The risky business of severe weather
Severe weather season is in full swing and when there is a risk of severe weather, meteorologists will tell you the risk level. But what do the different risk levels actually mean?Different risk levels are used when estimating the danger and forecast confidence. Three risk levels commonly used by the Storm Prediction Center of the National Weather Service are Slight, Moderate and High risk.Meteorologists understand the actual definitions of these risk levels but many times the public does not. This could lead to a misinformed audience of people who need to make personal decisions based on the forecast.For example a slight risk of tornadoes for a given area is actually a much more dangerous situation than the classification might suggest.Even a five percent chance of tornadoes will grab a meteorologist TMs attention and prompt them to be more focused on the chance of tornadoes.It TMs important to know just what the risk levels are for severe weather situations so let TMs start with the slight risk.From the National Oceanic and Atmospheric Administration:SLIGHT (SLGT) risk:A SLGT risk implies that well-organized severe thunderstorms ARE expected but in relatively small numbers and/or small areal coverage, or a small chance of a more significant severe event. Not all severe storm events will be covered with a SLGT risk, especially during the summer when short-lived, "pulse-type" severe storms are relatively common during the afternoon.
How about a MODERATE (MDT) risk:A MDT risk implies a greater concentration of severe thunderstorms, and in most situations, greater magnitude of severe weather and greater forecaster confidence compared to a SLGT risk. A MDT risk is usually reserved for days with substantial severe storm coverage, or an enhanced chance for a significant severe storm outbreak. Typical MDT risk days include multiple tornadic supercells with very large hail, or intense squall lines with widespread damaging winds.
Finally, a HIGH risk:The HIGH risk implies that a major severe weather outbreak is expected, with large coverage of severe weather and the likelihood of extreme severe (i.e., violent tornadoes or very damaging convective wind events). The HIGH risk category is reserved for the most extreme events with the least forecast uncertainty, and is only used a few times each year.