The recent month of April here in Madison was noteworthy on a number of levels.
First of all, we had snow on seven different days during the month, not quite the record of 13 from April 1950, but substantially above the average of about four days over the last 70-plus years.
Additionally, the month’s average temperature was 2.9 degrees below average — not a result of any particularly bitter days but a seemingly unending succession of cloudy and cool days. It is important to note that this daily average departure from normal of 2.9 degrees was the result of daytime highs being 4.7 degrees colder than normal and overnight lows being only 1.3 degrees below normal.
The cloudiness aspect of the past month’s weather can be directly assessed in comparison to recent Aprils through use of a heliometer, a device that measures the amount of solar radiation incident on the surface in units of watts per square meter.
Courtesy of calculations done by our colleague and department chair, professor Ankur Desai, it turns out that this past April was the “dimmest” April since in the last decade, registering an average of 287.28 watts per square meter (W/m2) during the daytime hours. Its nearest competitor for this unflattering distinction was April 2019, when the monthly daytime average was just 296.62 W/m2. The “brightest” April in the last decade occurred in 2015, when the daily average insolation was 377.82 W/m2.
So, if the past month seemed gloomy to you, you were absolutely correct in that assessment. It appears as though the coming week’s warmth and humidity will make us quickly forget that we had a protracted end to winter this year.
Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at firstname.lastname@example.org or email@example.com.