Issued at 945 AM PDT Thu May 21 2026
Low clouds have mostly retreated to the coastline as of this writing. That said, the coast is expected to remain in the upper 50s to middle 60s (thanks to the marine influences) while the interior warms into the lower 80s to lower 90s under sunny skies. That said, no large scale changes are anticipated for this morning. Please see more from both the short/long term sections below.
RGass
, 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
..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.
(18z TAFS) Issued at 1107 AM PDT Thu May 21 2026
Clear skies across the interior with an expansive stratus deck along the coast. Kept HAF overcast throughout the day but a brief period of clearing is likely for MRY and SNS. Current thinking is that the marine layer will deepen to around 1000 ft tonight with a mix of IFR to MVFR stratus across the interior. LIFR and fog is expected directly along the coastline with fog potential increasing by early tomorrow morning. Clearing is expected by late tomorrow morning/early afternoon.
Vicinity of SFO, Winds strengthen to around 17 knots this afternoon/evening before easing overnight. Moderate confidence that MVFR CIGs will reach SFO around 10Z with some potential for CIGs to briefly drop below 1000 ft. It is worth noting that the HRRR shows a "donut hole" developing over SFO this morning stratus filters in through the Golden Gate Gap and fills into the East Bay/SF Bay but does not reach SFO. Confidence is slightly higher that a CIG will reach SFO overnight but it is worth noting their is some potential for conditions to remain VFR overnight.
SFO Bridge Approach, MVFR to IFR CIGs are likely to develop over the SF Bay overnight with clearing by late tomorrow morning.
Monterey Bay Terminals, CIGs have cleared from MRY and SNS with a brief period of VFR expected through 01/02Z. Given the expansive stratus deck just offshore, opted to push the arrival of stratus earlier in the TAF. Confidence increases in stratus returning around 01/02Z but it may return earlier if another eddy develops within the Bay. Generally expecting fog chances to increase early tomorrow morning, particularly at SNS but would not rule out patchy fog impacting MRY. Breezy onshore winds during the afternoon/evening will weaken overnight, becoming light to variable.
(today through Tuesday) Issued at 945 AM PDT Thu May 21 2026
Fresh to strong northerly winds continue across the far northern outer waters, resulting 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 with the occasional fresh to strong breeze possible across the far northern outer waters.
Ca, None. PZ, Small Craft Advisory until 3 AM PDT Friday for Pt Arena to Pt Reyes 10-60 NM.
