The climate theme so far this year has been hold on and wait. After an extended spring and in some cases a record for latest in the year to hit 70/80/90 degrees across the NW, we’ve had a late season showing of summer. The Spokane NWS had a busy day Saturday noting a number of record high temperatures set for the date:
In fact, for places like Pullman, WA (95F), Lewiston, ID (100F) and Boise, ID (101F airport, 98F official), Sept 24th was the warmest autumn day on record, assuming the astronomical definition of seasons, which by the way seem to hold this year in the inland NW moreso than climatological definitions. This record setting heat was very much linked to a weather pattern that featured a broad ridge over the western half of the US and the advection of warm air ahead of the trough seen below off the west coast. Also, several places in the Palouse observed easterly surface flow Saturday which presumable providing some additional warming due to adiabatic compression coming off the N. Rockies.
After persistent troughing over the west coast, the large scale pattern changed in August, with the ridge parked over the center of the US retrograding westward and providing us with our raincheck on summer. Our tomatoes thank you, but also wait nervously for the first fall freeze.