San Francisco Tornado Warning

Screen Grab from KRON4

Evidently, the difference in wind direction between the light (left-green) and heavy (left-red) intensities of the onshoring storm freaked the meteorologist(s) out? Or, just wanted to test San Francisco's tornado alert system (which didn't work) - fortunately the San Francisco "tornado alert" was quickly cancels?

Later in the day an actual tornado did occurred south of San Francisco in Scotts Valley! (see Hook Echo below).

...AI...fills in some hook echo details in about 2 seconds after prompting...

Yes, there are specific criteria for identifying a Doppler "hook echo" on radar, which is a key indicator of potential tornado formation. Here are the main criteria:

Shape: The hook echo appears as a pendant or hook-shaped feature extending from the radar echo, usually in the right-rear part of the storm relative to its motion.

Location: It is typically found in the lower portions of a supercell thunderstorm.

Rotation: The hook echo is associated with a mesocyclone, which is a rotating updraft within the storm.

Reflectivity: The hook is caused by precipitation wrapping around the back side of the updraft, often indicating strong counter-clockwise winds.

Screen Grab CBS News First Alert Weather: Hook Echo

(Scotts Valley Afternoon Hurricane) 

While the presence of a hook echo increases the likelihood of a tornado, it doesn't guarantee one. Meteorologists also look for other signatures, such as the Tornado Vortex Signature (TVS), which indicates intense concentrated rotation.