The SPC issues probability maps for days 1 through 8, but in different forms. The day 1 always provides the probability of tornadoes, wind, hail, and the risk of severe weather. Days 2 and 3 only provide the risk and probabilistic outlook for any severe weather type. Days 4 through 8 provide only the probability of severe weather in general.
Severe weather is classified by the SPC in 6 ways:
General thunderstorms - weak thunderstorms, maybe a few with 40mph winds and small hail.
Marginal risk - chance of spotty damaging winds, spotty hail up to 1“, very low possibly a tornado in the area.
Slight risk - medium chance of having high winds of 60mph+, hail greater than 1”, low chance of a tornado in the area.
Enhanced risk - High chance of high winds 60mph+, hail greater than 1“, possibly larger than 2”, medium risk of a tornado in the area.
Moderate risk - very high chance of high winds 60mph+, hail greater than 1“, possibly larger than 3”, very high risk of a tornado in th area.
High risk - reserved for definite tornado outbreaks and derechos. Tornadoes almost definite in the area, including strong, long track varieties, winds greater than 70mph likely.
More detailed information about classifications can be foundhere.