The TOR:CON values range from 0 to 10. A value of 4 means that there is about a 40% chance of a tornado within 50 miles of a location in the specified area of severe thunderstorm activity. This also means that there is a 60% chance that a tornado will NOT occur. Higher values mean there is a greater likelihood for tornadoes. But for many parts of the U.S., the average daily chance of a tornado within 50 miles is 4% or less even at the peak time of year, so even low TOR:CON values are meant to indicate and elevated – but not guaranteed – threat of a tornado nearby.
Description of TOR:CON values:
0 – near-zero chance of a tornado or severe thunderstorm nearby
2 – very low chance of a tornado nearby, but hail or strong wind gusts possible
4 – low chance of a tornado nearby, but hail and/or strong wind gusts possible
6 – moderate possibility of a tornado in the area of concern
8 – high probability of a tornado in the area of concern