OKLAHOMA CITY>> A least two people drowned when their vehicles were caught in floodwaters in Oklahoma on Wednesday as slow-moving thunderstorms inundated roads across parts of that state and Texas, authorities said, while Pennsylvania residents picked up from a powerful storm that left three people dead.

Heavy rains and severe thunderstorms will mean a heightened risk of flash flooding across the south-central U.S. through today, the National Weather Service said.

The storms drenched much of southern Oklahoma and northern Texas, flooding and washing out roads and causing hundreds of flights to be canceled or delayed at major airports.

One man drowned in Oklahoma after his vehicle got swept off a Pottawatomie County highway, said Sheriff Freeland Wood.

“My deputy went in to try and save him, and he got caught up in the same mess,” Wood said.

The deputy was treated at a hospital and released, Wood said. Floodwaters closed nearly three dozen roadways in the county.

Another drowning was reported in neighboring Lincoln County after a driver’s vehicle got trapped in floodwaters along a highway northwest of Prague, said Oklahoma Highway Patrol spokesperson Sarah Stewart.

Authorities in the state reported numerous drivers were rescued from floodwaters, while some residents in the small city of Lexington evacuated their homes as the waters rose.

Oklahoma City set a record on Wednesday with 11.94 inches of rain in April, surpassing the 1947 mark of 11.91 inches, said Oklahoma State Climatologist Gary McManus.

Oklahoma was poised to break the 1942 record for statewide rainfall average of 8.32 inches for April, McManus said.

In the Dallas area, departures were grounded at Dallas Love Field and Dallas-Fort Worth International Airport for part of the day because of thunderstorms, according to the Federal Aviation Administration.

Hundreds of flights were canceled at DFW International Airport and dozens more at Love Field, according to FlightAware.

Tuesday night’s powerful storm knocked out power to more than 425,000 customers in Pennsylvania and 40,000 in Ohio, according to PowerOutage.us. Neighboring states also reported thousands of outages. Nearly 300,000 Pennsylvania customers and about 27,000 in Ohio were without power late Wednesday.

A spokesperson for Pittsburgh-based Duquesne Light called the storm’s damage “unprecedented” for knocking out electricity for some 250,000 of its customers and toppling trees and snapping power poles. The utility was bringing in outside help to restore electricity, and outages could last a week, the spokesperson said.

“This is a natural disaster, folks, the level of which we don’t see very regularly,” said Matthew Brown, the emergency services chief for Pennsylvania’s Allegheny County.

Authorities say three deaths are related to storms in Pennsylvania.