textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1201 AM PDT Thu May 21 2026

- Diurnally driven winds, with onshore winds during the afternoon and early evening

- Warm and dry weather today leads to elevated fire weather concerns for the interior Bay Area and Central Coast

- Gradual cooling trend begins Friday with seasonal temperatures for the upcoming weekend

SHORT TERM

Issued at 1201 AM PDT Thu May 21 2026 (Today and tonight)

Coastal stratus lingers across the Central Coast and has filled in on the western coast of San Mateo County. A decaying Otter Eddy within Monterey Bay combined with a dry slot paralleling the Big Sur coast is making the stratus forecast somewhat uncertain with a chance that the immediate vicinity of Monterey remains clear overnight. Confidence in inland stratus development, particularly away from the immediate Bayshore or south of Salinas, is low. Stratus should generally clear back to the immediate coast in the hours after sunrise.

The large scale pattern over central California is a balance between a ridge over the northeast Pacific and edging into the Pacific Northwest and a trough lingering over the Rocky Mountains with the axis extending into southern California and Baja California. This pattern keeps the upper level winds offshore, if light, but at the surface, a thermal trough over the Central Valley keeps the winds generally onshore with coastal breezes developing across the region during the afternoon and evening.

Low temperature this morning range from the upper 40s to low 50s near the coast, lower to middle 50s in the inland valleys, and the middle 50s to lower 60s in the higher elevations. The NBM model output is slightly overshooting the high temperatures, especially in the immediate coastal areas under the marine layer influence, so I have tamped down today's coastal highs to the upper 50s to the middle 60s. These high temperatures are liable to be an underestimate of as much as 5 degrees or so if stratus clears out earlier than the current forecast, or indeed never develops at all. Away from the immediate coast, temperatures remain near to well above the seasonal average, with highs in the 70s to the lower 80s near the bays, while across the inland valleys, high temperatures range from the middle 80s to the middle 90s. The continuing hot and dry conditions will contribute to another day of elevated fire weather concerns in the interior regions, and indeed a couple of grass fires were reported across the region, one in Contra Costa County and one in San Benito County. For those living or visiting those hot and dry regions, keep the following in mind:

* Properly dispose of cigarettes and matches * Do not use a lawn mower on weeds or dry grass * Avoid using equipment that creates sparks * Make sure campfires are completely put out * Make sure no vehicle parts drag on the ground, including towing chains * Obey burn bans & only burn with a permit

LONG TERM

Issued at 1201 AM PDT Thu May 21 2026 (Friday through Wednesday)

A gradual cooling trend begins on Friday with the upper level ridge retreating westward, allowing for more zonal upper level flow across the West Coast and a gradually thickening marine layer. By Saturday, temperatures should be near the seasonal average with highs in the middle 70s to the middle 80s inland. By the early part of next week, a cold front associated with a deep upper level low is likely to sweep through the state, which would cause highs to drop into the 70s across the inland valleys. Close analysis of the ensemble model clusters reveals a small, but significant fraction of the ensemble members (around 10-20%) keeping some level of ridging over California. There is even a slight chance of light rain or drizzle associated with an incoming front, but it's a low confidence forecast at this point with around a 20-30% probability of seeing any water falling out of the sky, and that is tilted towards the coastal regions where topography would tend to enhance the rainfall amounts. CPC extended guidance does show a slight lean towards precipitation totals above seasonal averages into the beginning of June, with the caveat that for the last weeks of May, just a couple hundredths of an inch will tie or exceed the daily average totals for downtown San Francisco.

AVIATION

(12Z TAFS) Issued at 436 AM PDT Thu May 21 2026

Shallow marine layer developed initially in Monterey Bay before spread up the Salinas Valley and then northward along the coastline. Given the shallow nature dense fog/mist has been reported. At this time impacts look to be confined to SNS, HAF, and at times MRY. Clouds will hug this coast today, but do expect VFR conditions at all terminals at some point this afternoon. Marine layer increase slightly in coverage tonight, but still not a big inland intrusion. Overall conf is moderate.

Vicinity of SFO...VFR. Onshore flow this afternoon. Tonight CIGs move through GG and head toward KOAK, but guidance suggest CIGs do remain north of terminal. THerefore, VFR tonight as well.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals... Low CIGs and fog at SNS, but local wind flow at MRY has led to in-out stratus pushes. VFR by this afternoon, but early return this evening.

MARINE

(Today through Tuesday) Issued at 436 AM PDT Thu May 21 2026

Persistent high pressure off the West Coast will maintain fresh to strong northerly breezes over the outer waters north of Pigeon Point. The stronger winds will result in hazardous conditions and rough seas through Thursday. Moderate northwesterly breezes and moderate seas will prevail for the rest of the waters. Conditions improve into the weekend as seas and northwesterly breezes become moderate.

MTR WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...Small Craft Advisory until 3 AM PDT Friday for Pt Arena to Pt Reyes 10-60 NM.