Technical NOAA Weather Discussion

FXUS66 KMTR 270703
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1203 AM PDT Wed May 27 2026

...New SHORT TERM, LONG TERM...

.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

&&

.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...
(06Z TAFS)
Issued at 959 PM PDT Tue May 26 2026

Primarily VFR conditions tonight outside of coastal areas. Guidance 
suggests some potential for MVFR CIGs to impact interior Bay Area 
airports tonight but confidence is on the lower end. High resolution 
guidance shows RH values around 80-90% in the lower levels of the 
atmosphere. This supports at least few to scattered low level clouds 
but not confident on BKN/OVC conditions. LAMP guidance shows a low 
chance for MVFR CIGs and leans towards keeping into sites VFR 
overnight. Winds are easing across the region but will remain 
locally gusty overnight. The SFO-WMC gradient will be weaker on 
Wednesday than it was on Tuesday but it will still be around -10 to -
12 mb at its afternoon peak. This supports another round of gusty 
winds tomorrow although gusts peak around 20-25 knots instead of 30-
35 knots today. Widespread showers return towards the end of this 
TAF period and continue into the rest of tomorrow night.

Vicinity of SFO...VFR through the TAF period. Not anticipating low 
clouds to develop at SFO tonight with CIGs staying above 3000 ft. 
Gusty westerly winds will diminish overnight before another round of 
breezy winds tomorrow afternoon/evening. Tomorrow's winds will be 
weaker with gusts peaking around 25 knots. Scattered showers 
approach SFO after 06Z tomorrow with shower chances increasing 
further around 12Z. 

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...MVFR CIGs continue through 17/19Z with VFR 
the rest of the day. Westerly winds are diminishing at MRY and SNS 
with winds to ease further overnight. Winds restrengthen during the 
afternoon/evening when gusts to around 20 knots are expected. 
Scattered showers are possible in the vicinity of MRY tonight with 
shower chances becoming more widespread (impacting both MRY and SNS) 
tomorrow night.

&&

.MARINE...
(Tonight through next Monday)
Issued at 916 PM PDT Tue May 26 2026

Fresh to strong northwest winds continue tonight with winds
gradually diminishing across the inner waters heading into
tomorrow. Occasional near gale to gale force gusts are possible
across the far outer waters through Wednesday afternoon. Rough
seas continue with wave heights between 12 to 16 feet through
Thursday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement until 9 AM PDT Wednesday for CAZ006-505-
     509-529-530.

PZ...Small Craft Advisory until 3 AM PDT Wednesday for Mry Bay-Pigeon 
     Pt to Pt Pinos 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm-SF Bay 
     N of Bay Bridge.

     Small Craft Advisory until 9 AM PDT Wednesday for Pt Arena to Pt 
     Reyes 0-10 nm.

     Gale Warning until 3 AM PDT Wednesday for Pt Pinos to Pt Piedras 
     Blancas 0-10 nm.

     Small Craft Advisory until 3 PM PDT Thursday for Pt Arena to Pt 
     Reyes 10-60 NM.

     Small Craft Advisory until 9 PM PDT Wednesday for Pigeon Pt to 
     Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...JM
LONG TERM....JM
AVIATION...Kennedy
MARINE...Kennedy

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Prepared by Boulder-Creek.com Weather at: Wed May 27 00:30:02 PDT 2026
From the National Weather Service