New Delhi, April 15 -- A long-lasting weather pattern is poised to blast hot air like a furnace across the eastern United States, with the unusual heat wave threatening to shatter record high temperatures on Wednesday in big cities including New York, Philadelphia and Washington, D.C.

The heat is unusual for April, not only because it's scorching much of the nation so early in the year but also for its duration. The near-record temperatures are expected to last into this weekend, forecasters say.

The potentially dangerous heat comes after severe storms tore through Kansas, Minnesota and Wisconsin on Monday, and more storms threaten Tuesday in the nation's midsection.

While it's not unprecedented to see high temperatures climb toward 90...