Temperature - Mean, 1981-2010 Monthly Average

Based on daily observations from 1981-2010, colors on the map show the long-term average mean temperature in each climate division for the month displayed. The maps show mean temperatures—the arithmetic average between the highest and lowest temperature in a 24-hour period—averaged together over the month for the previous three decades.

Temperatures come from daily measurements at stations in the Global Historical Climatology Network. A combination of volunteer observers and automated instruments collected the highest and lowest temperatures at each station every day from 1981 to 2010, and sent them to scientists at the National Center for Environmental Information. After scientists checked the data quality to omit any systematic errors, they calculated each station’s average monthly mean temperature and plotted it on a gridded map. To fill the grid, a computer program applied a mathematical filter to account for the distance between stations and differences in elevation. The average of all grid point values within each climate division is reported as the long-term average mean temperature for that division.

Shades of blue show where a climate division’s average mean temperature from 1981 to 2010 was below 50°F for the month. The darker the shade of blue, the lower the average mean temperature. Areas shown in shades of orange and red had long-term average mean temperatures above 50°F. The darker the shade of orange or red, the higher the average mean temperature. White or very light colors show climate divisions where the average mean temperature during the three decades from 1981 to 2010 was near 50°F.

Understanding these values provides insight into the “normal” conditions for a month. This type of information is widely used across an array of planning activities, from designing energy distribution networks, to the timing of crop and plant emergence, to choosing the right place and time for recreational activities.

Data Snapshots are derivatives of existing data products: to meet the needs of a broad audience, we present the source data in a simplified visual style. This set of snapshots is based on climate division data (nClimDiv) produced by and available from the National Centers for Environmental Information (NCEI) - Weather and Climate. To produce our images, we run a set of scripts that access the source data and display them on our base maps.

These monthly maps represent the base period conditions against which single months are compared for Data Snapshots Difference from Average Temperature Monthly images of the contiguous United States.