06 January 2014
Mid-morning in Madison, Wisconsin. Sunny, clear skies. Air temperature -20F/-29C. Wind chill -45F/-42C. (source, source)
The map below shows tomorrow's expected temperatures in terms of the difference from normal (scale at right):
It's interesting to note how the Great Lakes provide a thermal buffer as this arctic front passes - just as in the summer they provide regional cooling during heat waves.
I worry about the butterflies and their eggs and pupae. But perhaps their predators will also be impacted.