660
FXUS66 KMTR 101209
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
509 AM PDT SUN MAY 10 2026
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 1205 AM PDT SUN MAY 10 2026
- WARMING AND DRYING TREND WILL CONTINUE THROUGH EARLY IN THE
WEEK WITH AFTERNOON TEMPERATURES PEAKING ON MONDAY
- MODERATE RISK FOR HEAT-RELATED ILLNESSES FOR SENSITIVE
POPULATIONS ACROSS THE INTERIOR ON MONDAY
- GRADUAL COOLING TREND AND POTENTIAL UNSETTLED WEATHER FROM
MIDWEEK THROUGH LATE WEEK
SHORT TERM
ISSUED AT 1215 AM PDT SUN MAY 10 2026
(TODAY THROUGH MONDAY)
LET'S STEP BACK AND TAKE A LOOK AT THE INTERESTING LONGWAVE
PATTERN OVER THE CONUS - RIDGE OF HIGH PRESSURE COVERS CA WHICH IS
BOOKENDED BY DEEP TROUGHS ON EITHER SIDE WITH ONE NEAR THE GREAT
LAKES AND THE OTHER NEAR GULF OF AK. THE PATTERN WILL HOLD IN THE
NEAR TERM, BUT WILL SHIFT WITH A PATTERN CHANGE ON THE HORIZON,
LITERALLY. SO WHAT DOES THIS SET UP MEAN FOR THE BAY AREA? A RIDGE
OF HIGH PRESSURE IN MAY USUALLY BRINGS DRY AND MILD CONDITIONS
AND SUNDAY IS NO EXCEPTION. HOWEVER, IT'S THE DETAILS THAT MATTER.
OVERNIGHT SATELLITE IMAGERY SHOWS SOLID STRATUS ALONG THE COAST
WORKING ITS WAY INLAND. THE MARINE LAYER WILL LIKELY TOP OUT
900-1200 FEET THIS MORNING AND WILL BE THE SPOILER FOR MAX T
POTENTIAL. WOULD NOT BE SURPRISED ONE BIT IF THE MARINE LAYER WAS
ABLE TO SQUEEZE OUT SOME DRIZZLE ALONG THE COAST. MODEL GUIDANCE
HAS STRUGGLED THE LAST FEW DAYS REGARDING MAX T AND THE MARINE
LAYER INFLUENCE...SIMPLY PUT THE FORECAST WAS TOO WARM. AS SUCH,
TRENDED TEMPERATURES DOWNWARD FROM THE NBM OVER INLAND VALLEYS OR
AREAS THAT HAVE A PRONOUNCED MARINE LAYER INFLUENCE THIS
AFTERNOON. WENT COLDER BY 3-5 DEGS, BUT WORRIED IT WASN'T UNDER
CUT ENOUGH. THAT BEING SAID, DO EXPECT THE MARINE LAYER CLOUDS TO
ERODE BACK TO THE COAST BY THIS AFTERNOON WITH INLAND SUNSHINE
AND COASTAL CLOUDS. REGARDLESS, IF YOU HAVE OUTDOOR ACTIVITIES TO
CELEBRATE MOTHER'S DAY IT WILL BE PLEASANT WITH INLAND HIGHS IN
THE 70S AND 80S AND COOLER AT THE COAST IN THE 60S - BRING A
JACKET. COULD ALSO BE A TAD BREEZY THIS AFTERNOON WITH THE TEMP
DIFFERENCE FROM THE COAST TO INTERIOR. SFC PRESSURE GRADIENTS
REMAIN ONSHORE AGAIN, BUT ARE FORECAST TO BE WEAKER THAN SATURDAY
WHERE THEY PEAKED AT 4.2 MB.
SUNDAY NIGHT THROUGH MONDAY - THE CENTER OF THE UPPER RIDGE
BEGINS TO SHIFT TOWARD THE DESERT SW WHILE THE UPSTREAM TROUGH
DEEPENS AND INCHES TOWARD THE WEST COAST. DESPITE THE SHIFT,
MONDAY IS STILL ON TRACK TO BE THE WARMEST DAY OF THE FORECAST.
850 MB TEMPS PEAK AT 20-22C. MIXING THOSE TEMPS TO THE SURFACE
UNDER IDEAL CONDITIONS WOULD BRING TOASTY TEMPS. HOWEVER, WE STILL
HAVE SOME ONSHORE FLOW AND LINGERING MARINE LAYER. AS SUCH, MAX
TEMPS WILL BE TEMPERED NEAR THE COAST AND BAYS, 60S TO LOWER 80S.
