Very warm air aloft, just above a strong and shallow surface inversion, was able to "mix down" on Monday allowing for temperatures to soar to record levels at a number of locations across Iowa. Sioux City was able to reach a high 75°F, which beat the record high temperature for 9 February by a 13°F margin! The featured chart presents the record maximum high and minimum low temperature beat margins. Note that the low temperature beat margins are presented as negative values for plotting legibility / comparison. One has to go a considerable way back to find a larger high temperature beat margin. 29 Feb 1992 would be a candidate at 14°F, but being leap day makes the record margin perhaps less significant as the period of record of that calendar date is much smaller. 7 Feb 1987 at 17°F is next date with a larger margin, so either way it has been a while!