303
FXUS66 KMTR 210550
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
950 PM PST FRI DEC 20 2024
..NEW AVIATION, MARINE
SYNOPSIS
ISSUED AT 116 PM PST FRI DEC 20 2024
CLOUDY CONDITIONS THROUGH TODAY, SOGGY PATTERN STARTING TOMORROW
THROUGH CHRISTMAS WEEK AS A PARADE OF STORMS MOVE THROUGH THE
PACIFIC.
UPDATE
ISSUED AT 712 PM PST FRI DEC 20 2024
WHILE THE COLD FRONT OFFSHORE HAS BEEN PRODUCING SUBSTANTIAL
LIGHTNING ACTIVITY, THE RECENT NORTHWARD SHIFT HAS DECREASED
THUNDERSTORM POTENTIAL IN THE BAY AREA TOMORROW. ADEQUATE DEEP
SHEAR IS STILL EXPECTED, BUT THE INSTABILITY IS LACKING WITH LOW
LEVEL LAPSE RATES PEAKING AROUND 7 C/KM IN THE LATEST CAMS. THIS
SHOULD KEEP ANY THUNDERSTORM ACTIVITY FOCUSED OVER THE WATER. THE
OTHER UPDATE IS TO THE REMARKABLE STRENGTH OF THE STORMS OVER THE
PACIFIC. THE LATEST SATELLITE DATA HAS FOUND SEAS WELL OVER 40
FEET WITH BOTH SYSTEMS AND A HUGE AREA OF HURRICANE FORCE WINDS
ASSOCIATED WITH THE CENTRAL PACIFIC STORM. THE WAVES GENERATED
FROM THESE STORMS WILL BEGIN TO REACH THE COAST TOMORROW MORNING
AND PEAK ON MONDAY WHEN BREAKING WAVE HEIGHTS WILL LIKELY EXCEED
30 FEET.
SHORT TERM
(THIS EVENING THROUGH SATURDAY)
ISSUED AT 116 PM PST FRI DEC 20 2024
CLOUDY SKIES PERSIST THROUGH THIS EVENING AS THE FIRST WAVE IN A
SERIES OF STORM SYSTEMS ACROSS THE PACIFIC MOVES INTO THE REGION.
MOISTURE INCREASES THROUGH TONIGHT AND SATURDAY WILL START OFF
SOGGY FOR THE NORTH BAY. RAINFALL IS EXPECTED TO SPREAD SOUTHWARD
ACROSS THE REST OF THE AREA THROUGH THE DAY. THIS FIRST ROUND OF
RAINFALL SATURDAY IS EXPECTED TO BE LARGELY NON-IMPACTFUL FOR MOST
LOCATIONS OUTSIDE OF NUISANCE FLOODING IN THE NORTH BAY. SCATTERED
SHOWERS WILL CONTINUE TO LINGER INTO SUNDAY MORNING. BY THAT TIME,
THE NORTH BAY WILL HAVE SEEN 0.5-1.0", WHILE MOST OTHER LOCATIONS
SOUTH WILL BE CLOSER TO THE 0.1-0.25" RANGE. RAIN SHADOWED INLAND
LOCATIONS IN THE CENTRAL COAST REGION WILL BE LUCKY TO GET A
HUNDREDTH OF TWO OUT OF THE FIRST ROUND SATURDAY. INCREASING WINDS
SATURDAY MORNING AS THE FRONT APPROACHES WILL LIKELY BE AN ISSUE
TO WEAKENED FOLIAGE FROM LAST WEEKEND. WHILE LIKELY NOT STRONG
ENOUGH WINDS TO TOPPLE TREES AND BREAK BRANCHES ALONE, 25-35 MPH
SATURDAY MORNING WILL CERTAINLY BE ENOUGH TO BRING DOWN TREES AND
BRANCHES THAT WERE SUFFICIENTLY DAMAGED DURING LAST WEEKEND'S
STORM. IT'S THE TIME OF YEAR TO ALWAYS BE VIGILANT WHILE WALKING
UNDER DENSE TREE COVER NO MATTER THE CURRENT WEATHER.
