FXUS66 KMTR 210702
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1202 AM PDT Thu May 21 2026

...New SHORT TERM, LONG TERM...

.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...
(06Z TAFS)
Issued at 926 PM PDT Wed May 20 2026

Currently a mixed bag of IFR-VFR at the terminals. Moderate to 
high confidence on IFR conditions at HAF, MRY, and SNS with VFR 
elsewhere tonight. Relatively lower confidence for HAF than the
Monterey Bay terminals as stratus has been wiped out north of the
Otter Eddy in Monterey Bay. If stratus does redevelop, it'll
likely be around 12Z. Diurnal winds will prevail.

Vicinity of SFO...Currently VFR with northwesterly flow. High 
confidence in VFR and diurnal winds prevailing through the TAF 
period. FEW/SCT IFR clouds will be possible on the north side of 
the terminal if stratus sneaks through the Golden Gate Gap.

SFO Bridge Approach...The San Mateo Bridge Approach has a lower 
probability of IFR conditions.

Monterey Bay Terminals...Currently VFR and calm at MRY and IFR 
with northwesterly flow at SNS. Moderate to high confidence on 
IFR conditions through the night; however, this Otter Eddy could
be a case where SNS continues to get fed IFR stratus while MRY
remains just on the periphery. VFR is expected by late morning 
with IFR stratus sticking close to the coast during the day.

&&

.MARINE...
(Tonight through next Monday)
Issued at 441 PM PDT Wed May 20 2026

Hazardous conditions for small craft will continue through
Thursday  for the northern outers due to rough seas and strong
northerly  breezes. Elsewhere, moderate northwesterly breezes and
moderate seas  will prevail. 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.

&&

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...Sarment
MARINE...Sarment

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Prepared by Boulder-Creek.com Weather at: Thu May 21 02:30:02 PDT 2026