Winter (December 1-Feb 28) is the fastest warming season across all of the Midwest with most places experiencing 10-15 more above average winter days than just 50 years ago. In 1970, Iowa could expect about 40 above average days in the winter, but now that number is over 50 days. In more than 10 of the past 50 years there have been 60 or more above average days in the winter, but more than half of that number has occurred since 2000.
Even though winter is showing a dramatic warming trend, that doesn’t mean there won’t be days with below zero temperatures or months that end below average. But, the total number of extremely cold days and the number of days in a cold snap is shrinking.
In 1970, the average length of the longest winter cold snap in Des Moines was around 19 days, but that average is now down to 11 days. The longest cold snap in the 2020-2021 winter was 17 days, and that was the longest streak in more than 5 years. The 2014-2015 winter season also saw 17 days with below average temperatures.
Another way to look at this warming trend is through the coldest temperature of the year. Since 1970 the overall coldest low temperature has risen by over 6° in Des Moines…but it’s still cold! That average lowest temperature went from -16° in 1970 to -10° in 2020. In the past 10 years the low temperature has ranged from 1° to -20°.
A warmer winter will lead to a number of negative impacts in health, recreation, and the economy. Exposure to disease-carrying pests like mosquitoes will increase as they are able to survive for a longer period of time. Seasons may also shrink for ice fishers and skiers, which would result in less money for local companies.