FXUS66 KMTR 132328
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
428 PM PDT Mon Jul 13 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 225 PM PDT Mon Jul 13 2026
- Monsoon moisture brings a 5-10% chance for thunderstorms
through Tuesday
- Moderate HeatRisk through Wednesday for most interior locations
- Breezy onshore winds Tuesday through Thursday afternoon
- Minor coastal flooding continues through Thursday morning due
to large tidal swings
&&
.SHORT TERM...
Issued at 225 PM PDT Mon Jul 13 2026
(This evening through Tuesday night)
Radar activity is picking up over the ocean and over land. As of
2PM, a handful of cells have produced lightning offshore but no
thunderstorms have been observed over land yet. High resolution
guidance from the RRFS and HRRR shows showers increasing in areal
coverage this afternoon/evening. Models show the highest MUCAPE
values (a few hundred J/kg of MUCAPE) over the Santa Lucia Range
with higher MUCAPE values over the marine environment. The K-index
(used to assess thunderstorm potential) shows values between 30 to
40 across the Central Coast which correlates to scattered to
numerous thunderstorms. Soundings for MRY show an inverted V shape
(dry microburst reminiscent), DCAPE of 811 J/kg and a mid-level
lapse rate around 7C/km. Soundings for SFO and OAK suggest fairly
consistent DCAPE values between 770-880 J/kg across the Bay Area and
Central Coast. At the same time, these soundings show minimal MUCAPE
(a measure of available instability) across the region. We've talked
quite a lot about MUCAPE over the last few days but let's take a
moment to highlight DCAPE. DCAPE, Downwards Convective Available
Potential Energy, is a measure of how much energy is available to a
descending parcel of air. A higher DCAPE value correlates to
stronger outflow winds or descending air from a thunderstorm. 800
J/kg of DCAPE is good for our region and indicates a good chance for
gusty, erratic winds with any thunderstorms that develop. Confidence
remains low overall as to if thunderstorms will develop given the
lack of a clear lifting mechanism and uncertainty about how much
instability is present. That being said, the most likely locations
to receive thunderstorms this afternoon/evening would be over the
ocean or over the Central Coast. This doesn't mean we won't see any
thunderstorms across the rest of our CWA today, it just means
confidence is slightly lower compared to the Central Coast/marine
environment. Thunderstorm potential continues tonight into tomorrow
morning high resolution guidance another round of showers moving
through during the early morning hours.
The key things to keep in mind this afternoon and evening: a low
chance of thunderstorms continues across the region today and
tomorrow with the highest likelihood over the Central Coast and
marine environment. The most likely hazards would be elevated fire
weather concerns, the potential for fire starts (if a thunderstorm
is able to develop), and the potential for gusty, erratic outflow
winds. In the last 24 hours several sites have reported a few
hundredths of an inch of rain. While most rain is expected to
evaporate before reaching the surface (virga), an additional few
hundredths of an inch may reach the ground with any storms that
develop.
While our main focus is on thunderstorms today, heat becomes more of
a factor starting Tuesday. High temperatures warm into the 90s to
low 100s across the interior with cooler temperatures along the
coast and SF Bay shoreline. Cooling overnight will be limited with
overnight lows only dropping into the mid 60s (lower elevations) and
70s (higher elevations). This will limit overnight relief from
hotter temperatures and result in more widespread Moderate HeatRisk
across the interior. A Heat Advisory has been issued for Tuesday
from 10AM-10PM for most of the interior Bay Area, the Santa Lucia
Range, and the Salinas Valley. Remember to take breaks, drink plenty
of water, and listen to your body if you are spending extended
periods of time outdoors on Tuesday. Another factor to consider is
the much more humid conditions resulting from the monsoonal moisture
surge. This can result in temperatures feeling hotter than they
actually are and may make residents more susceptible to heat related
illnesses than they otherwise would be (at the same temperature but
under a less humid regime).
&&
.LONG TERM...
Issued at 225 PM PDT Mon Jul 13 2026
(Wednesday through next Sunday)
Thunderstorm chances subside by late Tuesday but the hot weather
will linger through mid to late week. High temperatures cool across
most urban areas by a few degrees (80s to low 90s) while the higher
elevations and interior valleys remain hot (mid 90s to low 100s).
