In an unusually early and strong warning, national weather forecasters cautioned Friday that conditions are ripe for violent tornadoes to rip through the nation from Texas to Minnesota this weekend.

As states across the middle of the country prepared for the worst, storms were already kicking off in Norman, Okla., where a twister whizzed by the nation’s tornado forecasting headquarters but caused little damage.

It was only the second time in U.S. history that the Storm Prediction Center issued a high-risk warning more than 24 hours in advance, said Russ Schneider, director of the center, which is part of the National Weather Service. The first time was in April 2006, when nearly 100 tornadoes tore across the southeastern U.S., killing a dozen people and damaging more than 1,000 homes in Tennessee.

This weekend’s outbreak could be a “high-end, life threatening event,” the center said.