Rapid City, SD We've seen the sub-zero numbers on thermometers all day.
So, we did some experiments to show just what freezing really looks like.
Dr. Steve Miller said "First of all, we would recommend that if you don't have to be outside that you stay inside where it's warm."
And there's good reason for that.
We heated up two bowls of chicken noodle soup to about 115 degrees - then set them both outside - one with a hat covering - the other, without.
In just 5 minutes, 115 degrees dropped to about 53.
But with a hat on, the soup sat at about 75, which goes to show why you should wear a hat before braving the cold.
Wind chills reached about as low as negative 40 degrees this morning according the National Weather Service.
And it can take as quickly as 10 minutes to get frostbite in this weather.
This wet t-shirt quickly froze in just about 5 minutes outside - on the surface, a chilly negative 29 degrees.
Dr. Miller said "If you have to be outside working - you can still sweat in these cold temperatures especially if you're bundled up. And staying dry is very important when it's this cold."
And what if you bring boiling water out to the cold?
Black Hills FOX reporter Robert Grant said "It is negative 12 degrees outside and in temperatures like this ... water turns to vapor."
We also set a bowl of water outside - this time lapse shows the water beginning to freeze over - all in just under 30 minutes.
And you might want to start your car before getting inside - the temp on the seat - about 0 degrees.
Fortunately, we may have seen the worst, Saturday - those thermometers will heat up overnight.
Saturday's high temperatures are the coldest Rapid City has seen in 3 years.