AccuWeather.com

By Alex Sosnowski, Expert Senior Meteorologist

Jul 7, 2011; 10:30 AM ET

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The Normals include such weather phenomena as temperature, precipitation, wind, atmospheric pressure and dew point temperature.

"The new Normals indicate warming overall during the 30-year period across the nation in both maximum and minimum temperatures."

The prior 30-year Normals from 1971 to 2000 have now been replaced by the new Normals from 1981 to 2010, by the National Oceanic and Atmospheric Administration (NOAA).

Every 10 years, the NOAA releases new Normals for many parameters of the weather.

The term "Normal" is simply an average over a recent 30-year period.

Data from thousands of observation sites across the U.S. are gathered and maintained by the National Climatic Data Center (NCDC), which is part of the NOAA.

Since temperature is a "hot" topic these days, we will focus on that alone in this article.

The new Normals will have no effect on record temperatures. For example, a record high set in 1938 for a particular date will remain on the books, unless actually eclipsed by surging temperatures on that date. However, the adjustment will affect daily and monthly temperature departures.

Changes in high temperatures averaged throughout the year.

The new Normals indicate warming overall during the 30-year period across the nation in both maximum and minimum temperatures.

Changes in low temperatures averaged throughout the year.

Removed from the average is the relatively cooler decade of the 1970s and replaced by the warmer decade of the 2000s. The difference, about +1.5 degrees, had a warming influence on the new Normals, by about +0.5 of a degree.

According to climatologists at NCDC, "The replacement of Normals provides some evidence of climate change. However, care must be taken when interpreting changes between one Normals period and the other."

Climatologists NCDC go on to point out that the trend could be due to changes in instrumentation, movement of the observation site, methodology and more.

Interestingly, every month was not warmer everywhere.

There was a slight cooling trend in July high temperatures over parts of the Northeast, Plains and Mississippi Valley. A common cause of lower high temperatures in the summer is cloudy conditions during all or part of the day and/or higher moisture levels in the soil.

January lows indicated a slight cooling trend in the Southeast.

However, a trend toward much warmer July nights, on average, was observed from the Upper Midwest to the northern Rockies. A common cause of warmer low temperatures at night is extensive cloud cover.