415
FXUS66 KMTR 011838
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1138 AM PDT FRI MAY 1 2026
..NEW AVIATION
KEY MESSAGES
UPDATED AT 223 PM PDT THU APR 30 2026
- WARMING AND DRYING TREND CONTINUES TOMORROW FOR AREAS AWAY
FROM THE COAST
- OVERNIGHT AND EARLY MORNING STRATUS REMAINS IN THE FORECAST AS
THE MARINE LAYER DEEPENS INTO THE WEEKEND
- COOLER CONDITIONS THIS WEEKEND WITH A CHANCE OF DRIZZLE AND/OR
LIGHT RAIN INTO EARLY NEXT WEEK
SHORT TERM
ISSUED AT 149 AM PDT FRI MAY 1 2026
(TODAY AND TONIGHT)
STEADY AND COOL NORTHWEST WINDS CONTINUE OVER THE COASTAL WATERS
WITH SEA SURFACE TEMPERATURES VARYING FROM 54F TO 59F (~ 2F TO 3F
ABOVE MAY NORMALS). COASTAL STRATUS CONTINUES TO DEVELOP WITH AN
INLAND INTRUSION TAKING PLACE PER SATELLITE AND SURFACE OBSERVATIONS.
A LOWER TO MID LEVEL THERMAL RIDGE IS CAPPING STRATUS CLOUDS
WHILE A CLEAR SKY ABOVE IS ALLOWING NOCTURNAL RADIATIVE COOLING.
CURRENTLY, A 500 MB HEIGHT RIDGE EXTENDS FROM THE EASTERN PACIFIC
TO NORTHERN CALIFORNIA, THE PACIFIC NORTHWEST, ALBERTA AND
SASKATCHEWAN. AIR TEMPERATURES CURRENTLY VARY FROM THE MID 40S TO
50S IN THE LOWER ELEVATIONS TO THE 60S IN THE HIGHER ELEVATIONS,
WHERE IT'S MILDER WITHIN THE LOWER LEVEL TEMPERATURE INVERSION.
STRATUS CLOUDS WILL CLEAR TO THE COASTLINE UNDER PEAK DIURNAL
MIXING LATER TODAY. DAYTIME HIGHS WILL CLIMB A FEW DEGREES ABOVE
EARLY MAY NORMALS INLAND TO NEAR NORMAL ALONG THE IMMEDIATE COAST.
HIGH TEMPERATURES WILL VARY FROM THE 60S COASTSIDE, 70S BAYSIDE
TO THE LOWER TO MID 80S FAR INLAND. TONIGHT, THE AFOREMENTIONED
500 MB RIDGE WILL SHIFT EASTWARD AND WEAKEN ALLOWING FOR COOLING
ALOFT TO COMMENCE. COASTAL STRATUS REDEVELOPMENT AND ONSHORE BREEZES
WILL POTENTIALLY USHER STRATUS FARTHER INLAND TONIGHT AND SATURDAY
MORNING.
LONG TERM
ISSUED AT 149 AM PDT FRI MAY 1 2026
(SATURDAY THROUGH THURSDAY)
AN EASTWARD MOVING 500 MB OPEN WAVE TROUGH APPROACHING THE PACIFIC
NORTHWEST WILL CLOSE OFF BY LATE TODAY. BEHIND THE 500 MB TROUGH A
SHARPENING 500 MB RIDGE WILL BECOME UNSTABLE, FURTHER SUPPORTING
THE CLOSING OFF 500 MB LOW. THIS OFTEN HAPPENS WHEN POLAR JET
STREAM WINDS ARE UNABLE TO FOLLOW SHARP 500 MB RIDGE CONTOURS,
FIRST HEADING EASTWARD THEN FLOWING BACK WESTWARD, CARVING OUT AND
CLOSING OFF A 500 MB LOW TO THE SOUTH. THIS 500 MB LOW WILL MOVE
SOUTH WHILE THE 500 MB RIDGE ALSO CLOSES OFF TO THE NORTH, FORMING
A REX BLOCK PATTERN OVER THE WEEKEND AND EARLY NEXT WEEK. DYNAMIC
COOLING ALOFT WITH LOWERING 500 MB HEIGHTS OVER OUR AREA WILL
DEEPEN THE MARINE LAYER, WITH FURTHER COOLING TAKING PLACE AND
POTENTIALLY PRODUCING PERIODIC LIGHT DRIZZLE AND/OR LIGHT RAIN.
IT'S A LOW CONFIDENCE FORECAST IN TERMS OF HOW MUCH PRECIPITATION
MAY RESULT. AT THE MOMENT IT DOES NOT LOOK LIKE VERY MUCH I.E. UP
TO A FEW HUNDREDTHS; MODEL FORECASTS ARE VARYING IN SOLUTIONS. STAY
TUNED TO UPDATES.
