(Cincinnati, OH) -- Extreme cold temperatures are enveloping Greater Cincinnati.
The National Weather Service says many people are waking up to sub zero temperatures, with wind chills as low as 20 below.
A Wind Chill Advisory is in effect until 11 a.m. today.
When temperatures are this cold, frostbite can develop on exposed skin in as little as 30 minutes but the colder it is outside, the faster frostbite will occur.
Frostbite sets in when soft tissue in the skin begins to freeze and the most common areas affected include your extremities, like fingers, toes, nose and face.
Symptoms of frostbite include pain as well as discoloration around the infected area.
To prevent frostbite, limit your time outdoors in cold temperatures. If you need to go outside, keep your hands, ears and face covered and keep your clothes dry.
Hypothermia also is a risk when the temperature drops.
The brutal cold is forcing some schools in Cincinnati and the suburbs to close today.