162
FXUS66 KMTR 011145
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
345 AM PST SAT FEB 1 2025
..NEW AVIATION, MARINE
SYNOPSIS
ISSUED AT 317 AM PST SAT FEB 1 2025
IMPACTFUL ATMOSPHERIC RIVER CONTINUES ACROSS NORTHERN AND CENTRAL
CALIFORNIA. A FLOOD WATCH IS IN EFFECT FOR THE BAY AREA UNTIL 10
PM SUNDAY EVENING. SCATTERED SHOWERS WILL INCREASE IN INTENSITY BY
LATE MORNING BEFORE LIGHTENING OVERNIGHT. LIGHT SHOWERS WILL
CONTINUE ON SUNDAY BEFORE ANOTHER ROUND OF IMPACTFUL RAINFALL
BEGINS MONDAY AND TUESDAY ACROSS THE BAY AREA AND CENTRAL COAST.
SHORT TERM
(TODAY AND TONIGHT)
ISSUED AT 317 AM PST SAT FEB 1 2025
RAIN HAS RETURNED TO THE BAY AREA WITH THE FIRST AR OF THE CALENDAR
YEAR BRINGING, OVER THE LAST 24 HOURS, BETWEEN 0.5"-1.0" OF RAIN TO
THE MAJORITY OF THE NORTH BAY, UP TO 0.5" ACROSS THE REST OF THE BAY
AREA, AND UP TO 0.1" ACROSS THE CENTRAL COAST. THE BULK OF THIS RAIN
FELL YESTERDAY DURING THE DAY WITH OVERNIGHT RAIN TOTALS ON THE
LOWER END (A FEW TENTHS OF AN INCH IN MOST CASES). A LOOK AT THE 00Z
SOUNDING SHOWS FAIRLY STABLE ATMOSPHERE WITH LAPSE RATES LESS THAN
6C/KM WHICH IS HELPING TO KEEP SHOWERS LIGHT AND WELL BEHAVED.
SCATTERED SHOWERS ARE EXPECTED TO CONTINUE FOR THE NEXT SEVERAL
HOURS WITH THE NEXT ROUND OF WIDESPREAD, HEAVY RAIN BEGINNING LATER
THIS MORNING (AFTER 4 AM) AS A SHORTWAVE TROUGH MOVES THROUGH THE
BAY AREA. THIS SHORTWAVE TROUGH WILL SHIFT THE AXIS OF THE MOISTURE
PLUME FARTHER SOUTH AND BRING WIDESPREAD RAIN TO THE BAY AREA AND
CENTRAL COAST. HEAVIER SHOWERS WILL TAPER OFF BY THE LATE
AFTERNOON/EVENING HOURS ACROSS THE CENTRAL COAST AND SOUTHERN
PORTIONS OF THE BAY AREA AS THE MAIN MOISTURE PLUME SHIFTS NORTHWARD
AGAIN. LIGHT, SCATTERED SHOWERS WILL PERSIST OVERNIGHT ACROSS THE
SOUTHERN BAY AREA AND CENTRAL COAST. LIGHT TO MODERATE RAIN WILL
REMAIN POSSIBLE OVER THE NORTH BAY OVERNIGHT AS THE MOISTURE PLUME
SHIFTS NORTH AGAIN. AS SUCH, RAIN TOTALS ON SATURDAY WILL BE HIGHER
WITH 1"-2" EXPECTED ACROSS THE NORTH BAY, 0.5"-1" ACROSS THE REST OF
THE BAY AREA, AND UP TO 0.5" ALONG THE CENTRAL COAST.
