412
FXUS66 KMTR 202255
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
255 PM PST FRI DEC 20 2024
..NEW SYNOPSIS, SHORT TERM, LONG TERM
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.
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
(18Z TAFS)
ISSUED AT 947 AM PST FRI DEC 20 2024
1845Z UPDATE - TRENDS ARE NOT FAVORABLE FOR SJC. PUSHED LOW
VIS/CIGS THROUGH 20Z. DO SEE MINOR IMPROVEMENT ON VIS, BUT NOT
CLEARING. SOLID EAST FLOW IS KEEPING LOW LEVEL MOISTURE LOCKED IN.
LOW SUN ANGLE, LIGHT WINDS, COLDER OVERNIGHT, AMPLE LOW LEVEL
MOISTURE HAS LED TO IMPACTFUL FOG/LOW CIGS FOR THE BAY AREA THIS
MORNING, ESPECIALLY SFO/SJC. HIGH CLOUDS AND LIGHT WINDS HAS LED
TO A SLOW CLEARING/IMPROVEMENT. DO EXPECT SOME IMPROVEMENT BASED
ON TRENDS/GUIDANCE THROUGH 19Z. HOWEVER, GIVEN BROADER SATELLITE
PICTURE AND FLOW PATTERN WOULD NOT BE SURPRISED ONE BIT IF
PORTIONS OF THE N AND E BAY DIDN'T CLEAR MUCH OR AT ALL THROUGH
THE AFTERNOON. FOR TONIGHT, THE NEXT STORM APPROACHES FROM THE NW
LOWERING CIGS AND BRING -RA BACK TO THE REGION. SATURDAY AM RUSH
WILL BE IMPACTED WITH PRECIP AND LOWER CIGS. CONFIDENCE IS LOW TO
MEDIUM.
VICINITY OF SFO...NEAR TERM - CIGS THAT REDEVELOPED WILL LINGER
1830-19Z. SATELLITE DOES SHOW EDGE OF CLOUD DECK E OF THE
TERMINAL TRACKING WESTWARD. EXPECTING BETTER CONDITIONS THIS
AFTERNOON WITH VFR.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...VFR. IFR CONDITIONS DEVELOP SATURDAY AM
WITH GUSTY SE WINDS AT SNS.
MARINE
(TODAY THROUGH WEDNESDAY)
ISSUED AT 947 AM PST FRI DEC 20 2024
A STORM SYSTEM OFF THE WILL BRING DETERIORATING CONDITIONS OVER
THE COASTAL WATERS FRIDAY INTO SATURDAY. THE STORM WILL BRING
RAIN, THUNDERSTORMS, INCREASING WINDS AND BUILDING SWELL.
OCCASIONAL GALE FORCE GUSTS NORTH OF POINT REYES ON SATURDAY.
WAVE HEIGHTS WILL REMAIN ELEVATED THROUGH LATE NEXT WEEK WITH 15
TO 20 FEET WAVES MONDAY THROUGH WEDNESDAY. PERSISTENT DANGEROUS
CONDITIONS FOR SMALL CRAFTS ARE EXPECTED FRIDAY INTO NEXT WEEK.
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 UNTIL 3 PM PST SATURDAY FOR PT ARENA TO PT
REYES 0-10 NM-PT ARENA TO PT REYES 10-60 NM.
SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 3 PM PST SATURDAY
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 SATURDAY FOR PT PINOS TO PT
PIEDRAS BLANCAS 0-10 NM.
SHORT TERM...BEHRINGER
LONG TERM....BEHRINGER
AVIATION...MM
MARINE...MM
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