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