A FLOOD WATCH REMAINS IN EFFECT THROUGH 10 PM PST SUNDAY FOR THE
BAY AREA WITH MINOR NUISANCE FLOODING BECOMING MORE LIKELY HEADING
INTO SATURDAY AS SHOWERS RAMP UP AND HEAVIER RAIN RATES BECOME
MORE LIKELY. IT IS WORTH NOTING THAT THANKS TO THE RECENT DRY
SPELL, SOILS WERE FAIRLY DRY PRIOR TO THE START OF THIS EVENT
WHICH ALLOWED THEM TO ABSORB MORE WATER AND DECREASE SURFACE
RUNOFF. AS WE HEAD INTO DAY TWO OF THIS AR, SOILS WILL START TO
BECOME MORE SATURATED WITH RUNOFF AND FLOODING CONCERNS LIKELY TO
INCREASE THROUGHOUT THE WEEK. THIS WILL BE PARTICULARLY TRUE FOR
THE NORTH BAY WHERE THE MOST CONTINUOUS RAINFALL IS EXPECTED
THANKS TO MOISTURE TRAINING OVER THE REGION. SEE THE "HYDROLOGY"
SECTION BELOW FOR DETAILS ON ADDITIONAL FLOODING CONCERNS THIS
WEEK. ADDITIONALLY, GUSTY SOUTHERLY WINDS, PARTICULARLY ALONG THE
COAST AND ACROSS ELEVATED TERRAIN, WILL BUILD THROUGHOUT THE
WEEKEND WITH GUSTS BETWEEN 30 TO 40 MPH POSSIBLE. THE COMBINATION
OF GUSTY WINDS AND MOISTENING SOILS WILL INCREASE THE LIKELIHOOD
OF DOWNED TREES AND POWER OUTAGES THIS WEEK.
LONG TERM
(SUNDAY THROUGH FRIDAY)
ISSUED AT 317 AM PST SAT FEB 1 2025
SHOWERS ARE EXPECTED TO CONTINUE THROUGH THE REMAINDER OF THE
WEEKEND AND INTO NEXT WEEK AS AN AR CONTINUES TO IMPACT THE WEST
COAST. SUNDAY WILL ACT AS A BRIEF BREAK BETWEEN ROUNDS OF HEAVIER
RAINFALL ON SATURDAY AND MONDAY WITH LIGHTER RAIN EXPECTED
EVERYWHERE. AFTER THE PASSAGE OF SATURDAY'S SHORTWAVE TROUGH, THE
UPPER LEVEL FLOW BECOMES MORE ZONAL (REDUCING UPPER LEVEL FORCING)
AND THE SURFACE LOW PRESSURE SYSTEM SHIFTS NORTHWARD, BECOMING
STATIONARY OVER THE NORTH BAY. THIS WILL SHIFT THE MOISTURE PLUME
NORTHWARD AS WELL AND CONTINUE TO TRAIN MOISTURE OVER THE NORTH BAY
WITH LOCALLY HIGHER RAINFALL TOTALS POSSIBLE THERE. COMPARATIVELY,
THE AMOUNT OF AVAILABLE MOISTURE WILL BE REDUCED FARTHER SOUTH, WITH
FAIRLY LIGHT RAIN TOTALS ANTICIPATED OUTSIDE OF THE NORTH BAY. GIVEN
THIS, AN ADDITIONAL 1"-2" OF RAIN IS POSSIBLE OVER THE NORTH BAY, UP
TO 1" ACROSS THE BAY AREA, AND UP TO 0.25" ACROSS THE CENTRAL COAST
ON SUNDAY.
HEADING INTO MONDAY, ZONAL FLOW WILL GIVE WAY TO PERSISTENT UPPER
LEVEL TROUGHING ACROSS THE WEST COAST, KICKING OFF THE NEXT ROUND OF
MODERATE RAIN. THE SURFACE LOW PRESSURE SYSTEM WILL BECOME LESS
STATIONARY AS THE UPPER LEVEL TROUGH DEVELOPS WITH THE ASSOCIATED
MOISTURE PLUME WIDENING AND SPREADING SOUTHWARDS ON MONDAY. A COLD
FRONT ASSOCIATED WITH THIS LOW WILL PROGRESS THROUGH THE BAY AREA
AND CENTRAL COAST LATE MONDAY NIGHT INTO TUESDAY MORNING. THIS
SYSTEM WILL BRING AN ADDITIONAL 2"-4" OF RAIN TO THE NORTH BAY, 1"-
2" TO THE REST OF THE BAY AREA, UP TO 3" ACROSS THE SANTA CRUZ
MOUNTAINS AND SANTA LUCIA RANGE, AND 1"-2" ACROSS THE CENTRAL COAST.