Moderate HeatRisk becomes patchier across the Bay Area while
remaining more widespread across the interior Central Coast. A
second Heat Advisory will go into effect for the Santa Lucia Range
and Southern Salinas Valley from 10AM to 10PM on Wednesday. If you
are not a fan of the heat, you are in luck. Temperatures are
forecast to cool beginning Thursday as upper level ridging
weakens/shifts eastward and a deep upper level trough enters the
PNW. Thursday high temperatures will be in the 80s to low 90s across
the interior, outside of the interior Central Coast where highs
linger in the upper 90s to low 100s. Fire weather concerns linger
through the extended forecast due to drier, windier weather expected
mid to late week across the region. Gusts between 30-45 mph are
expected across the higher elevations and favored mountain
gaps/passes Wednesday and Thursday. The SPC has highlighted a 40%
chance of critically dry and windy conditions across the far
interior Central Coast and along the border of the Bay Area/Central
Valley. Fuels are rapidly drying out given the warmer, drier weather
observed this week and would be susceptible to an increased risk of
fire starts. The highest risk will be across interior valleys and
the higher terrain where daytime humidity valleys will drop into the
10s to 20s.
Unsettled, cooler weather returns Friday into the weekend with model
guidance showing early potential for a return of
showers/thunderstorms. High temperatures cool into the 70s to 80s
across the interior and upper 50s to 60s along the coast. As the
previous forecaster noted, there are 5 potential tropical
disturbances in the eastern Pacific Ocean as of Monday. The GFS has
consistently showed (over the last few days) one of these tropical
waves moving northward, falling apart, and potentially bringing some
tropical moisture into California. If some sort of tropical wave
were to move into California, it could bring with it enough tropical
moisture to spur another potential round of thunderstorms and
elevated fire weather concerns. Confidence remains low in this
scenario as tropical meteorology can change rapidly. We are closely
monitoring the tropical setup in the eastern Pacific and the
potential for thunderstorms next weekend.
&&
.AVIATION...
(00Z TAFS)
Issued at 428 PM PDT Mon Jul 13 2026
Radar and satellite show northward moving high based showers over
the forecast area. Patchy coastal stratus and fog may develop tonight
and Tuesday morning. Overall conditions favor VFR with the highest
probability of LIFR-IFR along the immediate coastline.
Vicinity of SFO...VFR. Northwest to west wind 5 to 15 knots except
15 to 25 knots Tuesday afternoon and evening.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR except patchy stratus and fog /LIFR-
IFR/ nearby late tonight and Tuesday morning. Winds mainly from
northwest 5 to 15 knots.
&&
.MARINE...
(Tonight through next Saturday)
Issued at 421 PM PDT Mon Jul 13 2026
Moderate to fresh north-northwest winds across the northern outer
waters continue with hazardous conditions, along with moderate
northwest swell. Northerly winds over the coastal and outer waters
become fresh to strong mid to late week, with near gale force
gusts. Expect building seas in response to the increasing winds
and long period southerly swell late week into next weekend.
&&
.FIRE WEATHER...
Issued at 259 PM PDT Mon Jul 13 2026
A 10% chance of thunderstorms, likely dry, continues through
Tuesday morning. High resolution HRRR and RRFS guidance shows
another round of nocturnal thunderstorms possible tonight into
Tuesday morning. Confidence is low to moderate on this with the
12Z HRRR strongly in support whereas the 18Z HRRR places
convection to our north. If any thunderstorms are able to develop,
fire starts are likely given how dry the fuels are. Warming
temperatures will result in fuels rapidly drying this week with
ERC charts expected to exceed the 97th percentile across the Mid
Coast to Mendocino zone and get close to the 97th percentile
across the Central Coast. Fire weather concerns will remain
elevated Tuesday afternoon through Thursday due to near
critically dry conditions, gusty onshore winds, and very dry fuel
conditions. This may result in additional fire starts
particularly across the interior and higher elevations. Unsettled
weather is possible Friday into next weekend with returning
potential for dry thunderstorms and gusty, erratic winds.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 4 AM PDT Thursday for CAZ006-506-
508.
Heat Advisory from 10 AM to 10 PM PDT Tuesday for CAZ503-504-506-
510-513>517-528.
Coastal Flood Advisory until 4 AM PDT Wednesday for CAZ505-509-
529-530.
Heat Advisory from 10 AM to 10 PM PDT Wednesday for CAZ516-517.
PZ...Small Craft Advisory from 3 PM Tuesday to 3 PM PDT Wednesday for
Pt Arena to Pt Reyes 0-10 nm.
Small Craft Advisory until 3 PM PDT Wednesday for Pt Arena to Pt
Reyes 10-60 NM.
&&
$$
SHORT TERM...Kennedy
LONG TERM....Kennedy
AVIATION...Canepa
MARINE...Canepa
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Prepared by Boulder-Creek.com Weather at: Mon Jul 13 20:30:03 PDT 2026
From the National Weather Service
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