Extreme weather in parts of US gets rarely-used 'high risk' designation

The high-risk designation signals severe weather with intense, long-track tornadoes or thunderstorms bringing hurricane-force winds and widespread damage

A dynamic storm system threatening to spawn powerful tornadoes and hail as big as baseballs has earned a relatively rare designation from forecasters: A high risk day of severe weather.

Parts of Missouri, Iowa and Illinois saw some of the most extreme weather on Friday, with the system forecast to take aim Saturday at southern states including Louisiana, Mississippi and Alabama.

Numerous significant tornadoes, some of which should be long-track and potentially violent, are expected on Saturday afternoon and evening, the federal Storm Prediction Centre said in its latest forecast.

Magenta marks areas at highest risk

The Storm Prediction Center uses five categories to warn of expected severe weather, ranging from marginal to high. Its forecast maps are colour-coded, with the lowest risk areas in green and the highest shown in magenta.

On Saturday, that area of highest risk includes parts of Mississippi and Alabama.

The high risk designation is used when severe weather is expected to include numerous intense and long-tracked tornadoes" or thunderstorms producing hurricane-force wind gusts and inflicting widespread damage, according to the agency's product descriptions.

On many days when the high risk designation was used in recent years, the forecasts became reality.

2024 Kansas and Oklahoma tornado outbreak

On May, 6, 2024, the Storm Prediction Centre assigned the high-risk category to parts of Kansas and Oklahoma, warning of multiple significant tornadoes along potentially long paths.

The forecast was prescient, as dozens of tornadoes gouged the landscape. One of the strongest twisters tore through the small town of Barnsdall, Oklahoma.

Aerial video showed many homes reduced to piles of rubble. About 25 people were rescued from homes where buildings had collapsed on or around them, the town's mayor said at the time.

2023 Mississippi River Valley tornadoes

On March 31, 2023, the Storm Prediction Centre outlined two areas along the Mississippi River Valley at high risk for tornadoes.

Hours after that forecast was issued, multiple twisters collapsed a theatre roof during a heavy metal concert in Illinois and shredded homes and shopping centres in Arkansas.

A roof collapse at the Apollo Theatre in Belvidere, Illinois, killed one person and injured more than two dozen others. About 260 people were in the venue at the time, the local fire chief said.