AT THE SAME TIME, COLD FRONTAL PASSAGE WILL INCREASE ATMOSPHERIC
INSTABILITY AND BRING A 10-20% CHANCE OF ISOLATED THUNDERSTORMS OVER
THE COASTAL WATERS AND ALONG THE COASTLINE TUESDAY MORNING.
THUNDERSTORM CHANCES WILL PEAK EARLY TUESDAY MORNING BEFORE
DECREASING THROUGH THE REMAINDER OF THE DAY.
ADDITIONAL ROUNDS OF LIGHT RAIN (GENERALLY TOTALING TO BETWEEN 0.5"-
1.0") ARE EXPECTED WEDNESDAY THROUGH FRIDAY AS PERSISTENT UPPER
LEVEL TROUGHING CONTINUES OVER THE WEST COAST. GUSTY WINDS PERSIST
THROUGHOUT THE WEEK WITH COOLER MORNING TEMPERATURES RETURNING
WEDNESDAY THROUGH THE EXTENDED FORECAST. THE COMBINATION OF GUSTY
WINDS, COLD MORNINGS, AND CONTINUED WET WEATHER WILL CREATE
HAZARDOUS CONDITIONS FOR THOSE WITHOUT ADEQUATE ACCESS TO HEAT OR
SHELTER. COLD WEATHER PRODUCTS ARE LIKELY TO BE EVALUATED FOR MID
WEEK AND BEYOND AS WE GET CLOSER IN TIME TO THEM. FOR SNOW LOVERS,
IT IS WORTH NOTING THAT, IN THE WAKE OF COLD FRONTAL PASSAGE, SNOW
LEVELS WILL DROP TO BETWEEN 2500-3500 FEET FOR PORTIONS OF THE
REGION. THIS, IN COMBINATION WITH THE CONTINUED WET WEATHER,
MEANS THERE IS A NON- ZERO CHANCE FOR LIGHT SNOWFALL ON THE
HIGHEST PEAKS OF THE NORTH BAY MOUNTAINS AND IN THE SANTA LUCIA
RANGE. WHILE CONFIDENCE REMAINS LOW, PROBABILISTIC GUIDANCE DOES
SHOW A 30-40% CHANCE OF TRACE SNOWFALL ACROSS THE PEAKS OF THE
NORTH BAY MOUNTAIN MID TO LATE WEEK. THIS IS STILL SEVERAL DAYS
OUT AND THE FORECAST IS LIKELY TO CHANGE, BUT, IT MAY BE WORTH
KEEPING AN EYE ON THE CAL ALERT CAMERAS LATE WEEK TO SEE IF YOU
CAN SPOT ANY MOUNTAIN SNOWFALL.
