(CNN) -- The mainland United States, which was largely recovering Monday from a near-nationwide heat wave, has experienced the warmest 12-month period since record-keeping began in 1895, the National Oceanic and Atmospheric Administration said Monday.
High temperatures during June also contributed to a record-warm first half of the year, the agency said in its monthly analysis. The heat during the last half of June broke or tied 170 all-time high temperature records in cities across the lower 48 states.
"Temperatures in South Carolina (113 degrees) and Georgia (112 degrees) are currently under review by the U.S. State Climate Extremes Committee as possible all-time statewide temperature records," NOAA said.
The average temperature for the mainland in June was 71.2 degrees -- two degrees above the 20th-century average and the 14th warmest June on record.
The state of Colorado, which saw several large wildfires, had its warmest June ever, NOAA said. The warmest-ever June experienced nationwide was in 1933.
The heat wave, which stretched across much of the nation for more than a week, was largely history Monday, but the break in the heat could mean severe storms in some areas, forecasters said.
A cold front was working its way through the Mid-Atlantic states, dropping high temperatures into the 80s in cities including Chicago, New York, Boston and Washington.
The heat wave that roasted much of the country for more than a week left scores dead and millions without power at one point -- many of them following a round of severe storms that swept through the Mid-Atlantic states on June 29.
The nation's capital set another record Sunday with a high of 102 degrees -- the city's 11th straight day of temperatures over 95.
Other high temperatures Sunday included 105 in Raleigh-Durham, North Carolina, which tied an all-time record; 103 in Richmond, Virginia; 101 in Charlotte, North Carolina; and 100 in Baltimore.
Nationwide, there have been more than 4,500 daily record highs in the past 30 days, according to the National Climatic Data Center.
However, the forecast high for Washington on Monday was 86. Other forecast highs were 87 in Baltimore, 90 in Richmond and 90 in St. Louis.
Portions of North and South Carolina will be the last to escape the heat, as a heat advisory remained in place for some locations Monday. Monday's forecast high for Raleigh was 97 with a heat index as high as 104; Tuesday's forecast predicts a high of 87 degrees.
But the cold front brings a chance of severe weather, particularly across the eastern Carolinas and southeastern Virginia, CNN meteorologist Sarah Dillingham said. More than 160 wind reports were received nationwide as the front worked its way eastward, she said.
Damaging winds were the main threat of Monday's storms, she said. A "slight risk" area included the cities of Norfolk and Roanoke, Virginia, along with Raleigh, Charlotte and Wilmington, North Carolina.
On Sunday, damaging winds struck Fredericksburg, Virginia, and collapsed a building, injuring two people, according to the National Weather Service's Storm Prediction Center. The storms have complicated restoration efforts in some spots and caused even more damage. One person died Saturday in storms in Cuba, Missouri, the prediction center said.
"It has been a tough few weeks for many Virginians," Gov. Bob McDonnell said late Sunday. "They have suffered from record-breaking temperatures and an historic storm that brought widespread damage and power outages. Now, many have lost power again. I ask Virginians to remain patient and to continue to help each other get through this latest storm."
Just under 100,000 customers in 11 states and metropolitan Washington were without power as of Monday. Some have lacked electricity for more than a week after the June 29 storms.
More than 72,000 of those customers were in West Virginia, the hardest-hit state. Because utility companies typically define each residential and business account as a customer, the actual number of people affected was higher.
Outages in metropolitan Washington, however, had dropped to 316 Monday morning.
More hot weather may be on the way, forecasters warned. The National Weather Service issued excessive heat warnings for parts of Arizona and California starting Monday, predicting temperatures in the range from 110 to 115 degrees.
"The combination of hot afternoon temperatures and very warm overnight lows will result in oppressive conditions," the weather service said.
High temperatures Monday were expected to reach 102 in Redding, California; 98 in Sacramento, California; 104 in Fresno, California; 100 in Salt Lake City; 115 in Yuma, Arizona; and 113 in Phoenix.
The Pacific Northwest, however, experienced cooler than average temperatures in June, according to the NOAA. Cooler conditions were also present in the Southeast, despite record-breaking heat in late June.