San Mateo, CA Weather

Key Messages

Updated at 141 PM PDT Wed Oct 21 2026

- Rain showers expected through Thursday afternoon

- Thunderstorms possible this afternoon into Thursday morning across north Central Coast

- A warming and drying trend expected for the upcoming weekend and into early next week

Short Term

Issued at 141 PM PDT Wed Oct 21 2026 (This evening through Thursday night)

The greatest potential for thunderstorms will be this afternoon and evening as up to 400-800 J/kg of MUCAPE (Most Unstable Convective Available Potential Energy) spreads across the north Central Coast. We've already seen lightning strikes around the Watsonville area with ongoing convection off of the coast. The most likely timing of this will be between now and 10 PM this evening before the cut-off low pressure system begins to push onshore over central/southern California and we lose the upper level instability aloft. The SPC issued a 2-4% tornado probability for the Big Sur coastline, thereby indicating increased potential for some low-topped supercells. If the offshore convection moves inland with rotation, there is the potential for a tornado.

Farther north across the Bay Area and North Bay, cannot rule out an isolated thunderstorm or two. Rainfall across this region is also expected to be much lighter with the position of the low pressure system farther to the south. Across the North Bay and Bay Area, expecting generally <0.30" with generally 0.25-0.75" across the north Central Coast, and 0.75-1.25" in the Santa Cruz Mountains and Santa Lucia Range through Thursday night. Any heavier rain shower and/or thunderstorm will likely produce brief heavy downpours adding to the rainfall amounts.

If severe weather does develop, here are some safety reminders:

* Have multiple ways to receive emergency alerts (i.e. NOAA weather radio, follow NWS Bay Area on social media, and/or ensuring your phone's emergency alert system is on) * Move to an interior room away from windows, if a waterspout makes landfall * Have an emergency action plan ready if you live downslope of wildfire burn scars * Avoid flooded roads. Turn around, don't drown!

Post frontal rain showers are forecast to linger into early Thursday afternoon with less than a 15% probability for thunderstorms continuing through the morning. By the Thursday evening, drying conditions are forecast to return to the region.

Long Term

Issued at 141 PM PDT Wed Oct 21 2026 (Friday through next Tuesday)

As the upper level through pushes farther inland, periods of moderate northerly winds are likely across the North Bay Interior Mountains. Winds across this region have the potential to be 15-25 mph with gusts up to 45 mph Friday night into Saturday morning.

A gradual warming and drying trend will persist across the region as weak high pressure builds in from the eastern Pacific. Low-lying areas along the San Francisco Bay, San Pablo Bay, and along the coast are likely to see minor coastal flooding over the weekend during peak high tides. This is likely to persist into at least the middle of the upcoming week.

Weatherwise, there is a great deal of uncertainty beyond Monday as the weak ridging begins to break down. There is the signal for additional troughing by late next week bringing cooler and unsettled weather conditions to the region.

Aviation

(00Z TAFS) Issued at 517 PM PDT Wed Oct 21 2026

Showers continue to develop and increase in areal coverage over the forecast area with isolated thunderstorms nearing the southern coastal waters and southernmost Monterey County. Conditions at the terminals are VFR with increasing showers resulting in MVFR possibly briefly IFR surface visibilities tonight and Thursday morning. Lingering showers Thursday with VFR conditions.

Vicinity of SFO...VFR with showers tonight and Thursday. Surface winds light and variable becoming westerly near 10 knots Thursday afternoon and evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR-MVFR with showers tonight and Thursday. East to southeast winds 5 to 10 knots except increasing up to 15 knots in the Salinas Valley tonight and Thursday morning. Winds shifting to westerly near 10 knots Thursday afternoon.