Shorter days, cooler temperatures coming up

The start of fall, or the autumnal equinox, occurs on the evening of Sept. 22 this year. It is around this time of the year that day and night are of nearly equal length (the exact day varies by location). In Spokane there will be 12 hours and 30 seconds of daylight on the 25th. Afterward, we head on that steady slide to shorter days and cooler temperatures.

One of the changes we’ll start to see once we are moving into the month of October, is a more active weather pattern due to the southward progression of the polar jet stream. During the summer, the polar jet spends most of its time north of the Canadian border. This fast-moving current of air (which during the winter can contain wind speeds of 200 to 300 mph) plays a part in our weather by supplying energy to the circulation of surface storms as well as directing their paths. Though the jet stream resides high in the atmosphere at altitudes of 25,000 feet above sea level and higher, it is a reflection of a strong temperature gradient at the surface. Surface fronts are situated at the leading edge of these tight temperature gradients, and the progression of these fronts often bring unsettled weather to the areas as they sweep past.