A "particularly dangerous situation" tornado watch is in effect for Wednesday evening by NOAA's Storm Prediction Center (SPC) for eastern Arkansas, northwest Mississippi, northeast Louisiana and western Tennessee until 8 p.m. CST. This type of tornado watch is issued in rare situations when long-lived intense tornadoes are likely, according to the center's experts. This is just the beginning of what's expected to be multiple days of dangerous storms that will move east through Christmas Eve. 

Severe thunderstorms already caused multiple tornadoes near Clarksdale, Miss., Wednesday. A tornado also occurred in Greenwood, Ind. Wind damage and hail to the size of baseballs was received in parts of Arkansas, southeast Missouri and Illinois Wednesday morning.

One person has already died in Arkansas and several others were injured in Tennessee as a result of these storms.

The threat will increase and become more widespread in parts of the South and Ohio Valley as the tornado outbreak gets under way.

The Tornado Conditions Index, better known as TOR:CON, has been raised to as high as 8 out of 10 for parts of west Tennessee, northern Mississippi and northern Alabama on Wednesday, meaning there's a 80 percent chance of a tornado within 50 miles of any location in the indicated area. Tornadoes and damaging winds will also be possible in a much larger area from the Gulf Coast to the Ohio Valley. This includes TOR:CON values as high as 7 in eastern Arkansas, 6 in west Kentucky and south Mississippi, and 5 in southeast Missouri and northeast Louisiana.

As millions of holiday travelers hit the road, officials warned that fog and rain could cause major problems for drivers in unfamiliar areas, USA Today reported. The fog already has caused three deaths in a southwestern Arkansas pileup that occurred late Monday night.