Wiki:

Earthquake weather is a type of weather popularly believed to precede earthquakes.

Since ancient times, the notion that weather can somehow foreshadow coming seismic activity has been the topic of much discussion and debate. Geologist Russell Robinson has described "earthquake weather" as one of the most common pseudoscientific methods of predicting earthquakes.

MORE: https://en.wikipedia.org/wiki/Earthquake_weather

In northern California, that usually mean ideal conditions -- not too hot, cold, humid, windy, etc.

warm day in the fall or spring... clear skies

however I do not believe there is any scientific data that backs this up

and we don't have enough major events to make any sort of statistical analysis

I didn't think there would be scientific data.

Am I wrong: It wouldn't be called a myth if it were true and backed up by facts and data ???

Down here some call overcast skies earthquake weather. Been here next to the San Andreas Fault half my life and its a myth.

Only good, positive thoughts. And tomorrow will mark the start of our recovery from the nightmare of the last four years
We've had plenty of disasters here in the North Bay in the last few years, like to get most recent cleaned up before another comes. Besides, earthquake weather is usually warm, overcast and a little windy. Today was perfectly beautiful

Having lived twice in California has not given me this opinion but I have felt that I could expect an earthquake on the 3rd day after a full moon. Not anything scientific, just a feeling.

the idea being the same a boiling hot water shattering a cold glass