NASHVILLE, Tenn. (WKRN) — Winter has officially arrived, and not just because it says so on the calendar but also because the temperatures prove it. As Tennesseans bundle up for the big chill that has hit the area, the National Weather Services (NWS) has already issued a Wind Chill Warning through midnight Dec. 23.

There could be other alerts issued by NWS. Here’s a list of key winter weather-related terms and alerts as well as what they mean.

An advisory means to be aware. A watch means to be prepared. A warning means to take action.

Wind Chill

Wind chill factors the combined effect of the temperatures and the wind and how that makes people and animals feel cold. The Wind Chill Index is based on the rate of heat loss due to exposed skin, according to the NWS. The speed of wind and dropping temperatures can cause the body to lose heat rapidly, eventually causing hypothermia.

Wind Chill Advisory

A Wind Chill Advisory is issued when seasonably cold wind chill values are expected but do not reach extreme conditions.

Wind Chill Watch

A Wind Chill Watch is issued when the combination of cold temperatures and strong wind could reach dangerous levels in the next 12 to 48 hours. NWS suggested avoid going outside, but if you do, then to dress warmly, to have at least a half tank of gas in your car, and to update your winter survival kit.

Wind Chill Warning

A Wind Chill Warning is issued when extremely cold temperatures and strong winds combined could reach dangerous levels or are occurring. NWS suggested avoid going outside, but if you do, then to not only dress warmly but to also let someone know where you are going and to update them when you arrive. NWS also said to dress in layers and cover exposed skin. Wind Chill Warning levels could lead to frostbite and hypothermia in a matter of minutes.

Freezing Rain

Freezing rain happens when rain freezes when it hits the ground, which can create a coating of ice, according to the NWS.

Sleet

Sleet occurs when rain turns to ice pellets before hitting the ground. It can also cause water on the roads to freeze over creating icy conditions, according to the NWS.

Winter Weather Advisory

A Winter Weather Advisory is issued when snow, blowing snow, ice, sleet or any combination of those could possibly occur.

Winter Storm Watch

A Winter Storm Watch is issued 24 to 72 hours out from a winter storm event which could include heavy sleet, heavy snow, ice or any combination of those.

Winter Storm Warning

A Winter Storm Warning is issued when a winter storm event is occurring including heavy snow, heavy sleet, ice, blowing snow or any combination of those hazards. The weather could make traveling impossible and is not encouraged.

Ice Storm Warning

An Ice Storm Warning is issued when ice is expected to accumulate at least 1/4 inch or more. NWS said an ice storm could lead to snapped powerlines and falling trees. Travel is extremely dangerous in these conditions.

Blizzard Warning

A Blizzard Warning is issued when severe winter weather conditions are expected or occurring with wind gusts equal to 35mph or greater are combined with falling/blowing snow. Conditions also have to frequently reduce visibility of 1/4 mile for three hours or more. The whiteout conditions make traveling extremely dangerous and if you must travel, NWS suggested to have a winter survival kit, and to stay with your car if you get stranded until help arrives.