285
FXUS66 KMTR 271822
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1122 AM PDT WED MAY 27 2026
..NEW AVIATION
KEY MESSAGES
UPDATED AT 1242 PM PDT TUE MAY 26 2026
- COOLER, UNSETTLED WEATHER CONDITIONS CONTINUE TODAY AND THURSDAY
- WARMING AND DRYING TREND FRIDAY AND BEYOND
UPDATE
ISSUED AT 1005 AM PDT WED MAY 27 2026
RAIN SHOWERS PERSISTED OVERNIGHT INTO EARLY THIS MORNING WITH THE
THE SANTA CRUZ MOUNTAINS AND SANTA LUCIA RANGE PICKING UP THE
GREATEST TOTALS. AREAS OF THE SANTA CRUZ MOUNTAINS PICKED UP
GENERALLY LESS THAN 0.05" WHILE THE SANTA LUCIA RANGE SAW UPWARDS OF
0.25" AT WHITE ROCK RIDGE. THIS ACTIVITY CONTINUES TO DIMINISH LATE
THIS MORNING, BUT WE ARE EXPECTING CONVECTION TO FIRE UP IN THE EAST
BAY HILLS, EASTERN SANTA CLARA HILLS, THE SANTA CRUZ MOUNTAINS AND
THE CENTRAL COAST (COUNTY OF MONTEREY/SAN BENITO) THIS AFTERNOON.
THIS IS AS THE ATMOSPHERE BECOMES MORE UNSTABLE WITH CAPE VALUES
BETWEEN 100-400 J/KG. HOWEVER, PROBABILITIES FOR THUNDERSTORMS
REMAIN LESS THAN 10% THROUGH THE AFTERNOON AND EARLY EVENING.
ADDITIONAL RAIN SHOWERS ARE FORECAST TO INCREASE IN COVERAGE
(ESPECIALLY ACROSS THE CENTRAL COAST) LATE THIS EVENING AND INTO
THURSDAY MORNING. PLEASE SEE MORE IN THE PREVIOUS FORECAST
DISCUSSION BELOW.
RGASS
SHORT TERM
ISSUED AT 1151 PM PDT TUE MAY 26 2026
(TODAY AND TONIGHT)
THE CENTER OF THE UPPER LEVEL DISTURBANCE RESPONSIBLE FOR THE COOL
AND UNSETTLED WEATHER YESTERDAY AND TODAY WILL REMAIN MOSTLY
STATIONARY THROUGHOUT THE DAY. HOWEVER IT WILL WEAKEN SLIGHTLY OVER
THE COURSE OF THE DAY WITH SUBTLE H50 HEIGHT INCREASES FROM EARLY
THIS MORNING INTO THIS EVENING. THE UNUSUALLY COOL AIR ALOFT,
ONCE AGAIN LOOKING AT H50 LEVEL, WILL BE BELOW THE TENTH
PERCENTILE AT AROUND -21C TO -22C, WITH H85 TEMPS RIGHT AROUND THE
TENTH PERCENTILE AT 5C TO 6C. THE COOLER THAN NORMAL TEMPERATURES
ALOFT ARE TRANSFERRING TO THE SURFACE WITH LOW LYING INTERIOR
LOCATIONS RUNNING 5F-10F DEGREES BELOW NORMAL FOR THIS TIME OF
YEAR, AND MUCH COOLER THAN NORMAL AT HIGHER ELEVATIONS, ESPECIALLY
THE HIGHEST PEAKS OF BIG SUR AROUND 25F-30F DEGREES BELOW NORMAL.
