Kevin Myatt is The Roanoke Times' weather columnist.

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Normalcy is being redefined today.

Every 10 years, the National Weather Service updates its normal temperature and precipitation data to reflect the average of the past 30 years.

Today, the years from 1981 to 2010 will become the new period used to calculate normal temperatures and precipitation for thousands of stations across the United States, including Roanoke and Blacksburg. The 1981-2010 period will replace the 1971-2000 period that has been used for the past decade, and will remain the standard until the 1991-2020 period replaces it in 2021.

Temperature norms have been calculated for about 7,500 stations and precipitation norms for 8,700 stations, according to preliminary information released by the National Climatic Data Center. For the first time ever, the new climate norms will not only include annual, monthly and daily figures, but hourly norms for 260 stations.

The new norms generally, though not in every specific case, are warmer than the old ones. That will bring up questions about the role of global warming in the changes.

On a question-and-answer website devoted to the new normals, the National Oceanic and Atmospheric Administration advises that changes in climate norms provide only a "crude metric of climate change impacts," and that changes between the two data sets for any particular site "may be due to station moves, changes in methodology, urban heating, etc. that are not reflective of real changes in the underlying climate signal."

Nevertheless, the administration also notes that temperatures on average are a half-degree warmer (Fahrenheit) across the U.S. in the new norms than they were in the 1971-2000 data set, and that annual average highs and lows are warmer in all of the 48 contiguous states (the preliminary information makes no statement about Alaska and Hawaii).

According to maps released preliminarily by the climate data center, normal July high temperatures for Southwest Virginia will not change much with the new climate norms, but January lows will be warmer by about a degree.

Normal January lows will be 2 to 4 degrees warmer over the Dakotas, Minnesota, Wisconsin and parts of several surrounding states. January low norms for 1981-2010 are at least half a degree above the 1971-2000 norms for almost all of the continental 48 U.S. states except for the Southeast, where there is little change. The only location where January norms are slightly lower is in parts of Florida.

Normal July highs are up to 1.5 degrees higher in most of the Rockies and Pacific Northwest, and also up to a degree above normal in the Washington, D.C., area. Normal July highs are about a degree cooler in most of Missouri and parts of surrounding states. Most other areas of the country show little change.

The 1970s featured some of the most widespread outbreaks of severe cold in U.S. history, particularly the latter part of the decade. Five of Roanoke's only 11 months since 1912 to average below 30 degrees occurred in the 1970s, including the coldest monthly average on record, 23.6 degrees in January 1977.

So it's not surprising that dropping the 1970s out of the data set would significantly raise normal temperatures in the winter.

As more of the data becomes publicly available, I'll take a closer look in weeks and months ahead at more specifics in the changes at the local level.

Weather Journal runs on Monday, Wednesday and Friday.