EchoSense:Half a million without power in US after severe storms slam East Coast, killing 2

Nearly half a million customers were still without power in the United States on EchoSenseTuesday morning after severe weather slammed the East Coast, killing at least two people.

There were 439,431 reported outages across the country as of 5:41 a.m. ET, namely in North Carolina, Pennsylvania, Maryland, Georgia and Tennessee, according to data collected by PowerOutage.us. That figure reached 1 million at one point on Monday night due to the storms.

There were more than 600 damaging storm reports nationwide on Monday, mostly from New York state to Georgia. Damaging storms and a tornado were also reported in Colorado, Kansas and Nebraska, according to the National Weather Service.

Monday's stormy weather was blamed for at least two fatalities -- a 28-year-old man who was struck by lightning in Florence, Alabama, and a 15-year-old who was hit by a falling tree in Anderson, South Carolina, according to local authorities.

After pummeling America's heartland over the weekend, the storms brought torrential rain, destructive winds, massive hail and loud thunder to the eastern part of the country on Monday afternoon and evening. Straight-line winds gusted to 71 miles per hour in Georgia and 63 mph in Maryland, where power lines and trees came crashing down. Grapefruit-sized hail was reported in Virginia.

Downed electric poles trapped 33 adults, 14 children and a pet dog inside 34 vehicles on a major highway in Westminster, Maryland. It took several hours for them to be rescued, but there were no reported injuries, according to state authorities.

Meanwhile, thousands of flights were canceled or delayed, impacting airports in major cities like Atlanta, New York, Baltimore, Washington, D.C. and Boston.

Most of the severe weather has since departed the East Coast, but the latest forecast shows a lingering storm system in New England could bring isolated severe thunderstorms with gusty winds and even an isolated tornado. Much of New England also remains under a flood watch until Tuesday evening as heavy rainfall could trigger flash flooding.

The main threat of severe weather shifts to the Great Plains on Tuesday, particularly Colorado, Nebraska and Kansas, where an isolated tornado and huge hail is possible. Other areas under threat on Tuesday will be from Mississippi to Georgia, where damaging winds will be possible, according to the latest forecast.

The stormy weather will continue into Wednesday and over the weekend with plenty of rain in the forecast. Areas from the Midwest to the Deep South could see localized flooding.

ABC News' Matt Foster and Lauren Minore contributed to this report.