FAR INTERIOR LOCATIONS WILL BE IN THE 90S LEADING TO SOME MODERATE
HEATRISK.
LONG TERM
ISSUED AT 1220 AM PDT SUN MAY 10 2026
(MONDAY NIGHT THROUGH NEXT SATURDAY)
THE CHANGE IN THE LONGWAVE PATTERN BEGINS TO UNFOLD MONDAY NIGHT
INTO TUESDAY. THE UPPER LEVEL RIDGE IS BEING REPLACED BY A ROBUST
AND ANOMALOUSLY DEEP UPPER LOW FOR MID MAY. TEMPERATURES BEGIN TO
DROP IN RESPONSE TO LOWER 500 MB HEIGHTS AND COOLER 850 MB TEMPS,
BUT STILL ABOVE NORMAL.
BY WEDNESDAY NEAR NORMAL TEMPERATURES RETURN THANKS TO THE CUT-OFF LOW
OVER THE REGION. CONFIDENCE FADES ON THE DETAILS OF THE EXACT
PLACEMENT OF THE CUT-OFF LOW...CLUSTER ANALYSIS IS SPLIT WITH
SOME FAVORING MORE ZONAL FLOW AND OTHERS FARTHER SOUTH WITH A
DEEPER LOW. REGARDLESS OF EXACT PLACEMENT, IT'S CLEAR THAT TEMPS
DROP AND AT LEAST SOME DRIZZLE IS LIKELY. A FEW MEMBERS EVEN SHOW
LIGHT SHOWERS WEDNESDAY AFTERNOON/EVENING (TSTORMS TO THE N).
ZONAL FLOW RETURNS FOR THE SECOND HALF OF THE WORK WEEK LEADING TO
REBOUNDING TEMPERATURES AND DRIER CONDITIONS.
AVIATION
(12Z TAFS)
ISSUED AT 509 AM PDT SUN MAY 10 2026
NEARLY IDEAL CONDITIONS EXIST FOR MARINE STRATUS /MVFR-IFR/ WITH
SATELLITE SHOWING FAIRLY WIDESPREAD COVERAGE ACROSS THE BAY AREA
AND NORTH CENTRAL COAST. DESPITE THAT THERE'S A STRONG 500 MB RIDGE
AND WARMTH ALOFT (00Z SATURDAY EVENING OAKLAND UPPER AIR SOUNDING
MANDATORY LEVELS ALOFT WERE NEAR 90TH PERCENTILE FOR MID MAY), THE
MARINE LAYER IS WELL DEFINED WITH AN INLAND INTRUSION SUPPORTED BY
A 2.8 SFO-SAC PRESSURE GRADIENT. TRAVIS AFB HAS HAD ONSHORE GUSTS
TO 30 KNOTS OVERNIGHT FOR EXAMPLE. THE MARINE LAYER VARIES IN DEPTH
FROM 1200 FEET TO 2000 FEET. 24 HOUR TRENDS SHOW STEADY TO SLIGHTLY
HIGHER SURFACE DEW POINT TEMPERATURES I.E. STEADY TO GREATER AMOUNT
OF WATER VAPOR TRAPPED BENEATH THE MARINE TEMPERATURE INVERSION. IN
THE DRY AIR ABOVE THE MARINE LAYER TEMPERATURE INVERSION, NOCTURNAL
RADIATIVE COOLING LIKE PREVIOUS EARLY MORNINGS IS GOOD; FORECAST
SOUNDINGS SHOW A SIMILAR VERTICAL DISTRIBUTION OF LOW WATER VAPOR/DRY
ALOFT TONIGHT AND MONDAY MORNING SUPPORTIVE OF COOLING AGAIN TONIGHT
AND MONDAY MORNING.
RUN AFTER RUN OF THE HRRR OVERNIGHT CONTINUES TO SHOW STRATUS CLOUDS
BEGINNING TO MIX OUT PRIOR TO SUNRISE, WHICH IS HIGHLY UNLIKELY TO
HAPPEN THIS EARLY. THE NAM SHOWS STRATUS LINGERING UNTIL LATE MORNING
WHICH SEEMS MORE REASONABLE. THE ACV-SFO PRESSURE GRADIENT IS CURRENTLY
3.7 MB AND IS FORECAST TO INCREASE LATER TODAY TO THE EVENING BEFORE
DECREASING OVERNIGHT, BUT THERE'S DISAGREEMENT AS TO THE STRENGTH OF
THIS GRADIENT FOR TODAY. OVERALL, IT'S A CHALLENGING FORECAST NOT ONLY
FOR THE PUBLIC SIDE AND TEMPERATURES, BUT ALSO FOR AVIATION SIDE AND
CEILINGS FORECASTS. THERE'S BEEN A STEADY APPLICATION OF NORTHWEST
WINDS OVER THE COASTAL WATERS, PRODUCING SOME COLD WATER UPWELLING
WITH SEA SURFACE TEMPS NEAR TO 3F OR 4F ABOVE MAY NORMALS.
