On February 10, arctic air across a ground covered in snow and ice led to the coldest temperatures seen in Indiana since January 2009. Parts of the state approached 20 degrees below zero. Back in 2009, several areas across northern Indiana actually fell below -20 degrees.
|Young America 3 ESE||-14|
|West Lafayette 6 NW||-13|
|Crawfordsville 6 SE||-12|
|Tipton 5 SW||-10|
|Farmland 5 NNW||-10|
In order for these conditions to appear, clear skies and very light or calm winds are necessary. This was the case the morning of February 10 across Indiana as high pressure had moved into the area.
Below is an infrared satellite picture of the area taken at 7:15 AM EST. These images are enhanced with color to show where the colder temperatures are. When there are clouds around, colder temperatures usually indicate clouds higher in the atmosphere (such as the top of a thunderstorm). However, in this case, skies were clear, so the satellite was seeing cold temperatures from the ground. Click the image for a larger version.
The yellowish colors show where the coldest air was across the area. The white data on top of the satellite image are surface observations for 7:00 AM. The top left number of each observation is the temperature. For example, the temperature at Indianapolis was 0 degrees while the temperature at Lafayette was -7 degrees.
Below is a visible satellite picture taken at 12:31 PM EST. Few clouds were present, so the white seen on the picture is snow and ice cover. Most of the area is covered with snow or ice, even down across Kentucky and Tennessee. Temperatures dipped below zero as well in Kentucky where snow was present. More information on the cold across the southern USA is available from the NWS Louisville.
A map of observed low temperatures from across the state of Indiana follows below. Note that areas across southern Indiana that do not have snow cover remained above zero. (Click the image for a larger version)