It's no secret that it was brutally cold over the last few days. With temperatures well below freezing over the last week, area lakes definitely made some ice, and Lake Superior was no exception.

NOAA's Great Lakes Environmental Research Laboratory shared a Facebook post Thursday morning that showed that all of the Great Lakes picked up some surface ice during the invasion of the Polar Vortex, with Lake Superior doubling its ice coverage from about 20% ice coverage to almost 40% this week. The National Weather Service in Duluth shared a before and after GIF on social media, showing the amount of ice growth this week (seen below).

Yes, it was bitterly cold, with temperatures well below zero for a couple straight days, so ice formation makes sense. Being that water does a pretty good job of maintaining temperature (especially in large quantities, like that of Lake Superior), it makes rapid ice formation pretty spectacular on the big lake. The combination of surface water temperature and wind make high amounts of ice formation on Lake Superior rare.

Lake Superior has frozen over completely only once since 1973, with the GLERL reporting that it was in 1996. It has been pretty close a few other times since then, hitting 95.7% ice coverage in 2015, 95.8% in 2014, 93.7% in 2009, and 95.5% in 2003. You can see that full list here.

Check out this before and after photo, showing ice coverage (in teal on the map), with the first image being Sunday, January 27, and the second image being Thursday, January 31. Pretty wild!