FXUS66 KMTR 281606
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
906 AM PDT Thu May 28 2026
...New UPDATE, MARINE...
.KEY MESSAGES...
Updated at 1151 PM PDT Wed May 27 2026
- Cool, unsettled weather continues today
- Slight chance of isolated strong thunderstorms from mid-morning
through mid-afternoon for southern South Bay and Central Coast
- Warming and drying trend Friday and beyond
&&
.UPDATE...
Issued at 905 AM PDT Thu May 28 2026
Widespread light to moderate rain impacted the region overnight with
amounts ranging from a few hundredths of an inch up to 0.75" within
isolated heavier rain showers. Clearing is begging to occur across
Napa and Sonoma counties at this time, indicating the drying trend
across that region. Further to the south, light to moderate rain
showers continue across San Francisco and the East Bay southward. By
late morning and into the afternoon, there is a 10%-20% chance for
thunderstorms across Monterey and San Benito counties. However, if
there isn't enough surface heating to destabilize the atmosphere,
the threat for thunderstorms will diminish. In wake of the exiting
trough, conditions will begin to dry out from north to south
throughout the day. Please see the previous forecast discussion
below for additional details.
RGass
&&
.SHORT TERM...
Issued at 1151 PM PDT Wed May 27 2026
(Tonight through Friday)
A steady fetch of light rain, on the backside of the retrograding
upper level low responsible for the unsettled weather the past
couple of days, will continue over the North Bay and Bay Area much
of the overnight into early Thursday morning. A large portion of
Sonoma and Marin County (especially higher elevations) have a 50%-
60% chance of exceeding 0.25" rainfall or more by sunrise.
Relatively weak cyclogenesis will generate a surface low, just
offshore of Marin County and San Francisco County, late in the
overnight hours. As the upper level disturbance begins its shift
into the interior, the accompanying surface low will hug the
coastline for the remainder of the day. After sunrise the coastal
ranges of Santa Cruz south through the Santa Lucias along the Big
Sur coast will receive the most rainfall with efficient orographic
lift. Santa Cruz mountains have ~20% chance of exceeding 1.00" of
rain during the day, and ~75% chance of exceeding 0.50" of rain.
From the Monterey Peninsula south through the Big Sure, looking
at ~80% or higher chance of 0.50". The highest spots of the Santa
Lucias along the Big Sur have ~50% chance of 1.00" or more.
Flooding concerns are minimal given mean rainfall rates of
0.10"-0.20"/hr.
As the upper low begins a more eastward shift inland from mid
morning into the afternoon, chances for thunderstorms over the
interior begin to increase. Coverage of showers and isolated
thunderstorms have over performed somewhat, especially yesterday.
HiRes CAMs have steadily shown 100-200 (some spots slightly
higher) J/Kg of CAPE from the South Bay and the remainder of the
interior Central Coast from late morning into mid-afternoon today.
That has been enough to sustain convective showers (with periods
of moderate rainfall) with isolated thunderstorms Tuesday and
Wednesday. A limiting factor the past couple of days has been a
lack of wind shear and only pockets of weak divergence aloft. That
will change this morning and continue through the afternoon with
~25-30kts of 0-6km at any given time (sometimes more) from 8am
PDT through mid-afternoon and a larger swath of divergence aloft
near the base of the exiting closed low aloft. Along with
potential terrain influences, there will be surface convergence
into the surface low riding the coastline and some slightly backed
H85 flow at times. Overall, this is to say a brief low-top
supercell can't be ruled out from Santa Cruz County-southern Santa
Clara county around mid- morning and farther south into the
Central Coast for the remainder of the morning into the afternoon
hours. By late afternoon the potential for strong storms drops off
quickly with only lingering light rain expected in the North Bay
and southern Monterey County through the evening hours.
&&
.LONG TERM...
Issued at 1151 PM PDT Wed May 27 2026
(Friday night through next Wednesday)
Not much change in the extended forecast with some uncertainty in
the finer details of the overall synoptic pattern, but we do know
that we will begin to dry out and temperatures will begin to warm
closer to seasonal averages through the weekend and slightly
above normal for the the first half of next week at least. The
pattern is relatively progressive and does not indicate any
impactful extreme heat in our area through the extended forecast.
&&
.AVIATION...
(12Z TAFS)
Issued at 427 AM PDT Thu May 28 2026
Generally MVFR or low end VFR throughout the region, with patches of
IFR along the coast, as steady rain blankets the North Bay and comes
into the Bay Area. Through the rest of the day, the offshore low
pressure system associated with the rainfall will travel southwards
parallel to the coast, bringing the rain into the rest of the Bay
Area and the Central Coast. Lower visibilities are possible if a
shower comes over a terminal. A slight chance (10-20% probability)
of thunderstorms is possible later this morning into the afternoon
across the Central Coast, but the probabilities are too low to
include in the TAFs at this time. On the backside of the rain,
expected to arrive late morning across the North bay into the late
evening across the Central Coast, MVFR to low-end VFR ceilings will
linger into the night. Confidence in the wind directions is low to
moderate, and may depend on the exact location and position of the
low, especially closer to the coast. The general trend is for some
breezy onshore flow to develop this weekend into the evening, with
the wind pattern on Friday afternoon beyond the TAF period expected
to align with northwest flow. Some high resolution models are
showing breezy southeast winds developing across the region this
morning, but this is a lower confidence forecast. Will monitor the
observed conditions through the morning.
Vicinity of SFO... Steady rain expected to continue through the
morning with MVFR to low-end VFR ceilings expected through the TAF
period. Light southerly winds will turn to a breezy west flow this
afternoon and evening, diminishing through the night before
returning Friday afternoon beyond the end of the TAF period.
SFO Bridge Approach... Similar to SFO.
Monterey Bay Terminals... Steady rain expected imminently across the
terminals through the day, with the rainfall expected to turn more
showery in the afternoon. The highest probability for thunderstorms
lies to the south of the terminals, with around a 10% probability of
thunderstorms at the terminals themselves, but can not rule out a
stray cell moving over MRY or SNS through the later morning and
afternoon hours. Strong valley winds are possible at SNS this
morning, with some high resolution models suggesting gusts as high
as 20-25 knots. Elsewhere, breezy winds develop later this morning
and last until evening, before easing overnight.
&&
.MARINE...
(Today through Tuesday)
Issued at 905 AM PDT Thu May 28 2026
A weak system moving through the region today will bring light to
moderate winds with lingering showers through the day. Moderate
to fresh northwest winds develop Friday, then strong to near gale
force northerly winds return over the weekend and continue into
next week. Rough seas persist across the outer waters while seas
abate to moderate in the inner waters. Wave heights build as winds
restrengthen with wave heights between 10 to 12 feet expected
this weekend into early next week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through late tonight for CAZ006-505-509-
529-530.
PZ...Small Craft Advisory from 3 PM Friday to 9 AM PDT Saturday for
Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.
Small Craft Advisory from 9 PM Friday to 9 AM PDT Saturday for
Pigeon Pt to Pt Pinos 10-60 NM-Pt Pinos to Pt Piedras
Blancas 0-10 nm.
Small Craft Advisory until 3 PM PDT this afternoon for Pt Arena
to Pt Reyes 10-60 NM.
&&
$$
SHORT TERM...JM
LONG TERM....JM
AVIATION...DialH
MARINE...MM
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Prepared by Boulder-Creek.com Weather at: Thu May 28 10:30:02 PDT 2026
From the National Weather Service
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