Q: When was Madison's coldest day?

A: Sunday was the 60th anniversary of the coldest day ever recorded in Madison: January 30, 1951.

The temperature that day reached an astounding 37 degrees below zero.

To get that cold, a lot of circumstances have to be in place. First, a fresh and relatively deep snow cover is a great help as snow radiates infrared energy exceptionally well. With the long nighttime hours of mid-winter, by the end of the night, a lot of energy has been radiated away from the surface of the snow, chilling the air just above it. During the last week of January 1951, widespread moderate snows affected the southern portion of our state. 

Second, crystal clear nights are needed to maximize the amount of energy loss near the surface. The night of January 29-30, 1951, was crystal clear in Madison as a strong surface high pressure system was centered over Dubuque, Iowa. The proximity of the surface high also ensured that the air near the ground was nearly calm overnight. The calm winds prohibit vertical mixing of the air, again working toward keeping the near surface temperature as cold as possible. In fact, on the morning of January 30, the air temperature about 2 miles above the ground was minus-18 — a full 20 degrees warmer than the air at the surface.

Had there been even light winds that night, some of that warmer air could have mixed to the surface and kept the temperature from getting as cold as it did.

That we have now gone 60 years without breaking this record testifies to the sensitivity of low temperature to such exacting circumstances. If this record is ever broken, it will surely be as a result of the subtle interplay of these variables. 

Steven A. Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) the last Monday of each month at 11:45 a.m.

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