Severe Thunderstorm Risk Categories
When there is a risk for thunderstorms or severe storms, we usually categorize those risks on a 5-tier system, such as the one below...
When we forecast a risk for GENERAL thunderstorms, no severe storms are expected, but some storms may produce frequent lightning, some flooding, winds up to 40mph, or small hail.
A MARGINAL risk includes a threat for isolated severe storms. These severe storms don't last more than an hour and are limited in coverage and intensity. Winds with the strongest storms are typically 40 to 60mph, hail may be as large as quarters, and the tornado threat is low.
During a SLIGHT risk, scattered severe storms are forecast. These severe storms are short-lived and not widespread. The strongest storms often produce damaging winds, hail up to the size of hen eggs, and may produce tornadoes.
An ENHANCED risk for severe storms means there will be numerous severe storms that are more persistent and widespread. Some storms may be intense. There will be several reports of damaging winds, large hail, and up to a few tornadoes may be confirmed.
A MODERATE risk for severe storms means severe storms are likely. Severe storms will be long-lived, widespread, and intense. Damaging winds are likely with the strongest storms. Hail is often large and destructive. The strong storms will be rotating and may produce strong tornadoes.
A HIGH risk for severe storms means that a severe weather or tornado outbreak is likely. Severe storms will be widespread and intense. A derecho - a long-lived complex of storms producing damaging winds - is possible. Hail will be large and may be very large. Tornadoes that develop may be strong or violent.
A MARGINAL risk includes a threat for isolated severe storms. These severe storms don't last more than an hour and are limited in coverage and intensity. Winds with the strongest storms are typically 40 to 60mph, hail may be as large as quarters, and the tornado threat is low.
During a SLIGHT risk, scattered severe storms are forecast. These severe storms are short-lived and not widespread. The strongest storms often produce damaging winds, hail up to the size of hen eggs, and may produce tornadoes.
An ENHANCED risk for severe storms means there will be numerous severe storms that are more persistent and widespread. Some storms may be intense. There will be several reports of damaging winds, large hail, and up to a few tornadoes may be confirmed.
A MODERATE risk for severe storms means severe storms are likely. Severe storms will be long-lived, widespread, and intense. Damaging winds are likely with the strongest storms. Hail is often large and destructive. The strong storms will be rotating and may produce strong tornadoes.
A HIGH risk for severe storms means that a severe weather or tornado outbreak is likely. Severe storms will be widespread and intense. A derecho - a long-lived complex of storms producing damaging winds - is possible. Hail will be large and may be very large. Tornadoes that develop may be strong or violent.