FXUS66 KMTR 281744
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1044 AM PDT Tue Jul 28 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1129 PM PDT Mon Jul 27 2026
- Breezy onshore winds expected each afternoon and evening through
early midweek
- Gradual warming starting midweek, with Moderate HeatRisk for
interior locations through the weekend
- Elevated fire weather threat across the interior North and East
Bay, Diablo and Santa Lucia Ranges this week
- Hazardous beach conditions at the Pacific Coast with an
increased risk for sneaker waves and rip currents through the
end of the week
&&
.UPDATE...
Issued at 930 AM PDT Tue Jul 28 2026
Water vapor imagery shows a relatively deep trough of low
pressure situated along the West Coast this morning, with a couple
of embedded short waves within this trough. The multiple water
vapor channels also show very dry air situated over California
this morning at the various levels. As a result, there is no
cloud cover over the state, with the exception of the marine layer
along the immediate coast. The 12z KOAK sounding shows that the
marine layer is approximately 1700 feet deep, with an impressive
inversion of nearly 12 deg above the marine layer. This warmer
layer could be seen in some of the thermal belted areas, where
overnight low temperatures stayed in the mid 60s to lower 70s,
such as Highlands Peak. Meanwhile, the drier air over the region
allow for some decent radiative cooling last night away from the
coast, with most locations staring off in the upper 40s to 50s.
The marine layer helped moderate some of the coastal locations, so
temperatures were more in the mid 50s to lower 60s.
At this time, temperatures are running similar to this time
yesterday, and expect this trend to continue through the day.
Gusty onshore winds will also develop through the day, and this
will help continue to moderate temperatures along the coast,
while inland areas will still be seasonally warm. Current forecast
looks on track, with no updates are planned for the forecast at
this time. Palmer
&&
.SHORT TERM...
Issued at 1221 AM PDT Tue Jul 28 2026
(Today and tonight)
If you read the evening AFD update micro-climates were
highlighted. Seems fitting to kick off this AFD with another
micro-climate highlight. If one looks at the overnight satellite
imagery they'll notice only patchy stratus developing. I do
expect more by morning, but patchy for now. So why is it patchy,
pockets of offshore flow most notably over the N Bay and along the
Big Sur coast. Offshore flow is a drying and warming wind for our
region. Taking a closer look at Big Sur there are two sensors
called Highlands Peak. It's close to midnight and both are
reporting temperatures near 80 degrees. N to NE flow leads to
compressional warming as the air descends the Santa Lucias, hence
the warm temperatures.
Tuesday will be another pleasant day weather wise most areas. The
longwave pattern continues to advertise broad upper level
troughing just offshore and upper level ridging to the SE.
Similar to Monday we'll see a large spread of temps from the
coast to the interior. Onshore flow will keep coast/bays in check
with highs in the 60s/70s. Farther inland with marine layer
influence will see much warmer temperatures with highs in the
upper 80s to near 100.
Given the temperature contrast expect another round of breezy
afternoon winds in the valleys and inland gaps/passes.
Tuesday night the upper level trough begins to ease with upper
level ridging building in from the east. As such, a more stable
marine layer will develop with slightly better stratus coverage.
Above the marine layer temperatures will be on the milder side.
&&
.LONG TERM...
Issued at 1221 AM PDT Tue Jul 28 2026
(Wednesday through Monday)
Wednesday will be a transition day as the longwave pattern shifts
from nearby trough to a building ridge. It should be noted the
building ridge from the east brought very dangerous heat to the
Desert SW. Not expecting that here, but a marked warm up
nonetheless. Expect an initial jump in temps of 3-5 degrees from
Tuesday to Wednesday. Still seeing some night/morning marine
stratus given lingering onshore flow. Additionally, we will
continue to see the large temp spread from the coast to the
interior.
Thursday through Monday - The heat dial gets turned up each day
and peaks over the weekend before moderating early next week. The
very warm upper level ridge to the east will overspread the region
for much of the long term. Projected 850mb temps will be in the
mid to upper 20s, which when fully mixed will easily support temps
in the 105-110 range. However, onshore flow remains at the
surface. Therefore, the fullest potential of the airmass will only
be realized across the interior. That's the key to keeping the
coastal areas and bays in check temp-wise - onshore flow. Some
guidance does show periods of easing onshore flow and that has
bust potential written all over it with coastal areas ending up
warmer than forecast. Confidence isn't high enough to fully buy
that solution just yet. Much higher confidence exists for
interior locations to experience triple digit heat. Given the
very mild airmass thermal belts will be very active too with
minor relief in the hills overnight. Could easily see temps
staying in the upper 60s to mid 70s in the hills. Therefore, as
daytime temperatures increase and less nighttime relief is
observed overall HeatRisk increases. While most areas without any
marine influence will be moderate HeatRisk from Thursday through
early next week there will be pockets of Major to Extreme for
interior Monterey/San Benito. As the weekend forecast becomes more
clear will need to take a look to see if a heat advisory is
needed.
