Early Season vs. Late Season California Rainfall

This blog posting edited 17:25, 16 Oct.

Grandma Ann wonders about correlation between rainfall at different times of a wet season in California. These are interesting questions that I ought to have been curious enough to answer already, but as usual I didn't see the forest (interesting questions) for the trees (rainfall data). I'm often in the position of seeing the forest at work, but not the trees, so this is a nice turnabout.

The following graphs are one a stab at an answer, knowing that there's more than one way to slice the data and therefore that my answer is likely incomplete.

Low-Low appears correlated more strongly than Low-High. I wouldn't put any money on a High-Low correlation, however.

Here's how early rainfall correlates with the remaining season of rainfall.

And here's the remaining ways one can conceive to divvy up the months

If there's correlation, it's to a low early season leading to a low subsequent rainfall and a low total. We humans just love correlation, even when it's not justified.


  1. I am so glad you did this because I wanted to, but procrastinated. I was afraid I would have to plot this data up:

    I just eyeballed it and it looked like there was no correlation. Glad you did the legwork and showed that is true.

    Grandma Ann might have said rain in March and beyond. The jet stream usually dips south over us in Feb-March. It would be interesting to see the plots up for Feb-May.

  2. Thanks, Grace. I put in a couple more graphs to capture Feb-March and beyond.

  3. Ignore the trend lines. Instead focus on an imaginary horizontal line at the median rainfall total of about 7.5".