Hands down the event of the decade was Morch 2012. The incredible magnitude of temperature departures over a gigantic area and for an extended period of time was unbelievable. Some locations exceeded their all time April high temps in March! There were also daily low temps that exceeded record highs for the date, and Chicago had 10 consecutive days of breaking/tying temp records
Some interesting bits from the Wikipedia article : ( https://en.wikipedia.org/wiki/March_2012_North_American_heat_wave )
In Traverse City, Michigan one day began with a low temperature (67 °F) that was higher than the previous record high for the day.
An 84 °F (29 °C) high at Madison, Wisconsin in early March was 43 °F (24 °C) above average and followed an overnight low of 60 °F, 35 degrees above normal[16] the daily high being more than seven standard deviations above the mean. The absolute temperature and departure statistically would be equivalent to a mid-July high at that station in excess of 125 °F or more; the highest temperature recorded there was 107° at least once during the heat waves of the middle 1930s
from Accuweather: ( https://www.accuweather.com/en/weather-news/amazing-stats-from-the-march-2-1/197377 )
26 The number of inches of snow that melted over the course of just seven days in Caribou, Maine, from March 15 to March 22, thanks to the unusual warmth. Also, 18 inches of snow was still on the ground when the first record high fell on March 18 (64 degrees).
32 The gap, in degrees, between the old and new record high on March 21 in Marquette, Mich. The new record high was 81 degrees, obliterating the old record of 49 degrees. The margin of defeat was so great that the low temperature that day was even higher than the old record high temperature.
from NWS:
" In fact, the warm spell which occurred during the middle of the month is perhaps the most anomalous weather event in Michigan since climate records began 130 years ago. " https://www.weather.gov/dtx/unprecedentedmarchwarmth2012