Noticed this pattern myself and it's not unique to California. I've been cross-referencing satellite imagery archives with major flood events across the UK and North America for about three years now and there does seem to be a correlation with unusual persistent contrail activity in the 48-72 hour window before significant precipitation events. Whether that's causation or just observers becoming more alert to atmospheric conditions when weather is already primed for change, I genuinely can't say.
The problem with this whole area of research is confirmation bias is absolutely rampant. People photograph trails on clear days too, they just dont post them. Before anyone goes full HAARP on this thread I'd want to see a proper control dataset - how many heavy trail days had no subsequent extreme weather? That number matters a lot.
What specifically were you observing over California? Flight path deviation from normal corridors, unusual dispersion rates, or just volume? That distinction changes the analysis considerably.