When does it rain?

"It rains a lot in Washington"  Growing up in the Pacific Northwest this is something you hear often from people who do not live here or did not grow up here.  My first maintenance job on a golf course was at the age of 15.  I worked full time in the Summer at Avalon Golf Links and weekends (when possible) throughout the school year to make extra cash, I continued that job through high school each and every summer since on different golf courses, in different states and different roles.  
My brother, Jon and I drove together many of those days with the windshield wipers clearing the way, dreading the day of rain ahead, 'what are we going to do today?' in the back of my mind, always worried that the rain gear wouldn't keep me dry through the day.  More days than not the skies seemed to clear and much of the work day would be absent of precipitation.
High school golf practice started in late February.  I can only recall a hand-full of days that we got rained out and couldn't practice.  I remember a particular day that got cancelled due to lightning, but that's a different story for a different day.

In January of 2007, I returned to Washington by accepting the Assistant Superintendent job, here at Aldarra Golf Club.  That first month it rained 3.38" (I had to look it up.)  Even though I grew up in this climate it was difficult to adjustment.  Rain events (and winter) were so different in Michigan and New Jersey, high rain total days occured in a few hours of rain or complete wash outs followed by sun.  In 2019, we had 4 days that the rain total was greater than 1" (average is 5 for Seattle) compared to New York City which had 15.

Jon sent me a message one day "80% of rain in Washington occurs at night."  A player on the team, which Jon was coaching, told him that in passing, who heard it from the Professor in his meteorology class that day.

Instantly, I  thought of all those days driving to work in high school and many days since, could this possibly be true?  In 2018 we purchased a new weather station that makes collecting and reviewing this data possible.   So, finding out the answer to this question or theory has been a decade in the making.  Day is defined as the time from actual sunrise to sunset and night as the actual time from sunset to sunrise.  There is a small grey area in there as the weather station only records rainfall totals per hour.  I tried to be as accurate as possible in splitting that line.

Here is the rainfall graph for November 18th, which had the highest rain total for a single day in November of 0.41 inches.  Sunrise was at 7:18am and sunset at 4:29pm.   Through the 5pm hour, it rained 0.19" So the day total was .0.19'" (44%) and it rained 0.23" (56%) at night.

I broke down each day and compiled that data into totals for each month of 2019.  (When I find time I might do 2018.)  Below is the breakdown for the month of November.

And the totals for each month of the year

Its not quite 80% but the data does show more rain occuring at night than during the day, two to one.  One year of data doesn't prove anything or show a trend, but its definitely interesting to note the difference.  So yes, it rains a lot in Washington, 185 days of measureable rain days this, but most of it occurred when its not possible to play golf.