It was one of the milder Decembers. Only eight Decembers were warmer in the 80 years of airport records. No temperature records were broken or tied.
The temperature rose above freezing every day except the 29th, when the high at the airport was 32 degrees. However, nearby Boise locations warmed into the mid-30s that day. Normally there are 7 days in December when highs fail to exceed 32 degrees.
The relatively warm weather was due the absence of long lasting temperature inversions, and a pattern which kept arctic air east of The Rockies.
The 22nd was the warmest day with 61 degrees, under strong southwest flow aloft ahead of an upper level trough. It was also the windiest day, with a gust of 36 miles per hour from the southeast.
Precipitation was half an inch below normal. Snowfall was less than half normal. The greatest snow depth was 1 inch on the 2nd. The average December has 7 days with an inch or more on the ground.
The precipitation deficit was due to a tendency for storm systems to move south over California, rather than moving east over our area.
Nearly half of December’s precipitation fell from the 11th through the 14th, when a brief pattern change allowed moist westerly flow aloft to push inland over the northern intermountain region.
Across southwest Idaho and southeast Oregon, it was a common theme of above normal temperatures and below normal precipitation and snow.