Temperature - Maximum, 1981-2010 Monthly Average

Based on daily observations from 1981-2010, colors on the map show the long-term average maximum temperature in each climate division for the month displayed. The map reveals the average of “afternoon high” temperatures during the month over the previous three decades.

Temperatures for each month come from stations in the Global Historical Climatology Network. A combination of volunteer observers and automated instruments collected the highest temperature at each station every day from 1981 to 2010, and sent them to scientists at the National Center for Environmental Information (NCEI). After scientists checked the data quality to omit any systematic errors, they calculated each station’s average monthly maximum temperature: they took the sum of all the maximum temperatures and then divided by the number of days in the month times 30 years. NCEI scientists plotted the values for each station on a gridded map; to calculate values for other points on the grid, a computer program applied a scientifically reviewed mathematical filter to account for the distance between stations and variations in elevation. The average of all grid point values within each climate division is the long-term average maximum temperature for that division.

The color in each climate division shows the average of the highest temperature recorded every day of the month for the 30 years from 1981 to 2010. Shades of blue show where the highest daily temperatures measured across a climate division from 1981 to 2010 averaged below 50°F for the month. The darker the shade of blue, the lower the temperature. Climate divisions shown in shades of orange and red have long-term average maximum temperatures above 50°F. The darker the shade of orange or red, the higher the temperature. White or very light colors show climate divisions where the average maximum temperature is 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.