textproduct: San Francisco Bay Area

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

(18Z TAFS) Issued at 1156 AM PDT Mon Jul 13 2026

A mix of high and mid level clouds are passing over head today, thanks to the moisture tap. Radar depicts a few elevated showers throughout the region and over the coastal waters, which could lead to a brief stint of light drizzle or rain with better chances of virga due to the dry layer at 700mb and below. There is also a less than 10% chance for elevated thunderstorms; but confidence is too low to add anything for a TAF site. VRF conditions will generally prevail.

Vicinity of SFO...Mid to high based clouds and elevated showers will continue to pass over the region. Light winds have started their daily shift, and will gradually become southwesterly to onshore later this afternoon and into the evening. The seabreeze will return bringing 10-15kt winds before easing a bit overnight. Tomorrow, a similar forecast this morning is in store for Wednesday morning. The most notable change for late Wednesday morning will increasing onshore winds between 18-20Z to about 10-15kt, with gusts to 25kt starting around 21Z. Moderate to high confidence in the forecast.

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

MARINE

(Today through Saturday) Issued at 448 AM 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.