Darrell Spangler, via Associated Press

It’s official, although not necessarily a surprise. The average temperature across the contiguous United States for the first six months of this year has been the warmest on record — and by a considerable sum — dating back to 1895, according to a monthly report released Monday by NOAA’s National Climatic Data Center.

The average 2012 temperature through June was 57.4 degrees Fahrenheit — 4.5 degrees higher than the long-term average for the same period. That’s 1.5 degrees warmer on average than the second hottest temperatures recorded, in 2006, said Jake Crouch, a climate scientist at the data center.

Most of the overall increases occurred east of the Rocky Mountains, where it mixed with extremely dry weather.

Swaths of the Central Plains, Ohio Valley, and Mid-Atlantic states were drier than average. In fact, the percentage of the lower 48 states experiencing drought increased from 37 percent (representing the long-term average) to 56 percent in the first half of 2012. The report characterized it as the largest area of drought seen in the 21st century.

Colorado, where recent wildfires consumed forests and homes, is included in this area of drought. Colorado’s temperature in June was 6.4 degrees higher than its historical average.

The heat in June was probably the result of an extremely dry winter in the state, said Kevin Trenberth, a climate analyst at the National Center for Atmospheric Research in Boulder, Colo., a federally funded research and development center. This winter, Colorado’s mountains had the lowest snow pack in the last 40 years, snow that disappeared quickly in spring and early summer.

“By the beginning of June, there was no snow in the Rocky Mountains in Colorado,” said Dr. Trenberth. “That’s unprecedented, to my knowledge.”

He said the reported temperatures are “consistent with the view that climate change is playing a role” in weather patterns.

NOAA’s climate analysis report for June, four pages long, did not mention climate change. Mr. Crouch said that at the center, “We focus on just putting the facts out there” rather than suggesting causes for the patterns.

Since snow helps keep the atmosphere cool by reflecting heat back into space, less snow means warmer temperatures. It also means there’s less moisture circulating in the environment from snow melt. Both of these factors increase the risk for wildfires. The worst wildfires to sweep Colorado before this year occurred in 2002, when the second lowest amount of snow pack was recorded in the mountains there.

Dr. Trenberth said the dryness in Colorado not only increased the risk of wildfires but also led to the formation of the hot air mass that moved east across the states late last week.

The southeast, which some climate data has shown is warming more slowly than the rest of the country, had a very warm June as well. While the area started off cool, by the end of the month South Carolina and Georgia recorded what might be their hottest statewide temperatures to date, with daily highs reaching 113 and 112 degrees, respectively. “We tend to see those kinds of records broken in July and August and not in June,” said Mr. Crouch.

Mr. Crouch said extremes like those in South Carolina and Georgia are important indicators of overall climate trends and that the NCDC has seen an increase in record-breaking nighttime and daytime high temperatures in the past few years across the nation.

The climate is complicated, however, so not everyone felt the heat. The report said that first half of the year for Washington, Oregon and Minnesota was one of the wettest and coolest on record.

“A country the size of the U.S. is almost never hot everywhere, all at once,” said Dr. Trenberth. The most significant thing about the NOAA climate report is that it tells of so many all-time records for heat being broken, he said, adding, how hot it is on a given day is not as important as the historical records that are being consistently broken.

“This is part of a longer-term pattern that’s certainly evident this year, where we’ve gotten the warmest year on record,” said Dr. Trenberth.