FXUS66 KMTR 121904
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1204 PM PDT Sun Jul 12 2026
...New AVIATION...
.KEY MESSAGES...
Updated at 1230 AM PDT Sun Jul 12 2026
- Warmer and drier conditions continue through midweek with
Moderate HeatRisk returning across the region
- Coastal Flood Advisory for up to 1.7 feet of inundation above
ground level is possible in low-lying areas near shorelines and
tidal waterways
- Potential for thunderstorms and elevated fire weather concerns
continue today and tomorrow
&&
.UPDATE...
Issued at 922 AM PDT Sun Jul 12 2026
The forecast is on track this morning. Satellite and radar show
high clouds and elevated showers over the region. A few locations
have reported light rain showers, otherwise webcams have shown
more virga.
&&
.SHORT TERM...
Issued at 1230 AM PDT Sun Jul 12 2026
(Today and tonight)
Monsoonal moisture has started to make its way into the Bay Area and
Central Coast. ACARS soundings all show a distinct moistening of the
mid to upper levels of the atmosphere at MRY, SJC, SFO, and OAK.
This correlates with the influx of mid and high level clouds moving
over the region. Radar currently (as of midnight) shows a few
showers moving into the coastal waters and across the interior
Central Coast. NBM guidance does not show showers reaching the area
until late Sunday morning. This increases confidence in the high
resolution models (HRRR, NAM) that have consistently showed showers
starting Saturday night into Sunday morning before becoming more
widespread Sunday into Monday. NBM guidance shows a 5% chance of
scattered thunderstorms on Sunday with high resolution guidance
suggesting thunderstorm potential will increase starting early this
morning. The overall confidence that high based thunderstorms
(compared to high based showers) will develop today and tomorrow
remains low given a lack of forecast instability in the models. The
NAM shows the most instability across the region but keeps it
limited to a few hundred J/kg of MUCAPE. While the overall
thunderstorm risk is low, that does not mean we won't see any
thunderstorms develop today or tomorrow. It often takes just a few
hundred J/kg of MUCAPE for a thunderstorm to develop here. This is a
low probability, high impact scenario wherein if a thunderstorm
develops, fire starts will be more likely given how dry the fuels
are. Another aspect of this is how much precipitation will reach the
surface. Given the high based nature of these storms any
precipitation that falls is likely to evaporate before it reaches
the ground (virga). Models do support some light rain making it to
the ground but this peaks at a few hundredths of an inch. To sum it
up, shower activity associated with the monsoonal moisture surge
will increase over the next day and a low potential for dry
thunderstorms to develop remains on the table.
Temperatures remain in the upper 80s to low 90s across the interior
today with the far interior Central Coast peaking in the upper 90s
to low 100s. Coastal areas and the SF Bay shoreline will see
temperatures peaking in the 70s to low 80s. Conditions may feel more
humid during the day due to the influx of monsoonal moisture across
the region. Temperatures drop into the 60s across the lower
elevations Sunday night and remain in the 70s across the higher
elevations. Widespread Moderate HeatRisk is expected across the
higher elevations today with patchy Moderate HeatRisk across the
urban portions of the Bay Area.
&&
.LONG TERM...
Issued at 1230 AM PDT Sun Jul 12 2026
(Monday through Saturday)
Beyond Monday's thunderstorm chances (discussed in Short Term), shower
and thunderstorm potential will dissipate Tuesday with most
models suggesting the monsoonal moisture surge will diminish
across our CWA. ECMWF guidance suggests enough moisture may linger
during the day on Tuesday to see an isolated shower or two across
the higher terrain but confidence is low in that scenario.
Another round of monsoonal moisture, potentially bringing showers
back to the region, is possible Friday into next weekend. The
forecast remains in flux with regards to a second moisture surge
so stay up to date on the forecast this week.
Outside of shower potential, upper level ridging will continue to
dominate the western United States with the center of the high
located over the Intermountain West. Temperatures warm into the
upper 80s to 90s across the interior with low 100s possible across
the usual hotspots (far interior East Bay, interior Central Coast)
Tuesday and Wednesday. Coastal areas will stay in the 60s to 70s
with low 80s possible along the SF Bay shoreline. Widespread
Moderate HeatRisk is expected across the higher elevations and most
of the interior Bay Area. If you are spending significant periods of
time outdoors, make sure to listen to your body, take breaks in the
shade, and drink plenty of water. Cooler temperatures return
Thursday into the weekend as upper level ridging weakens and shifts
eastward while a deep upper level trough pushes into the PNW.&&
&&
.AVIATION...
(18Z TAFS)
Issued at 1203 PM PDT Sun Jul 12 2026
Monsoonal moisture will continue to surge into the region, leading
to high clouds, elevated rain showers, and VFR conditions for the
main terminals. Surrounding the sites, in the terrain, we can expect
to see bubbling cumulus and elevated convection, which could produce
brief pockets of rain and gusty winds. Should enough convective
ingredients come together, which is currently sitting at a less than
10% chance, we could get an isolated thunderstorm or two.
Vicinity of SFO...Mid to high based clouds and elevated showers will
continue to pass over the region. Light winds have started to shift
and will gradually shift o the southwest for a brief period this
afternoon. The seabreeze will return bringing 10-15kt winds before
ease a bit overnight. Some model guidance shows a subtle hint of a
shallow marine layer late tonight and into early Monday morning. A
few low clouds could flirt around the Bay, but VFR conditions should
prevail.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Light winds, high clouds, and elevated
showers will pass over the region today. A mix of light rain showers
and virga will be possible, with most locations remaining dry until
the profile moistens up. VFR conditions are expected; however,
similar to the SF Bay, there is subtle hint for stratus late tonight
and into tomorrow morning. Opted to hint at it rather than socking
terminals in.
&&
.MARINE...
(Today through Friday)
Issued at 922 AM PDT Sun Jul 12 2026
Moderate to fresh northerly winds are outer waters leading to
hazardous conditions. Otherwise, expect light to moderate north-
northwest winds with moderate northwest swell. Winds and seas
build by the middle of next week.
&&
.FIRE WEATHER...
Issued at 439 AM PDT Sun Jul 12 2026
Warm and dry conditions persist through much of the upcoming
week, especially away from the coastal marine influences which are
forecast to persist. This will increase fire weather concerns as
fuels rapidly dry out due to low humidities. Fire weather concerns
further increase later tonight into Monday as a surge of
monsoonal moisture advects northward around the western periphery
of the high pressure over the Desert Southwest and Intermountain
West. If thunderstorms are able to develop, dry lightning and
gusty, erratic outflow winds would be the main hazards. The
limiting factor is the lack of instability over our region those
days. Thus, we will continue to closely monitor these conditions
through the weekend. Given the combination of the potential for
dry lightning and rapidly drying fuels, it is important to stay up
to date on the forecast as it evolves.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 4 AM PDT Thursday for CAZ006-506-
508.
Coastal Flood Advisory until 4 AM PDT Wednesday for CAZ505-509-
529-530.
PZ...Small Craft Advisory until 3 PM PDT Wednesday for Pt Arena to Pt
Reyes 10-60 NM.
&&
$$
SHORT TERM...Kennedy
LONG TERM....Kennedy
AVIATION...KR
MARINE...KR
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Prepared by Boulder-Creek.com Weather at: Sun Jul 12 12:30:05 PDT 2026
From the National Weather Service
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