IT'LL TAKE THE HIGHER SUN ANGLE OF MAY TO BREAK THROUGH THE STRATUS
LAYER VIA VERTICAL MIXING TODAY. CLEARING TIMES ARE MAINLY BY LATE
MORNING, THOUGH IT MAY TAKE AN HOUR OR TWO LONGER THAN THAT DEPENDING
HOW WELL THE STRATUS HOLDS TOGETHER THROUGH MORNING. FOR TONIGHT AND
MONDAY MORNING, EXPECT STRATUS INCLUDING PATCHY FOG TO DEVELOP WITH
MVFR-IFR-LIFR LATE TONIGHT AND MONDAY MORNING.
VICINITY OF SFO...STRATUS /IFR/ INTRUSION IS WELL ESTABLISHED THIS
MORNING PER SATELLITE AND SURFACE OBSERVATIONS. NEAR 100% IFR
PROBABILITY ON HREF AT LEAST EARLY THIS MORNING, MAY ALSO CORRESPOND
TO PATCHY LIGHT DRIZZLE (FROM KHAF TO KSFO TO KOAK). FOR THE TIME
BEING, 12Z SFO TAF IS FOR DRY RUNWAYS. STRATUS IFR CEILING INCREASING
TO MVFR BY LATE MORNING WITH MIX OUT BY 20Z TODAY. STRATUS /IFR/
RETURNS 07Z TONIGHT WITH STRATUS PREVAILING THROUGH MUCH OF MONDAY
MORNING. WEST WIND 10 KNOTS WITH A FEW GUSTS TO 20 KNOTS STILL POSSIBLE
THIS MORNING, OTHERWISE INCREASING WEST WIND 15 TO 25 KNOTS FROM LATE
MORNING THROUGH THE AFTERNOON TO EARLY EVENING. WEST WIND NEAR 10
KNOTS TONIGHT AND MONDAY MORNING.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...STRATUS /IFR/ COVERS THE MONTEREY PENINSULA
WITH STRATUS EXTENDING FAR INTO THE SALINAS VALLEY; THE MARINE LAYER
IS ~ 2000 FEET DEEP HERE IN THIS PART OF THE FORECAST AREA. A FEW
PATCHES OF LIGHT DRIZZLE ARE POSSIBLE DURING THE MORNING. STRATUS
/IFR/ CONDITIONS GRADUALLY IMPROVING TO MVFR BY LATE MORNING OR
EARLY AFTERNOON. STRATUS /IFR/ RETURNS TONIGHT AND MONDAY MORNING.
WEST TO NORTHWEST WINDS 5 TO 15 KNOTS.
MARINE
(TODAY THROUGH FRIDAY)
ISSUED AT 403 AM PDT SUN MAY 10 2026
MODERATE SEAS AND FRESH TO STRONG NORTHWEST BREEZES WITH
OCCASIONAL NEAR GALE FORCE GUSTS WILL CONTINUE THROUGH MOST OF
TODAY. LOCALLY GUSTY CONDITIONS ARE LIKELY ACROSS THE SAN PABLO
AND SAN FRANCISCO BAYS WHERE TERRAIN PROMOTES WIND FUNNELING.
WINDS GRADUALLY EASE STARTING LATE TODAY WITH A GENTLE TO MODERATE
NORTHWESTERLY BREEZE EXPECTED EARLY TO MID WEEK. BREEZY CONDITIONS
RETURN TO THE INNER WATERS LATE WEEK AND SEAS BUILD MID TO LATE
WEEK.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 9 PM PDT THIS
EVENING FOR MRY BAY.
SMALL CRAFT ADVISORY UNTIL 3 AM PDT MONDAY FOR PT ARENA TO PT
REYES 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 9 PM PDT THIS EVENING 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 PM PDT MONDAY FOR PIGEON PT TO PT
PINOS 10-60 NM-PT ARENA TO PT REYES 10-60 NM.
SHORT TERM...MM
LONG TERM....MM
AVIATION...CANEPA
MARINE...CANEPA
VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO
FOLLOW US ON FACEBOOK, X, AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSBAYAREA
X.COM/NWSBAYAREA
WWW.YOUTUBE.COM/NWSBAYAREA
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page