AS THE UPPER LOW ROTATES OVERHEAD TODAY, PORTIONS OF THE BAY AREA,
EAST BAY AND SOUTH BAY WILL SEE PERIODS OF SUNSHINE HELPING TO
PRODUCE MARGINAL SURFACE INSTABILITY FROM AROUND 100-300 J/KG OF
CAPE THIS AFTERNOON. VERTICAL WIND PROFILES DON'T FAVOR ORGANIZED
CONVECTION, WITH LITTLE TO NO 0-6KM WIND SHEAR. LIKE YESTERDAY IN
NAPA COUNTY AND CONTRA COSTA COUNTY THE BEST CHANCES FOR RAINFALL
AMOUNTS ABOVE 0.10" WILL BE AREAS OF TERRAIN ENHANCEMENT. THE
HILLS OF EASTERN CONTRA COSTA COUNTY AND EASTERN SANTA CLARA
COUNTY HAVE APPROXIMATELY 20%-50% CHANCE OF EXCEEDING 0.10" BY
LATE THIS AFTERNOON. NBM THUNDERSTORM CHANCES ARE LESS THAN 10%
AREA WIDE.
A PORTION OF THE UPPER LEVEL LOW WILL BEGIN TO RETROGRADE BACK
TOWARD THE COAST TONIGHT INTO EARLY THURSDAY MORNING, INCREASING
RAIN CHANCES OFF SHORE THAT EVENTUALLY BEGIN TO MOVE ONSHORE ALONG
THE COAST LATE TONIGHT AND FARTHER INLAND THROUGH THURSDAY MORNING.
RAIN TOTALS ALONG THE COAST LATE TONIGHT INTO EARLY THURSDAY MORNING
WILL BE LIGHT, PRIMARILY LESS THAN A 0.10" FROM SANTA CRUZ SOUTH
DOWN THE BIG SUR COASTLINE.
LONG TERM
ISSUED AT 1151 PM PDT TUE MAY 26 2026
(THURSDAY THROUGH TUESDAY)
THURSDAY WILL CONTINUE THE UNSETTLED PATTERN WITH A SHIFT SOUTH
ACROSS PRIMARILY THE SOUTH BAY AND CENTRAL COAST AS THE UPPER LOW
BEGINS TO SHIFT INLAND TO THE SOUTHEAST DURING THE DAY THURSDAY. THE
CLOUDS AND COOLER TEMPERATURES WILL LINGER DURING THE DAY THURSDAY
WITH ONLY LIGHT RAINFALL AMOUNTS WHERE RAIN DOES OCCUR, WITH LESS
THAN A 0.10" EXPECTED.
PROGRESSIVE UPPER RIDGING BEHIND THE EXITING LOW TO THE EAST ON
FRIDAY GIVES WAY TO ZONAL FLOW ALOFT ON SATURDAY AS TEMPERATURES
BEGIN TO REBOUND BACK CLOSER TO NORMAL BY SUNDAY INTO THE BEGINNING
OF NEXT WEEK. WHILE WE DO GRADUALLY WARM UP THROUGH THE REMAINDER OF
THE EXTENDED FORECAST BEGINNING FRIDAY, A SIGNAL FOR TROUGHING IN
THE SYNTOPIC PATTERN CONTINUES BEYOND THE CURRENT EXTENDED
FORECAST THAT SHOULD HELP MAINTAIN MORE SEASONAL TEMPERATURES.
AVIATION
(18Z TAFS)
ISSUED AT 1122 AM PDT WED MAY 27 2026
THE COLD CORE 500 MB LOW CONTINUES TO STRADDLE THE CA/NV BORDER.
A SPOKE OF 700 MB TO 500 MB TROUGHING/INSTABILITY EXTENDING OUTWARD
FROM THE LOW CENTER CONTINUES TO MOVE SOUTHWARD OVER THE SOUTHERN
HALF OF OUR FORECAST AREA AT THE MOMENT. IT'S COLD FOR LATE MAY AT
THE MANDATORY PRESSURE LEVELS 925 MB THROUGH 500 MB ON THIS MORNING'S
12Z OAKLAND UPPER AIR SOUNDING: < 10TH PERCENTILE FOR LATE MAY. WITH
SOLAR INPUT AND SURFACE HEATING TODAY, EXPECT A FEW MORE SHOWERS
ALONG WITH ISOLATED LIGHTNING IN THE UNSTABLE AIR. KMUX SHOWS A RECENT
ISOLATED THUNDERSTORM OVER NORTHEASTERN SANTA CLARA COUNTY, DRIFTING
TO THE SOUTHWEST. WILL CONTINUE TO CLOSELY MONITOR KMUX RADAR AND
SATELLITE THROUGH TODAY.
