FXUS66 KMTR 271706
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1006 AM PDT Wed May 27 2026

...New UPDATE, MARINE...

.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...
(12Z TAFS)
Issued at 420 AM PDT Wed May 27 2026

Patches of MVFR ceilings have developed within the East and South 
Bays, in addition to extensive MVFR-IFR cloud cover across the 
coastal regions south of the Golden Gate and into the interior 
Central Coast. This cloud cover should clear throughout the morning, 
and the rest of the region remains VFR with some scattered low 
clouds through the evening when MVFR-IFR stratus develops for the 
coastal and mountain regions. Scattered showers will be possible 
this afternoon in the higher elevations, and then turn widespread 
tonight into Thursday morning as a low splits off in the North Bay, 
retrogrades offshore, and parallels the coast. The back side of this 
shower activity is only expected to widespread shower activity is 
only expected to begin across the North Bay close to the end of the 
TAF period. Light to gentle winds should continue through the 
morning, with a strong SFO-WMC gradient supporting onshore flow in 
the afternoon and evening, although gusts will top out around 20-25 
knots at the terminals. Winds later this evening through the end of 
the TAF period may vary depending on the track and location of the 
offshore low.

Vicinity of SFO... Low confidence of an MVFR ceiling popping up at 
the terminal area this morning, but the bulk of the stratus deck 
should remain to the west of the San Bruno Gap. Breezy west winds 
will develop this afternoon and evening with gusts of 20-25 knots 
expected, before winds diminish and shift to the south and southeast 
overnight. Scattered showers will approach the terminal around 03-
06Z before more widespread activity arriving later tonight through 
Thursday morning.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... MVFR ceilings and scattered showers 
continue through the next several hours before low-end VFR 
conditions return for the day. Breezy west winds develop in the 
afternoon and evening with gusts to around 20 knots. Widespread 
showers accompanied by MVFR-IFR ceilings and a wind shift to the 
southeast are expected to approach the region late tonight into the 
early hours of Thursday morning.

&&

.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...DialH
MARINE...Canepa

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Prepared by Boulder-Creek.com Weather at: Wed May 27 10:30:03 PDT 2026