The Categorical Outlook is the Storm Prediction Center (SPC) risk map that sums up the Day 1, 2 and 3 Convective Outlooks in five numbered severe levels: 1 Marginal, 2 Slight, 3 Enhanced, 4 Moderate and 5 High. A separate general thunderstorm area outlines a 10 percent or higher chance of thunderstorms.
How the levels are set
SPC converts its hazard probabilities into these levels using published conversion tables. Since 03/03/26, those tables also take in Conditional Intensity Groups, so the same probability can land at a different level depending on expected intensity.
For example, a 10 percent tornado probability converts to Slight without an intensity group and to Enhanced with CIG1. A 30 percent tornado probability converts to Moderate with CIG1 and to High with CIG2.
SPC said the categories themselves stayed the same through this change. What changed is how a forecast reaches them.
What each level means
In SPC's descriptions, Marginal covers severe storms that are short-lived and loosely organized, or very sparse. Slight means organized severe storms are expected, though usually in low coverage.
Enhanced marks a greater concentration of organized severe storms. Moderate points to potential for widespread severe weather with several tornadoes and/or numerous severe storms, some possibly intense, and High means SPC expects a severe weather outbreak.
SPC lists the average yearly frequency at or above each level as about 14 days for Moderate and 2 to 3 days for High.
How to read a categorical map
The category is a good starting point for planning. Staffing, travel and chase decisions can all begin with the level and then move to the details.
Two Enhanced days may not look alike on radar, but the level still places a day between Slight and Moderate in expected coverage and intensity.
What the category does not tell you
A Slight Risk driven by hail plays out differently from one driven by tornadoes. Check the hazard probabilities and intensity groups behind the color before drawing conclusions.
Category lines are drawn on a map, and the atmosphere does not respect them. Storms can occur just outside a risk area, so being outside the line is not a reason to ignore storms that are forming.