LONG TERM
(SUNDAY THROUGH NEXT THURSDAY)
ISSUED AT 116 PM PST FRI DEC 20 2024
SOGGY WEATHER CONTINUES THROUGH THE EXTENDED PERIOD WITH SEVERAL
WAVES OF OPEN UPPER LEVEL LOWS ROTATING AROUND A DEEP PARENT LOW
IN THE GULF OF ALASKA. NEARLY ALL EXHIBIT A PSEUDO-AR TYPE
MOISTURE FLOW, BUT THE THREAT OF A CLASSIC, STATIONARY AR APPEARS
LOW AT THIS POINT. HOWEVER, WITH A SOLID MOISTURE SOURCE AND
PERSISTENT LOW-TO-MID LEVEL ONSHORE FLOW, MANY AREAS INCLUDING THE
NORTH BAY AND COASTAL RANGES IN THE BAY AREA AND CENTRAL COAST ARE
MORE LIKELY TO SEE COMPOUNDING EFFECTS DUE TO SATURATING SOILS AND
NOT HAVING MUCH TIME TO DRY OUT BETWEEN STORM SYSTEMS OVER THE
NEXT 7 DAYS. BASED ON THE CURRENT GUIDANCE, IT LOOKS LIKE THE MOST
IMPACTFUL PERIOD COMING UP IN THE NEAR-MEDIUM TERM WILL BE THE
PERIOD FROM MONDAY EVENING THROUGH TUESDAY MORNING. THIS IS WHEN A
STRONGER JET ALOFT FOCUSES MORE ON THE BAY AREA REGION PROVIDING
HIGHER RAINFALL RATES THAT WOULD MORE LIKELY LEAD TO LOCAL
FLOODING. A RELATIVE LULL IN THE ACTIVITY LOOKS LIKELY RIGHT
AROUND CHRISTMAS DAY, THOUGH STILL HOLDING ON TO ROBUST MOISTURE
TRANSPORT THANKS TO THE PARENT LOW UP IN THE GULF OF ALASKA.
ANOTHER WAVE PROGGED TO IMPACT THE REGION WEDNESDAY NIGHT INTO
THURSDAY LOOKS TO BE THE STRONGEST OF THE FORECAST PERIOD, BUT
WILL NEED TO WAIT TO TALK SPECIFICS ON THAT FOR NOW. TWO IMPORTANT
THINGS TO NOTE WHEN THINKING ABOUT THE IMPACTS FROM THAT SYSTEM
WILL BE HOW THE PARENT LOW EVOLVES INTO EARLY NEXT WEEK (WILL
AFFECT WHO GETS THE BRUNT OF IT), AND HOW MUCH RAIN CERTAIN
LOCATION RECEIVE THIS WEEKEND AND EARLY NEXT WEEK (ANTECEDENT
CONDITIONS AFFECTING RUN OFF).
AVIATION
(06Z TAFS)
ISSUED AT 932 PM PST FRI DEC 20 2024
MVFR/IFR CEILINGS EXPECTED OVER THE BAY AREA TERMINALS AND SHOULD
PREVAIL THROUGH THE REMAINDER OF THE TAF PERIOD, WITH THE
REMAINDER OF OUR SITES EXPECTED TO FOLLOW SUIT DURING THE
OVERNIGHT HOURS, WITH THE EXCEPTION OF KLVK WHICH IS CURRENTLY
FORECASTED TO REMAIN VFR.
VICINITY OF SFO...MVFR/IFR ARE EXPECTED TO PERSIST THROUGH THE
THE TAF PERIOD. PERIODS OF LIGHT RAIN CAN BE EXPECTED LATE DURING
THE OVERNIGHT AND THEN CONTINUE THROUGH THE DAY SATURDAY.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...MVFR CEILINGS ARE EXPECTED TO PERSIST
THROUGH THE TAF PERIOD. EXPECT GUSTY SE WINDS AT SNS BY SUNRISE
SATURDAY MORNING, THEN EASING AFTER SUNSET. LIGHT RAIN IS EXPECTED
TO BE IN THE AREA FROM LATE MORNING THROUGH AT LEAST EARLY
EVENING.