THE AFOREMENTIONED 500 MB LOW AND HIGH PRECIPITABLE WATER IT HAS
ENTRAINED (NEAR 90TH PERCENTILE) BRING THE POTENTIAL FOR MORE WET
WEATHER TONIGHT AND THURSDAY. WILL CLOSELY MONITOR RADAR AND
SATELLITE IMAGERY.
VICINITY OF SFO...VFR. EAST TO NORTHEAST WIND 5 KNOTS SHIFTS TO
WESTERLY AND INCREASES TO 15 TO 22 KNOTS IN THE AFTERNOON WITH
GUSTS DIMINISHING BELOW 20 KNOTS BEGINNING 03Z THIS EVENING. WIND
SHIFTS TO SOUTHEASTERLY 5 KNOTS THURSDAY MORNING THEN TO WESTERLY
12 KNOTS THURSDAY AFTERNOON.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...LINGERING MVFR CEILINGS ARE EXPECTED TO
SCATTER OUT BY THE AFTERNOON, IF THEY HAVE NOT ALREADY. ONSHORE
MODERATE BREEZES (~10-14KT) WILL PERSIST THROUGH THE AFTERNOON WITH
THE SALINAS VALLEY EXPERIENCING GUSTS UP TO 20KTS. MVFR CEILINGS
WILL RETURN THIS EVENING (00-02Z). LIGHT RAIN SHOWERS BEGIN TO
APPROACH THE MONTEREY BAY COASTLINE LATE WEDNESDAY NIGHT WITH WINDS
SLIGHTLY DIMINISHING. MEDIUM CONFIDENCE IN THE TIMING OF THE RAIN
SHOWERS AS THEY MAY ARRIVE AN HOUR EARLIER OR LATER, THOUGH THEY ARE
EXPECTED TO STICK AROUND FOR THE REMAINDER OF THE TAF PERIOD. WINDS
BEGIN TO SHIFT SE EARLY THURSDAY MORNING. THERE IS LOW CONFIDENCE AT
THIS TIME THAT VISIBILITY WILL BE IMPACTED, HOWEVER I WOULDN'T BE
SURPRISED IF THE RAIN SHOWERS CAUSE A SLIGHT REDUCTION TO VISIBILITY
(MINIMUM 5SM).
MARINE
(TODAY THROUGH MONDAY)
ISSUED AT 1005 AM PDT WED MAY 27 2026
NORTHWESTERLY WINDS CONTINUE TO DIMINISH THROUGH TODAY AND
OVERNIGHT INTO WIDESPREAD GENTLE TO MODERATE BREEZES OVER THE
OUTER AND INNER WATERS. WIND GUSTS ALSO BECOME MORE MODERATE, WITH
THE OUTER NORTHERN WATERS EXPERIENCING LOCALLY STRONG GUSTS
THROUGH THURSDAY MORNING. ROUGH SEAS WITH HEIGHTS OF 11-16 FT
CONTINUE TO ABATE THROUGH TODAY AND BECOME MORE MODERATE (5-9 FT)
BY FRIDAY MORNING. ANOTHER ROUND OF STRONG TO NEAR-GALE FORCE
WINDS ARE EXPECTED TO DEVELOP OVER THE WEEKEND WITH BUILDING ROUGH
SEAS AGAIN.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 3 PM PDT THURSDAY FOR PT ARENA TO PT
REYES 10-60 NM.
SMALL CRAFT ADVISORY UNTIL 9 AM PDT THURSDAY FOR PIGEON PT TO PT
PINOS 10-60 NM.
SHORT TERM...JM
LONG TERM....JM
AVIATION...CANEPA/NAVARRETE
MARINE...NAVARRETE/CANEPA
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