Severe thunderstorm threat for millions in eastern US

Millions are under threat of severe thunderstorms on Saturday in the eastern U.S., from Alabama into the Northeast.

The primary hazards from any severe thunderstorms that move through are strong, potentially damaging wind gusts, and large hail. Isolated tornadoes are also possible.

Any stronger, slow-moving thunderstorms bringing torrential rain could also trigger areas of flash flooding and bring frequent lightning.

There is the potential for numerous severe thunderstorms across Pennsylvania and in parts of New York state and Ohio.

A tornado watch also remains in effect for parts of Ohio, Pennsylvania and New York through the afternoon and early evening hours, including in Cleveland, Pittsburgh and Syracuse.

A severe thunderstorm watch has been posted across portions of Tennessee, Alabama and Georgia. Damaging wind gusts and large hail are the main concerns.

In Mt. Juliet, Tennessee, a lightning strike is believed to have caused a massive fire at an apartment complex in the Nashville suburb Saturday afternoon, authorities said.

The residents of the building were able to safely evacuate unharmed, though a firefighter who got caught in the building as it began to collapse was transported to an area hospital with serious injuries, police said.

On Sunday, the severe weather threat is focused over the center of the country, stretching from the Texas Panhandle to western Kentucky and Tennessee.

The primary hazards from any severe thunderstorms that move through the region will be strong, potentially damaging wind gusts and large hail. However, an isolated tornado or two cannot be ruled out.

Dangerously hot conditions

Meanwhile, extreme heat continues to be a threat across much of the country.

Millions in the South are still dealing with extreme heat, as parts of the Northwest now brace for dangerously hot conditions in the coming days. Heat alerts have been issued for more than 95 million Americans, stretching from Washington State to Florida.

In the South, an excessive heat warning is in effect for parts of Texas, Mississippi, Louisiana and Florida, including in Dallas, Austin, Houston, Jackson, New Orleans and Orlando.

A heat advisory is in effect for cities such as Little Rock, Arkansas; Memphis; Atlanta; and Miami.

Dangerously hot conditions are expected to impact much of the South Saturday afternoon with heat index values forecast to top 105 degrees in many cities. In some locations, it will feel like 110 to 115 degrees. Daily record highs will be challenged from Texas to Florida.

Temperatures will be heating up in the coming days along the West Coast. Highs this weekend are expected to soar into the triple-digits up across the Central Valley of California, from Sacramento to Redding.

Dangerous heat is then expected to expand up across parts of Oregon and Washington, with afternoon temperatures forecast to hit the triple-digits in some spots early next week.

An excessive heat warning goes into effect Sunday for parts of Oregon, including Portland, Eugene and Medford. An excessive heat watch has been posted for early next week in Seattle, Washington.

Record highs will be challenged early next week across portions of western Oregon, including Portland, and into Washington. Highs could hit the triple-digits for three days in a row in Portland.