Overcast skies provided some relief Friday for hundreds of thousands of Americans who had no electricity to run air conditioners as the United States sweated through a week of stifling heat.
At least 20 deaths in several states have been blamed on temperatures that hovered in the high 30s C.
With more than 300,000 homes and businesses still without power in and around St. Louis, Mo., National Guard troops, police, firefighters and volunteers were knocking on doors and offering bottled water as they checked on elderly residents.
"I think, for the most part, all the residents we checked on were doing all right," Mitchell Kester, spokesman for the Guard's 1140th Engineering Battalion, said Friday.
Gov. Matt Blunt sent troops to St. Louis on Thursday, the same day Mayor Francis Slay declared the city a disaster area.
On Wednesday, a massive storm knocked out power to more than half a million customers, followed by heat that topped 35 C.
By Friday morning, 415,000 homes and business were still without power, utility company AmerenUE said. The company said it could be four days before all power is restored.
At least 20 deaths linked to heat
The heat wave sizzled much of the nation this week and has been blamed for at least 20 deaths, including that of a 93-year-old St. Louis woman who was found dead in a home without power to run the air conditioning.
Medical examiners were determining whether the death of a 92-year-old Independence, Mo., man whose air conditioning had stopped working was heat-related, and an East St. Louis, Ill., man died while walking near downed power lines.
Other deaths were reported in Illinois, Pennsylvania, Oklahoma, Arkansas, Indiana, South Dakota, Tennessee, Kansas and Wisconsin.
Friday's high was only expected to hit 30 C, with another round of thunderstorms possible. Forecasters expect the milder weather to continue into next week.
Around the region, people began cleanup from Wednesday's storms that brought 130 km/h winds and heavy rain. In St. Louis, the storms tore off a section of airport roof and dumped it on a highway.
Windows were blown out of a hotel restaurant and a press box at baseball's Busch Stadium. At least three buildings collapsed, and more than 30 people were injured.
Mysterious electrical problem plagues New York
In New York, some 100,000 people have suffered through five days of blackouts that blamed on a mysterious electrical problem.
The power outages have taken place over a span that included two of the hottest days of the year.
An estimated 25,000 customers remained without power, Consolidated Edison said in a statement.
Con Edison initially said fewer than 2,000 customers were affected, but it increased that number tenfold on Friday morning.
Mayor Michael Bloomberg estimated that 25,000 customers would translate to about 100,000 people, considering that each "customer" could be more than one household in an area where homes are often sectioned into multiple units, and could even be an entire apartment building.
"The sad thing is, this shouldn't have happened," Bloomberg said. "We don't know why, but the most important thing [is to] make sure nobody dies or gets hurt and then help Con Ed to get it back up."
The New York blackouts started Monday in a handful of neighbourhoods in Queens. Two LaGuardia Airport terminals lost power Monday night and again on Tuesday.
Since then, hundreds of businesses have been idle, and the city's jail complex on Rikers Island has operated on backup generators. Some building's elevators were not running, and traffic lights at some intersections were not working.