Oregon weather happens in cycles

Posted: 2013-06-21

Today is the first day of summer. This doesn’t mean the same thing in Oregon as it does in my native Nebraska.

Feels like summer already

My first spring in Oregon, I couldn’t wait for “winter” to be over. I thought “gray” meant “winter” and there would come a week where “gray” just didn't happen any more, until maybe October. This is kind of how Nebraska weather works: it’s cold in the winter for roughly three continuous months, then it’s warmer and wetter in the spring for about as long and then hey presto! it’s summer for three glorious, sweaty months.

Oregon weather doesn’t work like that.

My first Oregon spring, seventeen years ago, an older friend and Oregon native explained weather here as happening in “cycles.” It’s like this:

There are two basic weather modes: GrayWet and BlueDry. They happen in succession: GrayWet follows BlueDry follows GrayWet, continously and forever. No matter what timescale you observe, GrayWet will follow BlueDry over and over again. The only things that change are the length of the cycles (are the GrayWets getting longer or shorter?) and the temperature (are the GrayWets getting colder or warmer?). (The temperature variations are almost nada, to a midwesterner. It is always spring here, temperature-wise.)

Beginning in October, the GrayWets get longer and the BlueDries get shorter. By late November you will experience a GrayWet cycle that lasts 30 days or more. But sure as day follows night, a BlueDry will happen. It might only be a day or two long — heck it might only be an afternoon — but it will happen.

But beginning in April, the GrayWets get shorter and the BlueDries get longer. This year we had about two solid weeks of BlueDry in late April/early May. This is what makes Oregon summers so tough. By the time of the Solstice, we’ve usually had at least one long BlueDry period, so transplants like me are thinking, “hey, it’s summer now, right? Just like Nebraska?” But remember the Iron Law of Oregon Weather: this cycle will end eventually. Anyway, by mid July or so, we’ll have a BlueDry cycle that lasts for a month or more.

Of course, this means that in the rapid-changey months, the cycles might be hours long.

So this is the way I’ve thought about weather for 17 years now.

“Winter” is when GrayWet periods last for weeks and BlueDry periods last for hours. Peak Winter (the longest GrayWet cycle) usually falls sometime around January.

“Summer” is when BlueDry periods last for weeks and GrayWet periods last for hours. Peak Summer (the longest BlueDry cycle) usually falls sometime around August.

“Spring” and “fall” are when GrayWet and BlueDry periods are roughly the same length (and that length might be very short indeed). Peak Spring usually falls sometime around March. Peak Fall usually falls sometime around October.