Surest bet in Seattle weather: It was going to rain on Saturday
It's November 19th and it's raining in Seattle -- 0.04" to be exact as of 1 p.m.
But while weather prediction is still limited to about a 3-7 day advance period for any kind of accuracy, I probably could have told you in February it'd have likely rained today. I had about a 75 percent chance of being right.
November 19th is indeed statistically the most likely day in Seattle to have measurable rain. It's rained 91 times (well, 92 now) on this date since 1893 -- far, far and away the wettest day of the year. This chart shows how many times it's rained on any given date in Seattle since 1893:
It is a bit of a statistical quirk -- while this is indeed the wettest time of the year, November 18th (65 times) and November 20th (67 times) have had more than a 20 percent better chance of being dry than the 19th. Weird.
So those of you planning outdoor events in November, be especially wary if the 19th is a potential date. Maybe aim for a day before or after?
By the way, the driest days of the year were just about 14-15 weeks ago -- July 30th and August 4th remain tied at just 9 days of measurable rain in the past 123 years.