Autumn has Arrived

Thanks to a much-needed period of cooler and wetter than normal weather this past month, the hellishly hazy skies and suffocating heat of summer 2018 are now a distant memory. But while we welcomed the crisp mornings and occasional afternoon downpours that September brought, the arrival of autumn on the 22nd was a sober reminder that our days will be shorter than our nights for the next six months. We will have shaved an hour and 42 minutes of day length by the time next month’s Leschi News comes out, and after Daylight Savings Time ends on the first Sunday of November, the sun won’t set after 5 PM until January 26. Hey, at least we’re all in this together.

As a lifelong weather geek, I’ve always been fascinated by how quickly our weather worsens in the autumn, particularly compared to how slow it improves in the spring. In my experience, it’s the first week of November when the weather suddenly switches from cool and crisp to wet and windy, and we only have to get halfway through the month until the potential for major arctic outbreaks and lowland snow arises. Take November 2010 as an example: I clearly remember playing Frisbee at Garfield High School on the 3rd under bluebird skies and a record high of 74 degrees, but three weeks later on the 24th, the low plummeted to a record 14 degrees after 2–3 inches of snow blanketed the city at rush hour on the 22nd It tickles me to think that we are just a month and a half away here in Seattle from the beginning of our lowland snow chances, and we are only a few weeks away from such potential up in the Northern Interior, which saw accumulating snow to kick off November last year.

The reason why we experience such a dramatic shift in our climate in late autumn is because the north-south temperature gradient increases substantially, with dramatic cooling near and over the poles while the tropics and subtropics remain relatively unchanged. This causes the “jet stream”—the current of high-altitude winds that determines the strength and track of our storms, to suddenly become much larger and stronger. The Pacific Northwest can rapidly transition from tranquil leaf-raking weather to downright stormy conditions when this jet stream decides to take aim at the Pacific Northwest, particularly if it picks up some tropical moisture from the Western Pacific in the process.

Seattle is painfully slow to warm in the spring for two main reasons. First, snow and ice over northern latitudes reflect incoming radiation back out to space and slow warming, and second, we in the Pacific Northwest often see cool, onshore flow persisting through June before we finally break out into our gorgeous summertime pattern. While springtime heat waves do happen, they aren’t too common and are hardly as memorable as a big windstorm, flood or Seattle snowstorm.

In the meantime, enjoy your October! This will likely be the warmest month until May 2019, so be sure to get outside and make the most of it!

Charlie Phillips, a Madrona resident, received his B.S. in atmospheric sciences from the University of Washington and works in Portland as a meteorologist forecasting wind energy along the Columbia River Gorge. Check out his weather website at: charlie.weathertogether.net