The Tri-Cities got more rain in 22 hours than in the previous four months combined

Spring of 2022 was notoriously wet across the Pacific Northwest, but an abrupt pattern change in June left the region unusually dry through the rest of the summer and into the first half of fall. Some rain did fall during this time in the Tri-Cities, but from June 13 to October 20, only 0.39 inches of precipitation were observed.

While not unusually low for July and August (July was actually right at the climatological average), this constitutes a fairly late start to the wet season. The persistent ridging pattern over the western third of North America broke down over the last couple days, allowing for the first good soaking rain of fall for much of Washington and Oregon.

Once the rain stopped at the Tri-Cities Airport in Pasco, 0.60 inches had fallen between 11:35 Friday and 09:25 Saturday. Light to moderate rain was noted in every single five minute observation at the airport from 13:05 to 05:00 – nearly sixteen hours of straight rain.

Some stations nearby recorded even more, with nearly an inch of rain in the Hermiston area and 1.14 inches at Walla Walla. Areas to the north did not benefit quite as much. Yakima came in around a third of an inch, about a quarter inch was seen on the Hanford Site, and Moses Lake received 0.18 inches. More rain showers are possible today in some areas, especially close to the Blue Mountains and Cascades.

The pattern change also brought a significant cool down to drop temperatures much closer to average this time of year. During the first 20 days of October, most days in the Tri-Cities saw highs 10 to 15 degrees above average. On October 21, the first day fully under the influence of the new weather pattern, the high of 58° at the Tri-Cities Airport was a full five degrees below average.

Cooler temperatures in October also mean lower snow levels. While travel impacts were minor, snow was observed on some higher Cascade passes. This includes White Pass (4500 foot elevation) west of Yakima and Santiam Pass (4766 foot elevation) northwest of Bend. Higher snow totals were seen higher up.

The active pattern is forecast to continue for the foreseeable future with the next decent chance of rain in the Tri-Cities coming Monday followed by repeated chances of rain for much of next week. The Climate Prediction Center favors below average temperatures for the remainder of October with above average precipitation currently favored into mid-November. Mountain snow chances also continue through this period, with the next decent round of snow (for this time of year) coming around October 29 to November 1.