THE REX BLOCK IS NOT FORECAST TO LAST VERY LONG, IT'S LIKELY TO
BEGIN WEAKENING AND BREAKING DOWN BY THE MIDDLE OF NEXT WEEK. THE
SUBTROPICAL JET STREAM ATTACHES TO THE BASE OF THE CLOSED 500 MB
LOW OVER THE WEEKEND AND EARLY NEXT WEEK ASSISTING WITH EJECTING
THE LOW EASTWARD MID TO LATE NEXT WEEK. BTW, THE STRENGTH OF THE
SUBTROPICAL JET STREAM IS LIKELY IN RESPONSE TO RECENT SURFACE
WATER WARMING OVER LOWER LATITUDES. THE 500 MB LOW GETTING PICKED
UP BY THE SUBTROPICAL JET STREAM ALLOWS THE POLAR JET STREAM OVER
THE PACIFIC TO HELP MOVE THINGS ALONG TO THE EAST AS WELL, USHERING
IN A NEWLY ARRIVING 500 MB MID-LATITUDE TROUGH WITH THE POTENTIAL
FOR SHOWERY WEATHER OVER NORTHERN CALIFORNIA LATE NEXT WEEK.
AVIATION
(18Z TAFS)
ISSUED AT 1135 AM PDT FRI MAY 1 2026
STARTING OUR MAY GRAY SEASON OFF RIGHT WITH THE COASTAL STRATUS DECK
LARGELY IMPACTING OUR REGION THIS MORNING WITH MVFR CONDITIONS. MOST
SITES ARE EXPECTED TO CLEAR OUT SHORTLY AFTER 18Z TODAY IF THEY HAVE
NOT ALREADY WITH SOME LINGERING LOW-LEVEL CLOUDS. WIDESPREAD VFR
CONDITIONS ARE FORECAST BY THE EARLY AFTERNOON ACCOMPANIED BY BREEZY
WINDS AND HIGH CLOUDS. HAF IS AN EXCEPTION AS THEY WILL CONTINUE TO
EXPERIENCE IFR-MVFR CLOUD DECKS THROUGHOUT THE DAY AND NIGHT. THE
STRATUS DECK WILL RETURN TO MOST SITES ON SATURDAY BETWEEN 02-08Z
AND PERSIST UNTIL LATE SATURDAY MORNING.
VICINITY OF SFO...IFR/MVFR CIGS CURRENTLY AT THE BAY AREA TERMINALS
THIS MORNING WITH CONDITIONS FORECAST TO IMPROVE TO VFR AROUND 20Z.
WINDS INCREASE OUT OF THE WEST-NORTHWEST THIS AFTERNOON WITH GUSTS
UP TO 25 KT AT SFO. WINDS DIMINISH IN THE EVENING WITH MVFR CIGS
RETURNING BY AROUND 02Z-04Z SATURDAY WITH HIGH CONFIDENCE OF THEM
PREVAILING THROUGH EARLY SATURDAY MORNING. THERE IS A 30%-45%
PROBABILITY OF CIGS LOWERING TO IFR BETWEEN 04Z-14Z SATURDAY, YET
CONFIDENCE IS NOT HIGH ENOUGH TO INCLUDE IN THE CURRENT TAFS.
EXPECTING VFR CONDITIONS TO RETURN MID-TO-LATE MORNING ON SATURDAY
WITH ONSHORE WINDS INCREASING ONCE AGAIN.
SFO BRIDGE APPROACH...SIMILAR TO TODAY, MAY SEE AN EARLIER CLEARING
ACROSS THE APPROACH ON SATURDAY MORNING. OTHERWISE, SIMILAR TO SFO.
MONTEREY BAY TERMINALS...VFR CONDITIONS FOR SNS WILL SETTLE IN UNTIL
THIS EVENING WHEN THE STRATUS DECK BEGINS TO MOVE ONSHORE. MRY WILL
REMAIN MVFR THROUGH 20Z FRIDAY, EXPERIENCE A BRIEF CLEARING/VFR
PERIOD BEFORE TRANSITIONING BACK TO MVFR BY 01Z SATURDAY. BREEZY
WESTERLY WINDS WILL ASSIST IN THIS BRIEF CLEARING PERIOD BEFORE
CALMING DOWN BY THE EVENING. BOTH SITES WILL BE ON THE BORDER
BETWEEN MVFR-IFR AGAIN WITH MODERATE CONFIDENCE OF IFR CIGS TO
TRICKLE IN LATE TONIGHT INTO THE OVERNIGHT HOURS AND WILL REMAIN
UNTIL SATURDAY MORNING.
MARINE
(TODAY THROUGH WEDNESDAY)
ISSUED AT 451 AM PDT FRI MAY 1 2026
A FRESH TO STRONG NORTHWESTERLY BREEZE CONTINUES INTO SATURDAY
BEFORE WINDS DIMINISH, BECOMING MODERATE TO FRESH, LATE SATURDAY
INTO SUNDAY. MODERATE, WIND DRIVEN, SEAS WILL BUILD TO 10 TO 12
FEET ACROSS THE NORTHERN OUTER WATERS AND 8 TO 10 FEET ACROSS THE
REST OF THE WATERS TODAY THROUGH SATURDAY AFTERNOON. SEAS SUBSIDE
LATE SATURDAY INTO SUNDAY AS WINDS CONTINUE TO DIMINISH NEXT
WEEK.
MTR WATCHES/WARNINGS/ADVISORIES
CA...BEACH HAZARDS STATEMENT FROM SATURDAY MORNING THROUGH SUNDAY
EVENING FOR CAZ006-505-509-529-530.
PZ...SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 9 PM PDT THIS
EVENING FOR PT ARENA TO PT REYES 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 9 AM PDT SATURDAY FOR PT ARENA TO PT
REYES 10-60 NM.
SHORT TERM...CANEPA
LONG TERM....CANEPA
AVIATION...NAVARRETE/RGASS
MARINE...KENNEDY
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