458  
FXUS66 KMTR 202359  
AFDMTR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN FRANCISCO CA  
359 PM PST FRI DEC 20 2024  
   
..NEW AVIATION  
 
   
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  
 
(00Z TAFS)  
ISSUED AT 344 PM PST FRI DEC 20 2024  
 
EXPECT VFR TO PERSIST THROUGH THE EARLY EVENING HOURS AS A STORM  
SYSTEM BEGINS TO IMPACT OUR AREA THROUGH THE OVERNIGHT INTO  
SATURDAY. MVFR/IFR CEILINGS WILL EVENTUALLY DEVELOP AFTER MIDNIGHT  
TONIGHT AND PERSIST THROUGH THE REMAINDER OF THE TAF PERIOD FOR  
OUR NORTH BAY AND BAY AREA TERMINALS.  
 
VICINITY OF SFO...VFR UNTIL LATER THIS EVENING AS CEILINGS BEGIN  
TO DROP INTO MVFR/IFR LATER TONIGHT AND PERSIST THROUGH THE  
REMAINDER OF THE TAF PERIOD. PERIODS OF LIGHT RAIN CAN BE EXPECTED  
AFTER MIDNIGHT TONIGHT THROUGH THE DAY SATURDAY.  
 
SFO BRIDGE APPROACH...SIMILAR TO SFO.  
 
MONTEREY BAY TERMINALS...VFR CONDITIONS ARE EXPECTED UNTIL LATER  
THIS EVENING, WITH IFR CEILINGS EXPECTED DEVELOP AROUND/JUST AFTER  
MIDNIGHT. GUSTY SE WINDS ARE EXPECTED AT SNS BY SUNRISE SATURDAY  
MORNING, PERSISTING THROUGH THE REMAINDER OF THE TAF PERIOD.  
 
 
   
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 SUNDAY FOR PT ARENA TO PT  
REYES 0-10 NM-PT ARENA TO PT REYES 10-60 NM-PT PINOS TO PT  
PIEDRAS BLANCAS 0-10 NM.  
 
SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 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.  
 
 
 
 
 
SHORT TERM...BEHRINGER  
LONG TERM....BEHRINGER  
AVIATION...JM  
MARINE...MM  
 
VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO  
 
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