LONG TERM
(SUNDAY THROUGH FRIDAY)
ISSUED AT 317 AM PST SAT FEB 1 2025
SHOWERS ARE EXPECTED TO CONTINUE THROUGH THE REMAINDER OF THE
WEEKEND AND INTO NEXT WEEK AS AN AR CONTINUES TO IMPACT THE WEST
COAST. SUNDAY WILL ACT AS A BRIEF BREAK BETWEEN ROUNDS OF HEAVIER
RAINFALL ON SATURDAY AND MONDAY WITH LIGHTER RAIN EXPECTED
EVERYWHERE. AFTER THE PASSAGE OF SATURDAY'S SHORTWAVE TROUGH, THE
UPPER LEVEL FLOW BECOMES MORE ZONAL (REDUCING UPPER LEVEL FORCING)
AND THE SURFACE LOW PRESSURE SYSTEM SHIFTS NORTHWARD, BECOMING
STATIONARY OVER THE NORTH BAY. THIS WILL SHIFT THE MOISTURE PLUME
NORTHWARD AS WELL AND CONTINUE TO TRAIN MOISTURE OVER THE NORTH BAY
WITH LOCALLY HIGHER RAINFALL TOTALS POSSIBLE THERE. COMPARATIVELY,
THE AMOUNT OF AVAILABLE MOISTURE WILL BE REDUCED FARTHER SOUTH, WITH
FAIRLY LIGHT RAIN TOTALS ANTICIPATED OUTSIDE OF THE NORTH BAY. GIVEN
THIS, AN ADDITIONAL 1"-2" OF RAIN IS POSSIBLE OVER THE NORTH BAY, UP
TO 1" ACROSS THE BAY AREA, AND UP TO 0.25" ACROSS THE CENTRAL COAST
ON SUNDAY.
HEADING INTO MONDAY, ZONAL FLOW WILL GIVE WAY TO PERSISTENT UPPER
LEVEL TROUGHING ACROSS THE WEST COAST, KICKING OFF THE NEXT ROUND OF
MODERATE RAIN. THE SURFACE LOW PRESSURE SYSTEM WILL BECOME LESS
STATIONARY AS THE UPPER LEVEL TROUGH DEVELOPS WITH THE ASSOCIATED
MOISTURE PLUME WIDENING AND SPREADING SOUTHWARDS ON MONDAY. A COLD
FRONT ASSOCIATED WITH THIS LOW WILL PROGRESS THROUGH THE BAY AREA
AND CENTRAL COAST LATE MONDAY NIGHT INTO TUESDAY MORNING. THIS
SYSTEM WILL BRING AN ADDITIONAL 2"-4" OF RAIN TO THE NORTH BAY, 1"-
2" TO THE REST OF THE BAY AREA, UP TO 3" ACROSS THE SANTA CRUZ
MOUNTAINS AND SANTA LUCIA RANGE, AND 1"-2" ACROSS THE CENTRAL COAST.
AT THE SAME TIME, COLD FRONTAL PASSAGE WILL INCREASE ATMOSPHERIC
INSTABILITY AND BRING A 10-20% CHANCE OF ISOLATED THUNDERSTORMS OVER
THE COASTAL WATERS AND ALONG THE COASTLINE TUESDAY MORNING.
THUNDERSTORM CHANCES WILL PEAK EARLY TUESDAY MORNING BEFORE
DECREASING THROUGH THE REMAINDER OF THE DAY.
ADDITIONAL ROUNDS OF LIGHT RAIN (GENERALLY TOTALING TO BETWEEN 0.5"-
1.0") ARE EXPECTED WEDNESDAY THROUGH FRIDAY AS PERSISTENT UPPER
LEVEL TROUGHING CONTINUES OVER THE WEST COAST. GUSTY WINDS PERSIST
THROUGHOUT THE WEEK WITH COOLER MORNING TEMPERATURES RETURNING
WEDNESDAY THROUGH THE EXTENDED FORECAST. THE COMBINATION OF GUSTY
WINDS, COLD MORNINGS, AND CONTINUED WET WEATHER WILL CREATE
HAZARDOUS CONDITIONS FOR THOSE WITHOUT ADEQUATE ACCESS TO HEAT OR
SHELTER. COLD WEATHER PRODUCTS ARE LIKELY TO BE EVALUATED FOR MID
WEEK AND BEYOND AS WE GET CLOSER IN TIME TO THEM. FOR SNOW LOVERS,
IT IS WORTH NOTING THAT, IN THE WAKE OF COLD FRONTAL PASSAGE, SNOW
LEVELS WILL DROP TO BETWEEN 2500-3500 FEET FOR PORTIONS OF THE
REGION. THIS, IN COMBINATION WITH THE CONTINUED WET WEATHER,
MEANS THERE IS A NON- ZERO CHANCE FOR LIGHT SNOWFALL ON THE
HIGHEST PEAKS OF THE NORTH BAY MOUNTAINS AND IN THE SANTA LUCIA
RANGE. WHILE CONFIDENCE REMAINS LOW, PROBABILISTIC GUIDANCE DOES
SHOW A 30-40% CHANCE OF TRACE SNOWFALL ACROSS THE PEAKS OF THE
NORTH BAY MOUNTAIN MID TO LATE WEEK. THIS IS STILL SEVERAL DAYS
OUT AND THE FORECAST IS LIKELY TO CHANGE, BUT, IT MAY BE WORTH
KEEPING AN EYE ON THE CAL ALERT CAMERAS LATE WEEK TO SEE IF YOU
CAN SPOT ANY MOUNTAIN SNOWFALL.
