By JEFF MARTIN

ATLANTA (AP) — U.S. government forecasters are using a relatively rare “high-risk” designation — the highest category they use — to warn that a major tornado outbreak appears likely Wednesday in an area that’s home to about 2.5 million people.

That area most at risk of catastrophic weather on Wednesday includes parts of west Tennessee including Memphis; northeast Arkansas; the southeast corner of Missouri; and parts of western Kentucky and southern Illinois.

The Norman, Oklahoma-based Storm Prediction Center says that “multiple long-track EF3+ tornadoes, appear likely.” Tornadoes of that magnitude are among the strongest on the Enhanced Fujita scale, used to rate their intensity.

Historically, the “high-risk” designation has been used sparingly, but it did appear just a couple of weeks ago to warn of a deadly tornado outbreak in mid-March.

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 color-coded, with the lowest risk areas in green and the highest shown in magenta.

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.

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 Center 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 and then struck the larger community of Bartlesville.

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 Center outlined two areas along the Mississippi River Valley at high risk for tornadoes.

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

In all, 146 tornadoes from the 2023 outbreak were confirmed, making it the third-largest tornado outbreak on record in the U.S., the National Weather Service said. More than two dozen people were killed and dozens of others injured.