Spring-like weather paid Boise and the rest of southeast Oregon and southwest Idaho an extended visit in February. Starting the day after Groundhog Day, temperatures were above normal most days for almost three weeks, and eleven nights had lows above freezing at Boise.
By the 5th the snow had melted down to a trace, ending 52 days of continuous snow cover of an inch or more. This was the 5th longest period on record, exceeded only during four of the infamous winters of the 1980s.
February`s mild weather was the result of upper level winds from the wouthwest and west. This pattern transported enough moisture inland from the Pacific for almost daily showers, including 2 inches of snow on the 7th, which quickly melted.
Offshore, an upper level trough was poised to move inland, and it finally did on the 11th. It brought cooler air, but no precipitation for Boise as it headed south to California and northwest Mexico.
Following this trough, an upper level high pressure ridge built over the northwest states. Cool air left behind by the trough was capped by warmer air aloft in the ridge, forming a shallow temperature inversion.
Enough moisture was present in the valley for the formation of late night and morning fog from the 13th through the 16th.
By the 16th the ridge had moved east, leaving strong southwest flow aloft ahead of yet another upper level trough. A weak disturbance moving through this flow brought enough instability and wind to break the inversion, and by afternoon the temperature had rebounded to above normal. The high of 58 degrees at the Boise Airport that day was the warmest reading of the month.
Before the trough moved inland on the 22nd, more weak disturbances brought daily showers, and the first thunder since October 2016 was heard on the 16th and 19th.
The trough lingered over the inter mountain region from the 22nd through the end of the month, keeping temperatures below normal.
Highs failed to rise above the 30s from the 23rd through the 27th, and snow flurries were an almost daily occurrence. On the 28th a disturbance from the Gulf of Alaska strengthened as it moved into the trough. It generated an inch of snow which covered the ground early that morning, but it was gone by the end of the day.