November was the second warmest and second driest in 76 years of Boise Airport records.
During most of the month the inter mountain region was dominated by a warm upper-level ridge which kept temperatures above normal. Pacific weather systems weakened as they approached the ridge, so they brought little of any precipitation to the Treasure Valley.
Starting on the 15th, a series of deep upper-level troughs crossed the region, but the ridge always managed to rebound between them.
On the 26th an even deeper trough crossed the western U.S. On the 27th it was centered over the northern plains states, leaving Boise under northwest flow aloft between the trough and a high pressure ridge over the northeastern Pacific Ocean.
This pattern change paved the way for a winter-like weather system to drop in from the Gulf of Alaska. The storm brought Boise the first trace of snow of the season, which melted as it fell. The average date of the first trace or more of snow is November 22nd.
A weaker system from the Gulf of Alaska moved into southwest Idaho on the 30th. Like its predecessor, it brought a mix of rain and snow, but precipitation amounts in the valley amounts were light.
