A popular measure of cold weather is the number of days with temperatures falling to zero degrees or lower. The number of subzero days this winter (through March 7) have varied from 15 at Shenandoah to 50 at Decorah while typical seasonal totals vary from 10 to 30 days across Iowa.
Not only has the three mid-winter months been unusually cold, so was the late fall of 2013. The second one-half of October averaged 4.9 degrees colder than usual (coldest for the period since 2006). November 2013 averaged 2.9 degrees colder than normal (coldest since 2000). Additionally the first six days of March have averaged 20.4 degrees colder than usual (coldest start to March since 1962).
The persistent cold has allowed the soil to freeze to unusually great depths, despite abundant snowfall which acts to insulate the ground from the colder air above the snowpack. National Weather Service measurements indicate that soils under sod have frozen to a depth of about two to three feet while Iowa DOT data shows the frost depth has extended as much as five and one-half feet beneath roadways. The good news is that the depth of frozen ground has reached its maximum for the winter. The thaw will primarily begin at the surface but there likely will also be a very slow thaw at the base of the frozen soil layer. The best guess is that soils will be completely frost free by about April 10 statewide. Unusually warm and/or rainy weather would accelerate the rate of thaw while persistent cold or snow could delay the thaw even further.
While the cold has been very persistent and widespread over the winter, the amount of snow fall has been highly variable across Iowa. Snow totals so far this winter have been as much as 50% less than usual across portions of far western Iowa while the southeast corner of the state has seen about double the usual amounts. County snowfall averages vary from 15 inches in Montgomery County of southwest Iowa to 57 inches in Fayette, Clayton and Buchanan counties of northeast Iowa. The statewide average snow fall stands at 36.0 inches and already exceeds the long-term average with about six weeks of the snow season remaining. This marks the seventh snow season of the past eight with greater than normal snowfall (the long-term snowfall average is 31.0 inches).