Weathercatch: Plenty of shining during harvest moon, fall equinox

The fall equinox arrived Wednesday, signaling the astronomical farewell to summer 2021. Just two days earlier, a full harvest moon with an orange hue was visible over the Inland Northwest.

If there’s ever a time for autumnal bliss, it’s now.

Following cool weather and much-needed rainfall last weekend, the pattern flipped on Tuesday with lots of sunshine and warming temperatures. Highs this week in the Spokane area have run mostly in the low 70s. And this weekend, they’re expected to climb into the upper 70s. What’s more, overnight lows in the mid-to-upper 40s pose no threat to late-blooming petunias and the season’s last tomatoes clinging to vines.

Now that we’ve reached the autumnal equinox, the biggest and most immediate change we’ll see is less daylight at the fastest pace of the year. Days are getting shorter by 3 minutes, 24 seconds each day in our region. Compare that with early August, when we experienced a daily loss of 2 minutes, 25 seconds.

Big weather changes typically lag behind the shortening days. Although the average high temperature in Spokane is a comfortable 70 degrees this time of year, last year it climbed to almost 80 on Sept. 22. And talk about an extension to the growing season – on Sept. 23, 1966, the high temperature soared to 93 degrees, making that date Spokane’s warmest equinox ever recorded. (The autumnal equinox usually occurs on Sept. 22 or Sept. 23.)

Mid-to-late September weather tends to be more transitional, while hardcore fall usually takes hold in sometime in October. It’s akin to a ball slowly rolling down a gentle slope. For now, it’s taking its sweet time. Then, when the ball encounters the steep part of the slope in October, it dramatically speeds up. Weatherwise, that means conditions usually run relatively mild this time of year, with sizable temperature dips and widespread frost gaining the upper hand as we move deeper into October.

This week’s spectacular harvest moon, followed by Wednesday’s fall equinox says it all – summer 2021 is behind us. As the days continue to shorten, trees and plants are in the final stretch of their seasonal growth cycle. Thanks to an upper-level ridge that built up over the Pacific Northwest, they’ll enjoy a good dose of pristine weather this weekend. The sun will be out, but temperatures won’t approach the intensely hot and sometimes dangerous values we saw during summer. Highs should top out near 80 degrees and overnight lows should hover close to 50.