September is usually sunny and mild, with a few rainy periods that aren't too much of a nuisance.
Then, the first part of October brings cooling, but is often quite mild and not that wet.
But then something happens. The Northwest rain switch is flipped, and sometime in late October or early November we transition to our wettest, windiest weather.
The worst week of the year? Amazingly, the last week of November.
It is truly remarkable how quickly our region's weather degrades; almost like going off the proverbial weather cliff.
And folks, if the weather models are correct, it is going to happen in about a week.
But before I tell you about your sodden fate, let's look at climatology, in this case at Seattle Tacoma Airport. Here is the probability of getting .01 inch in a day. Very low during the summer, rising to about 40% in early October, but there there is the major ramp up to roughly 65% during the first week of November. From then on into March we are doomed to moisture almost every day.
But that is light rain. What about the change of getting say, .5 inches, over a week? (see below) A huge ramp up between mid-October and the first week of November to about 75%. Ouch. And we stay up there for a while.
So enjoy the last week of pleasant, mild, perfect fall weather. Take your last major hike on Saturday. The models don't think it will last, El Nino or not. During the next two week we should be making the transition to Northwest winter, first with light rain and then the heavier stuff in early November.
Our weather reckoning is coming. And the switch is about to be flipped.