Data Viz Done Right

May 19, 2016

Rain Patterns at Mount Diablo: What 60 years of rain data tells us about the Northern California drought

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I’ve been getting deep into Alberto Cairo’s latest book “The Truthful Art” and was particularly fascinated by the Rain Patterns in Hong Kong visualisation created by The South China Morning Post.

Immediately I began to think back to our time living in Northern California and the historic drought conditions. I decided to use Mount Diablo as a representative weather station because it was one of the most complete and oldest in the Bay Area.

I decided to use this visualisation as inspiration for a version of my own. Some interesting patterns reveal themselves:

  • It hardly ever rains between the end of May and early October.
  • The most single-day rain total in the last 60 years was 5 inches on 21-Jan-1967.
  • Out of the 21,404 days in the data set, only 3,892 had any measureable rain (18.2%).
  • We lived in Pleasanton for 1,070 days. During that time, there were only 145 days of measurable rain (13.6%) and only 57.3 inches of rain during that time (less than 1/2 inch per day that it rained).
  • Over 60 years, there’s an average of 66 days of rain per year.
  • During our time living there, we saw an average of 50 days of rain per year.


My version was made with Tableau 10, so I can’t publish it to Tableau Public yet. You can download the workbook here and the data set I used here. The data was sourced from NOAA.

Finally, a special thanks to Data Schooler Nisa Mara for her feedback during the process.

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