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
From the National Weather Service
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