FXUS66 KMTR 031139
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
439 AM PDT Sun May 3 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1201 PM PDT Sat May 2 2026

 - Cooler temperatures through the early part of this week with a
   chance for drizzle and light rain, mainly along the coast

 - Widespread stratus persists overnight and into the morning
   through Sunday

 - Warmer and drier conditions return for the middle of the week

&&

.SHORT TERM...
Issued at 201 AM PDT Sun May 3 2026
(Today and tonight)

Onshore winds continue to carry clouds and cooler air farther 
inland. 24 hour trends show cooler to much cooler air is reaching 
the higher elevations of the forecast area as well. Temperatures 
vary from the 50s to the 40s at 1 am. A cloudy, chilly start and 
continuation of cool air advection will slow the diurnal warming 
process today. There may be spotty light drizzle. Forecast highs 
are in the 60s today though it may be difficult to break out of 
the 50s along the immediate coastline. The best chance of the sun 
breaking through the clouds will be farthest inland from late 
morning through afternoon. Onshore winds, low clouds and chilly 
temperatures prevail tonight. A few additional patches of light 
drizzle are possible.

&&

.LONG TERM...
Issued at 201 AM PDT Sun May 3 2026
(Monday through Saturday)

Residual polar jet stream winds on the back side of the 500 mb 
closed low currently to our west will have already merged with 
subtropical jet stream winds by Monday. By Monday the center of
the 500 mb low is forecast to be located over the Central Coast 
to the Sierra Nevada/westernmost NV. The forecast gets a little
more challenging later Monday and early Tuesday with respect to
wet weather potential over our forecast area. Our current official
forecast carries light rain (0.10" or less) developing over the 
North Bay and the East Bay and dry elsewhere during this time. 
However, something to keep in mind is recent output e.g. from the 
ECMWF/GFS/NAM show greater measurable rain later Monday and early 
Tuesday. Lingering cold air aloft, with the 500 mb low cold core, 
including possibly temporarily surface cooled air i.e. higher
surface pressures locked over the highly varied terrain of CA 
while the mechanism for rainfall in this case becomes warm air 
advection at ~ 850 mb to 700 mb (up to ~ 10K feet up) arrives 
from the north and interacts with the colder air. At this time 
per model forecasts it's forecast as stratiform precipitation vs
convective/unstable. Precipitable water is still forecast to peak
0.90" to 1" during this time. If the wetter pattern does develop,
it'd bring more widespread beneficial light to moderate rain across
more of our forecast area. Stay tuned to further updates.

From mid to late week high pressure aloft moves in from the west 
and northwest. Compressional warming within the high will steepen 
850 mb temperatures well above normal and likewise with the help
of the May sun angle, surface temperatures will warm well above 
normal for early May. A quick check on forecast 850 mb temps on 
the ECMWF show readings nearing the 90th percentile on Oakland 
upper air sounding climatology for the time of year. Daytime 
surface high temperatures far from any cooler maritime influences
will climb to the 80s to lower 90s by late in the week.

&&

.AVIATION...
(12Z TAFS)
Issued at 438 AM PDT Sun May 3 2026

Predominantly MVFR CIGs through late this morning/early 
afternoon. Low to moderate confidence in the second half of the 
forecast period. HREF guidance shows low clouds across the region 
for much of the day but recent guidance shows these CIGs staying 
just above 3000 ft (3500- 5000 ft). With the marine layer 
deepening and mixing out as upper level troughing dominates the 
short term forecast, it doesn't seem out of the question for 
OVC/BKN conditions to prevail but stay above that 3000 ft 
threshold. As such, went with a slightly more optimistic TAF that 
keeps OVC/BKN conditions within the VFR category. Increasing 
confidence in VFR conditions for the second part of today is that 
ceilings have been rising over the last few hours with most sites 
on the MVFR/VFR border. It will definitely need to be watched 
closely with the potential for the marine layer to win out and 
MVFR conditions to prevail for much of today/tonight. Otherwise, 
winds generally stay onshore with locally breezier afternoon and 
evening conditions expected.

Vicinity of SFO...MVFR with VFR conditions returning by late 
morning. Low to moderate confidence that CIGs will stay overcast but 
within the VFR category this afternoon/tonight. This is supported by 
GFS-MOS, GFSLAMP, and HRRR guidance with only the more pessimistic 
NAM-MOS showing MVFR conditions returning around 05/06Z. If MVFR 
conditions do return tonight they would likely last through the end 
of the TAF period but cloud cover may become more patchy towards the 
end of the period. Breezy onshore winds return during the 
afternoon/evening but did not see any major signs of stronger gusts 
returning today.

SFO Bridge Approach....Similar to SFO.

Monterey Bay Terminals...CIGs are on the MVFR/VFR threshold with 
predominantly MVFR conditions expected through late this 
morning/early afternoon. Low to moderate confidence that VFR 
conditions will return this afternoon with CIGs hanging between 3500-
5000 ft. There is some potential for MVFR CIGs to dominant the 
entire forecast period but leaned towards CIGs staying just above 
MVFR due to HRRR guidance and recent GFS-MOS and GFSLAMP guidance. 
Breezier onshore winds return during the afternoon/evening with 
gusts between 15 to 20 knots expected at SNS. 

&&

.MARINE...
(Today through Friday)
Issued at 438 AM PDT Sun May 3 2026

Winds continue to diminish and seas continue to subside through
the remainder of the morning. A gentle to moderate northwest
breeze and moderate seas are expected to prevail this afternoon
into the early work week. Winds to increase and seas to build
late week into next weekend.

&&

.BEACHES...
Issued at 438 AM PDT Sun May 3 2026

Long period northwest swell, with periods of 15 seconds or above, is 
expected to arrive along the Pacific coast today. These long period 
swells increase the risk of sneaker waves and rip currents, 
particularly as the period between swell impulses results in lulls 
of around 20 to 30 minutes before larger sets of waves arrive. Due 
to the dangers, a Beach Hazards Statement for all Pacific coast 
beaches remains in effect until 11 PM Sunday night. Never turn 
your back to the ocean! Don't be fooled by calmer seas; observe 
the waves for at least 20 minutes before approaching the coast.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through this evening for CAZ006-505-509-
     529-530.

PZ...None.
&&

$$

SHORT TERM...Canepa
LONG TERM....Canepa
AVIATION...Kennedy
MARINE...Kennedy

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Prepared by Boulder-Creek.com Weather at: Sun May 3 06:30:03 PDT 2026