Longer range guidance diverges on extent of the heat, but some
guidance keep the heat going for much of next week.
&&
.AVIATION...
(18Z TAFS)
Issued at 1042 AM PDT Tue Jul 28 2026
VFR is imminent for the Bay Area terminals with KHAF potentially
bouncing back and forth through the TAF period at MVFR/IFR. A local
circulation will maintain MVFR/IFR ceilings at KMRY through at least
19z with clearing expected by 20z. The relatively unorganized marine
layer continues to be a challenge to predict extent and timing.
North Bay terminals if they see stratus ceilings it may not be until
around sunrise Wednesday.
Vicinity of SFO...As mentioned above, stratus clearing is imminent with
VFR persisting through at least sunset. Hi-res guidance suggests
the potential for stratus spilling over and through the San Bruno
gap to KSFO as early as sunset with more confidence in development
after midnight, with earlier clearing time as warmer temperatures
begin to mix down by Wednesday morning.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Satellite trends indicate a local
circulation maintaining MVFR/IFR ceilings as late as 20z at KMRY
with KSNS at VFR and will continue through the remainder of the
afternoon and early evening. IFR/LIFR ceilings are possible late
in the TAF period.
&&
.MARINE...
(Today through Sunday)
Issued at 1042 AM PDT Tue Jul 28 2026
Northwest breezes will continue to be fresh to strong through the
remainder of the week into the weekend. Coastal jet regions along
the Big Sur and Point Reyes will likely see gale force gusts with
moderate seas becoming rough through the middle of the week as
northwest winds increase. Tropical activity will continue to
produce long period swell along our coastal waters into the
weekend.
&&
.FIRE WEATHER...
Issued at 152 PM PDT Mon Jul 27 2026
The elevated fire weather threat will persist across portions of
the area through mid-week. Overnight RH recovery will remain
moderate at locations at or above 2,000 feet with values around 40
to 50 percent. This will be particularly true across the
Mayacamas, highest peaks of the East Bay Hills, the Diablo Range,
Santa Cruz Mountains, Santa Lucia and Gabilan Ranges. Nocturnal
drying (rapid decrease in RH through the pre-dawn hours) may also
transpire which will increase the burn period or time in which
fire behavior may remain active. Afternoon RH will remain
critically dry with values between 20 and 40 percent, with far
southern portions of the interior Central Coast potentially seeing
min RH near 10 percent. Energy Release Components (ERC) are
projected to climb above the 95th percentile across the interior
Central Coast. Individuals across the area are advised to avoid
activities that may spark a fire. Fire crews are urged to exercise
extra caution when executing any prescribed burns, especially
where fuels, topography, and weather align.
&&
.BEACHES...
Issued at 145 PM PDT Sun Jul 26 2026
Distant tropical cyclones in the Eastern Pacific will continue to
generate 16-18 second (long-period) southwesterly swell which has
reached the coastline of the San Francisco Bay Area and Central
Coast. As such, sneaker waves and strong rip currents are the
primary concerns. Breaking waves can reach up to 12 feet along
some south and southwest facing beaches and break points, such as
Santa Cruz, Pacifica, and parts of Stinson or Ocean Beach. This
can be particularly surprising when wave heights increase suddenly
after a period of seemingly tranquil wave action. In fact,
sneaker waves can have 20+ minutes in between the larger sets
(breaking waves) with significant "flat/calm looking" times
between them. Due to the long period, sneaker waves are powerful
and can catch beachgoers by surprise, resulting in people and pets
being swept into the cold, turbulent ocean. Rip currents are
strong enough to pull even the strongest swimmers away from shore.
Check marine conditions before you head out! Swim near a
lifeguard, if possible. Maintain a safe distance from the water,
and stay away from jetties, piers, beachside rocks, and other
waterside infrastructure. Never turn your back to the ocean and if
you have small children or pets at the beach, please keep an eye
on them. Hazardous beach conditions are anticipated to persist
through Saturday afternoon.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Saturday afternoon for CAZ006-
505-509-529-530.
PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
evening for Mry Bay-SF Bay N of Bay Bridge.
Small Craft Advisory until 3 PM PDT Thursday for Pigeon Pt to Pt
Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt
Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to
Pigeon Pt 0-10 nm.
Gale Warning until 3 PM PDT Wednesday for Pt Pinos to Pt Piedras
Blancas 0-10 nm.
&&
$$
SHORT TERM...MM
LONG TERM....MM
AVIATION...JM
MARINE...JM
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Prepared by Boulder-Creek.com Weather at: Tue Jul 28 12:30:03 PDT 2026
From the National Weather Service
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