AVIATION
(12Z TAFS)
ISSUED AT 345 AM PST SAT FEB 1 2025
CONDITIONS ARE MAINLY A MIX OF IFR AND MVFR IN A DEEP SUBTROPICAL
MOISTURE TAP OVER THE FORECAST AREA. PERIODIC LIGHT TO MODERATE
RAIN CONTINUES ALONG WITH SOUTHERLY SURFACE WINDS OCCASIONALLY
BECOMING GUSTY TODAY. TEMPO MODERATE TO HEAVY RAIN DEVELOPING
LATER THIS MORNING OVER THE BAY AREA WITH STRENGTHENING LOWER
LEVEL WARM AIR TEMPERATURE ADVECTION.
VICINITY OF SFO...MAINLY MVFR WITH PERIODIC RAIN, INCLUDING TEMPO
MODERATE RAIN 15Z-19Z TODAY. SOUTHEAST TO SOUTH WIND OCCASIONALLY
GUSTING TO 20 KNOTS MAINLY DURING LATE MORNING AND AFTERNOON.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...MVFR-VFR WITH PERIODIC LIGHT RAIN.
VARIABLE WINDS BECOMING SOUTHEAST OCCASIONALLY GUSTING TO 15 TO 20
KNOTS TODAY, WINDS DECREASING TO 5 TO 10 KNOTS TONIGHT AND SUNDAY
MORNING.
MARINE
(TODAY THROUGH THURSDAY)
ISSUED AT 332 AM PST SAT FEB 1 2025
A DEEP SUBTROPICAL MOISTURE TAP WILL CONTINUE TO RESULT IN LIGHT
TO OCCASIONAL MODERATE RAIN OVER THE COASTAL WATERS AND BAYS
TODAY. A COLD FRONT OVER FAR NORTHERN CALIFORNIA WILL GRADUALLY
MOVE SOUTH AND MERGE WITH THE NORTHERN BOUNDARY OF SUBTROPICAL
MOISTURE DURING THE WEEKEND AND MONDAY. BY LATER MONDAY AND
TUESDAY HEAVY RAIN WILL DEVELOP ALONG A SOUTHEASTWARD MOVING COLD
FRONT. OCCASIONAL GUSTY SOUTHWEST TO SOUTH WINDS ARE LIKELY OVER
THE OUTER AND INNER CENTRAL WATERS TODAY, TONIGHT AND SUNDAY.
WINDS SHIFTING TO NORTHWEST WITH A COLD FRONTAL PASSAGE MONDAY
NIGHT AND TUESDAY.
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%
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 PM PST SUNDAY FOR PIGEON PT TO PT
PINOS 0-10 NM-PIGEON PT TO PT PINOS 10-60 NM-PT REYES TO
PIGEON PT 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 3 PM PST THIS AFTERNOON FOR PT PINOS
TO PT PIEDRAS BLANCAS 0-10 NM.
SHORT TERM...KENNEDY
LONG TERM....KENNEDY
AVIATION...CANEPA
MARINE...CANEPA
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