A rare, damage-causing tornado made landfall Saturday afternoon in a town south of the Bay Area that had not even been under a tornado warning hours earlier, as San Francisco had been. Weather experts say that it is proof of the dangers of any severe thunderstorm warning, and it could portend more chaotic, unexpected events in a warming climate.

Saturday's tornado took shape for only about five minutes, and moved in a path only 30 yards wide in the commercial district of Scotts Valley, in the Santa Cruz Mountains. It happened amid a storm cell that had shown waterspout potential over the ocean, but the area was still only under a severe thunderstorm warning, not a tornado warning.

Just before 6 am that day, San Franciscans were awakened by a blaring alarm and a text from the National Weather Service, issuing a tornado warning — the first ever issued for the city. High, intense winds still arrived within minutes, likely reaching 80 miles per hour, and causing significant damage through the Sunset, Golden Gate Park, and the Outer Richmond, and in parts of the Mission and Glen Park, where winds perhaps accelerated down from Twin Peaks.

As the Chronicle reports, the National Weather Service concluded that the damage was "consistent with straight-line winds up to 80 mph," and not tornadic winds.

Why, though, some seven hours later, did a tornado suddenly take shape 70 miles south of the city without warning?

"This is sort of a class of what we call kind of miniature supercells," says Lamont Bain, science operations officer for the National Weather Service, speaking to the Chronicle. "They have a lot of the characteristics of the storms that you see in like Kansas and Oklahoma and Texas. However, they’re on a much smaller scale."

Because of that small scale, says UCLA climate scientist Daniel Swain, tornadoes can be especially hard to simulate with existing weather models. And while radars had indicated wind shear on the ocean and a drop in atmospheric pressure that morning, Santa Cruz County remained just under a severe thunderstorm warning — and people were out and about in Scotts Valley unaware that a tornado could arrive at any second.

The one that did caused injuries when it flipped a couple of cars with people in them, and it could have done even worse.

"I think the take-home message here is that a severe thunderstorm warning still indicates that there is a threat to life and property," Bain tells the Chronicle. "You need to seek shelter when you find yourself underneath one of these alerts." Bain added that the weather service is still investigating why it failed to issue a more severe warning.

The jury is still out about whether an event like this is driven by climate change — Santa Cruz County did see similar-strength (EF1) tornadoes twice in the last 50 years, once in 1965 and one in 1986. But Swain tells the Chronicle that yes, sure, anything could be possible in a changing climate and we should brace for things like this to become more common.

It is all a big "maybe," Swain says, but, "what we do know is that the amount of atmospheric instability overall should strongly increase" as the climate warms.

As for the earthquake and tsunami warning San Franciscans received just nine days earlier, that was just an unsettling coincidence.

Previously: Surprise Tornado Touches Down In Scotts Valley