January thaw: Mild weekend, shot at 40 on Sunday

Our January thaw is on the way. January thaws have become a part of the Minnesota weather lexicon. But what defines a January thaw? And just how common are they?

First, we deal with one more frigid day behind the breezy cold front that cleaned up our Minnesota air quality. Air quality index values dropped dramatically Thursday as northwest winds blew in fresh Canadian air.

The index for fine particles reached as high as 161 Tuesday evening, and has plunged into the good range at 41 Thursday afternoon.

Friday brings less wind, some mixed sunshine and more typical January temperatures.

January thaw this weekend

Southwest winds bring milder air into Minnesota starting Saturday afternoon. Highs should crack the thawing point across much of southern Minnesota Saturday.

Sunday will be the warmest day. Highs will push the 40-degree mark Sunday afternoon in the south.

I still think temperatures on the map below are a few degrees too conservative Sunday afternoon. I think we’ll see lots of 40-degree temperatures from the Twin Cities south and west Sunday afternoon.

Monday brings another day above the thawing point, with a chance for some light rain or snow showers.

What’s a January thaw?

A January thaw is defined as two or more days with highs above 32 degrees, according to the Minnesota Climate Working Group.

Just how frequent are January thaws in Minnesota? Believe it or not they are more frequent than a white Christmas in the Twin Cities.

January Thaws occur in about 94 percent of years dating back to the late 1800s. We’re now on a streak of 12 years and counting with January thaws. The last year without a January thaw in the Twin Cities was 2011.

Here’s more detail on January thaws from the Minnesota State Climatology Office:

A January Thaw is defined as two or more consecutive days with maximum temperatures above 32 degrees F. These thaw episodes are a regular part of Minnesota's climate, bringing a brief respite to a Minnesota winter. January Thaws are most common and often most dramatic in southwestern Minnesota, where the local topography can boost daytime temperatures above freezing with relative ease, and sometimes even above 60 F. Although less extreme, January Thaws also occur most years throughout southern and western Minnesota.

In the Twin Cities, January Thaws occur 94% of the time. For comparison, a "White Christmas" in the Twin Cities (one inch or more of snow cover on Christmas Day) occurs about 72% of the time, meaning we are more likely to have a January Thaw than a White Christmas, and this is true in all but the northern third or so of the state.

With at least one January Thaw now recorded in 2022, the streak is currently 11 years and counting; the last winter without a January Thaw in the Twin Cities was 2011.

The longest January Thaw on record in the Twin Cites is 18 days, spanning January 13th through 30th of 1944. That run of warm weather included a reading of 58 degrees F on the 25th, which still stands as the warmest January day on record in Minneapolis.

January Thaws exhibit some interesting long-term behavior, especially given the unmistakable trends in recent winters. For instance, January is Minnesota's fastest-warming month, with temperatures across the state increasing by 8-10 degrees F between 1970 and 2021. Yet the frequency of January Thaw events remains largely unchanged, and the length of these events shows no sign of increasing.

For instance, of the seven thaw events lasting 10 days or more in the Twin Cities, only one, in 1981, occurred during the period of modern winter warming, and each of the other six occurred prior to the end of World War II! This suggests that winter's dramatic warming trend is taking place without dramatically increasing the number of January Thaw days. The relationship between relatively cold and relatively warm days has not changed appreciably. What has changed, is the average temperature on any day. Cold days and warm days alike are now generally warmer, and often much warmer, than they had been historically.