MARINE
(TONIGHT THROUGH NEXT THURSDAY)
ISSUED AT 932 PM PST FRI DEC 20 2024
SOUTHERLY WINDS WINDS HAVE BEGUN TO INCREASE OVER COASTAL WATER
THIS EVENING AS A STORM SYSTEM CONTINUES TO MOVE CLOSER TO THE
CALIFORNIA COAST. ONCE THE STORM MOVES ONSHORE, IT WILL BE
FOLLOWED BY A COLD FRONT THAT BEGINS TO SWEEP THROUGH EARLY
TOMORROW MORNING BRINGING RAIN, ISOLATED THUNDERSTORMS, GUSTY
WINDS, AND BUILDING SWELL. EXPECT PERIODS OF GALE FORCE GUSTS TO
DEVELOP NORTH OF POINT REYES OVERNIGHT, THEN SPREADING SOUTH BY
SUNRISE OVER THE WATERS OFF OF THE SF PENINSULA. WAVE HEIGHTS WILL
REMAIN ELEVATED THROUGH LATE NEXT WEEK WITH 15 TO 20 FOOT WAVES
MONDAY THROUGH WEDNESDAY. EXPECT DANGEROUS CONDITIONS FOR SMALL
CRAFTS THROUGH THE WEEKEND INTO THE BEGINNING OF NEXT WEEK. THE
ELEVATED SEAS WILL CONTINUE TO PRODUCE ENHANCED SHOALING AT HARBOR
ENTRANCES AND BARS.
BEACHES
ISSUED AT 350 AM PST FRI DEC 20 2024
ELEVATED SURF OF 15 TO 18 FEET, WITH OCCASIONAL BREAKERS UP TO 20
FEET, WILL OCCUR SATURDAY MORNING TO SUNDAY AFTERNOON AS ANOTHER
SYSTEM APPROACHES THE WEST COAST, WITH A HIGH SURF ADVISORY
ISSUED FOR THE PACIFIC COAST FROM 6 AM SATURDAY THROUGH 4 PM
SUNDAY.
THEN, A VERY LARGE AND POWERFUL, LONG PERIOD WEST SWELL TRAIN WILL
LIKELY ARRIVE ALONG OUR ENTIRE COASTLINE MONDAY INTO TUESDAY NEXT
WEEK. CURRENT GLOBAL WAVE MODELS ARE FORECASTING SWELL HEIGHTS TO
20+ FEET WITH VERY ENERGETIC SWELL PERIODS OF 20+ SECONDS, THIS WILL
LEAD TO MUCH HIGHER BREAKERS INCLUDING LOCALIZED COASTAL FLOODING
IMPACTS. STAY TUNED FOR FURTHER UPDATES.
MTR WATCHES/WARNINGS/ADVISORIES
CA...HIGH SURF ADVISORY FROM 6 AM SATURDAY TO 4 PM PST SUNDAY FOR
CAZ006-505-509-529-530.
PZ...SMALL CRAFT ADVISORY FROM 9 AM TO 3 PM PST SATURDAY FOR SF BAY N
OF BAY BRIDGE.
SMALL CRAFT ADVISORY FROM 3 PM SATURDAY TO 3 AM PST MONDAY FOR
MRY BAY.
SMALL CRAFT ADVISORY UNTIL 3 AM PST SATURDAY FOR PT ARENA TO PT
REYES 0-10 NM.
GALE WARNING FROM 3 AM TO 9 AM PST SATURDAY FOR PT ARENA TO PT
REYES 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 3 AM PST MONDAY FOR PIGEON PT TO PT
PINOS 0-10 NM-PIGEON PT TO PT PINOS 10-60 NM-PT PINOS TO PT
PIEDRAS BLANCAS 0-10 NM-PT REYES TO PIGEON PT 0-10 NM.
GALE WARNING UNTIL 9 AM PST SATURDAY FOR PT ARENA TO PT REYES 10-
60 NM.
SHORT TERM...BEHRINGER
LONG TERM....BEHRINGER
AVIATION...JM
MARINE...JM
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