Another sizzling hot day for the eastern US before temperatures plunge 30 degrees

"It's still going to be, I think, pretty bad across the East,'' meteorologist Bob Oravec of the Weather Prediction Center said Wednesday morning. "I think today is probably the last day of widespread record potential. It might not be quite as hot as yesterday by a few degrees. But still, high temperatures are expected in the upper 90s across a good section of the East."

The weather service warned of "extreme heat" for a stretch of the country from North Carolina to New York and west to West Virginia. Highs could approach triple digits from New York to Richmond, Oravec said.

Temperatures Wednesday morning were "a little bit warmer than expected" because of northwesterly winds bringing "warm leftovers from yesterday," said former NOAA chief scientist Ryan Maue, a private meteorologist. Nantucket, Massachusetts, was above 90 degrees Fahrenheit (32 Celsius) when its forecast high was 82.

Weather whiplash

The high pressure heat dome that has baked the East was forecast to break. A cold front began moving south from New England, bringing with it clouds and cooler temperatures — not only cooler than 100 degrees Fahrenheit (38 Celsius), but cooler than normal.

That air mass drawing on cool ocean waters will send temperatures plummeting by the end of the week in Philadelphia, which hit a record high of 101 degrees Fahrenheit on Tuesday, said Ray Martin, meteorologist at the National Weather Service in Mount Holly, New Jersey. Air temperatures will be in the low 70s Fahrenheit (20s Celsius).

"It's going to feel like a shock to the system, but it's not anything particularly unusual," said Martin.

Boston's forecast high for Friday is 34 degrees lower than what it hit Tuesday.

"It's going to feel like a different season," Oravec said.

However, it won't last. After one or two days, slightly hotter than normal temperatures are forecast, but not anywhere near the highs from earlier this week, Oravec said.

Weather whiplash from one extreme to another occurs more often as the world warms overall from burning fossil fuels such as coal, oil and natural gas, scientists said.

Records smashed

Tuesday was likely the peak of the heat, with Baltimore the king of swelter. The city's high of 105 degrees Fahrenheit (40 Celsius) smashed a previous record by four degrees. At night, when the human body needs cooling, temperatures only dropped to 87 Fahrenheit (30 Celsius).

Baltimore was hardly alone. A dozen weather stations were 101 degrees or higher, including two New York airports. Boston hit 102, breaking its old record by seven degrees. Augusta, Maine's 100-degrees also broke its old record by seven degrees.

Every coastal state from Maine to South Carolina hit 100 degrees somewhere, with Georgia and Florida clocking in at 99 on Tuesday.

As temperatures rise "things become less reliable and more unstable," said Climate Central Chief Meteorologist Bernadette Woods Placky.

The heat meant more demand for power. The nation's largest power grid operator, PJM Interconnection, on Monday recorded its highest demand since 2011, with only a slight drop off Tuesday and Wednesday, spokesman Dan Lockwood said.

"We have an aging grid infrastructure already in United States, so you can see the impacts of that heat on that infrastructure," said Kate Guy, senior research fellow at the Columbia University Center on Global Energy Policy. The aging system is less capable of transmitting power at the voltages needed, she said. "At the same time, you're seeing a really big spike in demand. This is what they (utilities) are increasingly experiencing because of climate change," Guy said. "Frankly, with each year is increased, historic temperatures and that intense heat arriving earlier than ever, just putting an immense pressure on the electrical grid."

Extreme heat caused the road to buckle in two locations on an interstate highway in northern New Jersey. State transportation officials say the impact on the concrete roadway in Morris County on Tuesday afternoon forced some lane closures as temporary repairs were made. Crews then began work to replace the damaged areas and repave those sections.

Some downtown Chicago streets will close Wednesday night to repair pavement that has buckled due to hot temperatures amid an ongoing heat wave in the city.

"Pavement failures or blowouts occur when prolonged high temperatures cause the road to expand and buckle up or blow out, resulting in uneven driving surfaces," the Illinois Department of Transportation said in a statement.

In Chesapeake, Virginia, a heat-related malfunction prompted a bridge to remain stuck in the open position.