Davis receives nearly 20 inches of rain annually, which is a quite a bit compared to many cities throughout the state, but not that much from a national perspective.
Local soils can only absorb 1/2" to 1" of rainfall before water starts to run off. Runoff will puddle or run into storm drains. If the drains are blocked with leaves, water will back up onto surface streets. Soil along county roads becomes saturated after just a few inches of rain. Your car will very likely get stuck in the mud if you pull off onto a dirt shoulder.
Not all puddles are the result of rain, some are year round.
(* A ton of rain is approximately equal to one inch of rainfall on 400 square feet.)
Significant rainfall episodes, and otherwise, in Davis: January 3 - 10, 1995: 6.75" of rain. January 1 - 31, 2007: no measurable rainfall.
Average monthly rainfall: October: 1.1" November: 2.7" December: 2.5" January: 3.7" February: 2.9" March: 2.6" April: 1.2" May: .27" June - September: negligible.
December 11-12, 2014: Medium sized storm dropped 1.19 inches of rain over Davis. (Storm was overly-hyped by the news media as a potentially devestating storm for California, but ended up being kind of a normal storm for Tinytown). Late November/Early December 2014 Rain came (in spades) starting during Black Friday (November 28) 2014. Rain levels are now at normal (at least in the Bay Area) for this year. February 25-March 04 2014: Two large storm systems passed through Davis, dropping a total of 1.90 inches of rain. The first system peaked on Wednesday, Feb 26th, dropping approximately 0.42 inches of rain, and the second system peaked on Friday, Feb 28th with 1.14 inches. Miscellaneous showers contributed to the remaining precipitation. February 6-9 2014: A series of storms brought in 1.78 inches of rain. November 19, 2013: November 19, 2013was the first rain of the 2013-2014 wet season. The storm was relatively minor, dropping 0.03 inches of rain.
Also see: Thunderstorms