, ESPECIALLY BY SATURDAY
AFTERNOON.
VICINITY OF SFO...NO MAJOR CHANGES TO THE FORECAST OTHER THAN THE
GUSTY SOUTHERLY WIND ONSET MAY BE DELAYED BY EITHER A FEW HOURS THIS
EVENING OR LATER. SHOULD THE DELAY OCCUR, EXPECT INCREASING
SOUTHERLY WINDS BY MID TO LATE MORNING. OTHERWISE, PERIODS OF LIGHT
TO MODERATE RAIN ARE FORECAST THROUGH EARLY TOMORROW AFTERNOON. THE
PERIODS OF WILL LIKELY LEAVE SFO WITH PREVAILING MVFR CONDITIONS,
WITH POCKETS OF IFR OR LOWER BEING POSSIBLE IF A HEAVIER BAND OF
RAIN MOVES OVER THE REGION. THERE MAY BE BREAK IN THE RAIN TOMORROW
AFTERNOON, WITH PERHAPS SOME VICINITY SHOWERS SKIRTING BY BETWEEN
2200-0400Z. SHOWERS ARE EXPECTED TO RETURN AFTER THAT.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...LIGHT SHOWERS HAVE STARTED TO MOVE INTO THE
REGION, GRACING MONTEREY BAY AREA TERMINALS WITH MVFR TO IFR
CONDITIONS. EXPECT THIS TO CONTINUE TROUGH THE TAF CYCLE, WITH LIFR
CONDITIONS BEING POSSIBLE IN HEAVIER BANDS OF RAIN. GUSTY SOUTHERLY
WINDS OF 10-15KT WITH GUSTS UP TO 25KT POSSIBLE AFTER 18Z.
MARINE
(TONIGHT THROUGH NEXT WEDNESDAY)
ISSUED AT 137 PM PST FRI JAN 31 2025
WINDS HAVE BEGUN TO INCREASE THIS MORNING AS THE FIRST OF
NUMEROUS ROUNDS OF RAINFALL HAS ARRIVED ACROSS OUR COASTAL WATERS.
THE UNSETTLED PATTERN WILL CONTINUE THROUGH THE WEEKEND INTO AT
LEAST THE MIDDLE OF NEXT WEEK. HAZARDOUS MARINE CONDITIONS WILL
PERSIST WITH FRESH SWELLS AND STEEP WIND WAVES.
HYDROLOGY
ISSUED AT 1003 PM PST FRI JAN 31 2025
LIGHT TO MODERATE RAINFALL WILL RESULT IN AN INCREASED RISK FOR
RAPID RISES IN NORTH BAY RIVERS AND THE ASSOCIATED CREEKS AND
STREAMS. THE FIRST SIGNIFICANT ATMOSPHERIC RIVER OF THE CALENDAR
YEAR IS FORECAST TO IMPACT CALIFORNIA OVER THE NEXT 5 DAYS. WHILE
UNCERTAINTY EXISTS, THE PROBABILITIES OF EXCEEDING FLOOD THRESHOLDS
HAVE INCREASED ACROSS SEVERAL RIVERS IN THE NORTH BAY. THE CURRENT
FORECAST BRINGS UNSETTLED WEATHER ALONG WITH PERIODS OF LIGHT TO
MODERATE RAINFALL TO THE REGION THROUGH FRIDAY OF NEXT WEEK WITH THE
GREATEST IMPACTS EXPECTED OVER THE NORTH BAY. THE FIRST STORM THAT
IS CURRENTLY MOVING INTO THE NORTH BAY IS EXPECTED TO PRIME THE
SOILS OVER THE WEEKEND RESULTING IN QUICKER AND MORE NOTEWORTHY
RISES OF AREA STREAMS AND CREEKS FOR THE SECOND ROUND OF RAIN THAT
IS PROGGED TO IMPACT THE NORTH BAY MONDAY INTO TUESDAY. THE HIGHER
ELEVATIONS OF THE NORTH BAY WILL LIKELY ACCUMULATE AROUND 8 TO 9
INCHES OF (STORM TOTAL) PRECIPITATION WHILE NORTH BAY VALLEYS WILL
LIKELY ACCUMULATE AROUND 4 TO 6 INCHES OF (STORM TOTAL)
PRECIPITATION. SHALLOW LANDSLIDES WILL BE POSSIBLE IN COASTAL AREAS
OF THE NORTH BAY. THE THREAT WILL EXTEND SOUTHWARD TO HIGHER
ELEVATIONS OF THE BAY AREA, PARTICULARLY THE SANTA CRUZ MOUNTAINS BY
TUESDAY.
DETERMINISTIC FORECASTS KEEP MAINSTEM RIVERS BELOW FLOOD STAGE;
HOWEVER, THE EXCEEDANCE PROBABILITIES (OF RISING ABOVE FLOOD STAGE)
FOR REACHING FLOOD THRESHOLDS ARE INCREASING TUESDAY AND WEDNESDAY
ACROSS THE NORTH BAY. THE RUSSIAN RIVER AT GUERNEVILLE - GUEC1 HAS A
36% PROBABILITY OF EXCEEDING ACTION/MONITOR STAGE AND A 32%
PROBABILITY OF EXCEEDING MINOR FLOOD STAGE. SHEC1 - NAPA NEAR SAINT
HELENA HAS A 27% PROBABILITY OF EXCEEDING ACTION/MONITOR STAGE AND A
16% PROBABILITY OF EXCEEDING MINOR FLOOD STAGE. APCC1 - NAPA NEAR
NAPA HAS A 30% PROBABILITY OF EXCEEDING ACTION/MONITOR STAGE AND A
16% PROBABILITY OF EXCEEDING MINOR FLOOD STAGE. OTHER POINTS THAT
SHOW A HIGH PROBABILITY OF REACHING ACTION/MONITOR OR MINOR FLOOD
STAGE ARE: CTIC1 - LAGUNA DE SANTA ROSA AT STONY POINT ROAD NEAR
COTATI HAS A 93% PROBABILITY OF REACHING ACTION/MONITOR STAGE AND A
70% PROBABILITY OF REACHING MINOR FLOOD STAGE, MWEC1 - MARK WEST
CREEK AT MIRABEL HEIGHTS HAS A GREATER THAN 98% PROBABILITY OF
REACHING ACTION/MONITOR STAGE AND A 43% PROBABILITY OF REACHING
MINOR FLOOD STAGE, AND GEYC1 - RUSSIAN RIVER AT GEYSERVILLE HAS A
50% PROBABILITY OF REACHING ACTION/MONITOR STAGE AND A 36%
PROBABILITY OF REACHING MINOR FLOOD STAGE.
MTR WATCHES/WARNINGS/ADVISORIES
CA...FLOOD WATCH THROUGH SUNDAY EVENING FOR CAZ006-502>506-508>510-
512>515-529.
PZ...SMALL CRAFT ADVISORY UNTIL 3 AM PST SATURDAY FOR SF BAY N OF BAY
BRIDGE.
SMALL CRAFT ADVISORY UNTIL 9 AM PST SATURDAY FOR MRY BAY.
SMALL CRAFT ADVISORY UNTIL 3 PM PST SATURDAY FOR PIGEON PT TO PT
PINOS 0-10 NM-PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM-PT
REYES TO PIGEON PT 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 3 AM PST SUNDAY FOR PIGEON PT TO PT
PINOS 10-60 NM.
SHORT TERM...BEHRINGER
LONG TERM....BEHRINGER
AVIATION...KR
MARINE...KR
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