The hibernal ecological season corresponds to the winter calendar season. In our area it is characterized by cold temperatures, a usually snow-covered landscape, and an absence of migratory bird species. Deciduous trees are bare and fallen leaves begin to decay. Migrating birds have settled in winter habitats. In Minnesota the hibernal season usually begins about December 1 and lasts until about March 1.
The average date for the first one-inch snow fall in the Twin Cities is November 18. The average date for “permanent snow cover” in the Twin Cities is unknown but is probably mid-December. Permanent snow cover here is defined as at least one centimeter of snow cover that lasts at least one month.
On November 10, 2014, Minnesota was hit with its first major snow storm leaving a snow cover that has persisted and will probably be with us until at least December 10.
On average, cold temperatures arrive in the Twin Cities on December 3. On that date the average high temperature is below freezing. The first stretch of cold weather arrived with the November 10 snowfall. The unscientific term “stretch of cold weather” here is defined as a week with more daily high temperatures below freezing than above. Between November 11 and November 20 the temperature (in Lakeville) did not rise above 24°.
This year the winter calendar season will begin on Sunday, December 21, at 5:03 p.m. CST. By that time the hibernal season, whether determined by snow cover or by daily temperature, will have been with us in the metro area of Minnesota for six weeks.