WeatherStorm Tracker Blog


Understanding the Severe Risk Categories

Posted at 8:55 AM, Apr 13, 2019

Each day the Storm Prediction Center issues a severe risk outlook, which highlights the areas across the country that have a threat for severe storms. The outlook includes five different categories – marginal, slight, enhanced, moderate, and high.

Each category is tied to the possibility of a severe weather event withing 25 miles of a particular location. A severe thunderstorm must produce at least one of the following: wind gusts of at least 58 mph, hail at least one inch in diameter, or a tornado. The severe thunderstorm risk categories can reflect the intensity of a severe event, the probability of severe weather, or the number of severe thunderstorms.

What does each category mean?

marginal risk means isolated severe thunderstorms are possible. Severe events are limited in duration and/or coverage and/or intensity.

slight risk is a two out of five, meaning scattered severe storms are possible. Thunderstorms are short-lived and/or not widespread. Isolated intense storms are also possible.

For days when numerous severe storms are possible, an enhanced risk will be posted. More persistent and/or widespread storms are expected. A few intense storms are also possible.

moderate risk means widespread severe storms are likely. These thunderstorms may be long-lived, widespread, and intense.

Finally, when widespread and particularly intense severe thunderstorms are expected, the SPC outlook will include a high risk.

In the case of today’s severe potential, a moderate risk has been put out for extreme eastern Texas, central Louisiana, and west-central Mississippi. This is the area that SPC forecaster expect will have the greatest potential for severe storms. Damaging winds, several tornadoes, and large hail are possible threats.

The very same system will produce another severe threat Sunday, and this time it will be closer to home. The Day 2 outlook includes an enhance risk over the entire LEX 18 viewing area plus much of Appalachia. Strong to severe thunderstorms may come in two waves Sunday – one in the morning and a second during the afternoon. A potent low will push into western Kentucky very early in the morning. A line of storms will reach I-75 just before sunrise. Damaging winds and heavy rain will possible. There may be a small window around mid-day to catch a break, allowing the atmosphere to recover. If the atmosphere does get a chance to recharge, additional severe thunderstorms could develop into the afternoon and evening. At this time all severe threats are the table – damaging winds, large hail, isolated tornadoes, and heavy rain. Stay tuned for another update later today.