textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 753 PM PDT Sun Oct 18 2026

- Cooling trend continues through the end of the week

- Beneficial light rain showers expected mid-week

- Thunderstorms possible mid-week across southern Central Coast

UPDATE

Issued at 905 AM PDT Mon Oct 19 2026

Hot-tober straight back to June Gloom this morning. Morning satellite imagery shows widespread stratus covering the coast and inland valleys. In fact, it's a solid push of stratus with some inland peaks being covered by clouds. KOAK 12Z sounding puts the depth in the 2200-2500 foot range. Given that it's October and a lower sun angle it will take some time for clouds to erode with a 1030-1130 timeframe. No update needed this morning. Main message for today will be the cooler temps with forecast highs a few degrees below normal.

Highlights for the afternoon forecast package: We'll be fine tuning rain chances mid week. Still lots of uncertainty, specifically amounts. The real wildcard will be convection. Still several days out, but the environment could get a little spicy with convective threats/parameters.

MM

SHORT TERM

Issued at 1218 AM PDT Mon Oct 19 2026 (Today and tonight)

As the upper-level trough nears the West coast, it pushes southward until it finally settles a few hundred miles west-southwest of San Francisco by Tuesday. In the meantime, as the trough center approaches our immediate coastline, the marine layer deepens to around 2000 feet overnight accompanied with a gentle to moderate onshore flow up to 10-20 mph through Monday afternoon. Another drastic drop in temperatures due to enhanced cold air advection occurs on Monday with widespread maximum temperatures in the mid 50s to low 70s. The far interior Central Coast will remain in the 70s however. By Monday evening, winds gradually ease and become variable through Tuesday.

The upper-level trough becomes fully cut-off from the main jet stream by Tuesday. As a result, a cooler and more humid air mass gets ushered into the Central Coast and Bay Area. Ensemble Euro and GFS members continue to forecast precipitable water (PWAT) values around 0.80-0.85 inches by Tuesday evening, exceeding the 75th percentile for this time of year. To put into perspective, the most recent 00Z OAK sounding measured PWAT at 0.56 inches which falls within the seasonal norm. An increased moisture content supports the initiation of light rain (mainly offshore) while suppressing the redevelopment of the marine layer.

LONG TERM

Issued at 1218 AM PDT Mon Oct 19 2026 (Tuesday through Sunday)

Light rain showers migrate onshore Tuesday evening impacting the Central Coast first and gradually making their way through the rest of the Bay Area. As a result, the marine layer is not expected to redevelop in the next few days. The rain-producing system propagates eastward toward land on Wednesday, thereby allowing for widespread showers to persist through Thursday. The North Bay will likely see lower rainfall totals compared to the rest of the Bay Area. Given its proximity to the center of the cut-off 500 mb low, the Central Coast will likely experience the highest rainfall amounts as well as the greatest potential for thunderstorm development (<20%), particularly along the Santa Lucia Range and Sierra de Salinas. Ensemble Euro and GFS members forecast PWAT values to rise above the 90th percentile on Wednesday. According to deterministic European model, most unstable CAPE continues to trend upwards generally around 100-300 J/kg with a few spots exceeding 500-800 J/kg. The moisture and instability is available to support thunderstorm development. The alignment of these elements with orographic lift will be sufficient to result in some "wet" thunderstorms, which is why the greatest potential resides over the Central Coast higher terrain. While the winds are expected to remain light and variable through the event, any thunderstorm development can result in gusty and erratic winds. This event will be the first test to the Timber and Plaskett fire burn scars as the soil in these areas cannot absorb much moisture. If rainfall rates exceed their thresholds, the water will slip right off the surface resulting in burn scar debris flows, which may lead to flash flooding. If your home is downslope of these burn scars, now is the time to prepare for the possibility of an emergency.

By Thursday night, the cut-off low is well to our East with rainfall chances rapidly diminishing. The usual diurnal onshore wind pattern returns briefly on Friday with a persistent troughing pattern through the remainder of the forecast period, resulting in near to slightly below seasonal temperatures.

AVIATION

(18Z TAFS) Issued at 1034 AM PDT Mon Oct 19 2026

Currently MVFR-VFR. Stratus is dissipating with VFR expected by the afternoon. High clouds are streaming in from the southwest and will increase in coverage through the TAF period. Onshore winds this morning and this afternoon will back through the TAF period to become southerly. While there's no precipitation in the TAFs, there is a chance for rain showers Tuesday, especially across the coastal waters. The incoming low pressure system will deepen and mix out the marine layer, likely keeping the terminals VFR after this morning.

Vicinity of SFO...Currently MVFR with westerly flow. High confidence in VFR prevailing by this afternoon. Westerly winds will diminish and begin to back this evening, becoming southeasterly overnight and northwesterly tomorrow afternoon.

SFO Bridge Approach...After this morning, the San Mateo Bridge Approach will likely remain clear of clouds below FL070.

Monterey Bay Terminals...Currently MVFR with westerly flow at MRY and MVFR with southerly flow at SNS. High confidence in VFR prevailing by this afternoon. Westerly winds will diminish and begin to back this evening, becoming southeasterly overnight.

MARINE

(Today through Saturday) Issued at 1034 AM PDT Mon Oct 19 2026

Moderate northwesterly breezes will prevail today with hazardous conditions for small craft along the Big Sur Coast through this afternoon and Monterey Bay this afternoon through this evening. Winds will diminish and back to a gentle southerly breeze Tuesday. Moderate northerly breezes will prevail Wednesday, increasing to become fresh to strong Thursday into Friday. Moderate seas will prevail with rough seas across the outer waters Tuesday and Friday. Rain showers with a chance of thunderstorms are expected Tuesday through Thursday, especially south of Pigeon Point.

MTR WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this evening for Mry Bay.

Small Craft Advisory until 3 PM PDT this afternoon for Pt Pinos to Pt Piedras Blancas 0-10 nm.