DOI: 10.3886/e235146v1
title: Climate.gov Data Snapshots: Temperature - Maximum, 1991-2020 Monthly Average

description: <b>Q: How warm do afternoons usually get during this month?

 </b><b>A: </b>Based
 on daily observations from 1991-2020, colors on the map show the 
long-term average maximum temperature, sometimes referred to as the 
daytime or afternoon high, in 5x5 km grid cells for the month displayed.
 The map reveals the average of daytime high temperatures during the 
month over the previous three decades.

 
 <br><b>Q: Where do these measurements come from?
</b><b>
 </b><b>A: </b>Daily
 temperature readings come from weather stations in the Global 
Historical Climatology Network (GHCN-D). Volunteer observers and 
automated instruments collected the highest temperature at each station 
every day from 1991 to 2020, and sent them to the National Centers for 
Environmental Information (NCEI). After scientists checked the quality 
of the data to omit any systematic errors, they calculated each 
station’s average monthly maximum temperature by taking the sum of all 
the daily maximum temperatures for a month (for example, all Junes in 
the 1991-2020 period) and dividing it by the total number of daily 
measurements (the number of days in the month times 30 years). NCEI 
scientists then plotted the values on a 5x5 km gridded map. To fill in 
the grid at locations without stations, a computer program interpolated 
(or estimated) values, accounting for the distribution of stations and 
various physical relationships, such as the way temperature changes with
 elevation. The resulting product is the NOAA Monthly U.S. Climate 
Gridded Dataset (NClimGrid).

 
 <br><b>Q:</b><b> What do the colors mean?</b>
 <b>A:</b> The
 color in each 5x5 km grid cell shows the average of the highest 
temperature recorded every day of the month for the 30 years from 1991 
to 2020. Shades of blue show where the highest daily temperatures 
measured from 1991 to 2020 averaged below 50°F for the month. The darker
 the shade of blue, the lower the temperature. Areas 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 areas where the average maximum temperature 
is near 50°F.

 
 <br><b>Q: Why do these data matter?</b><b>
 </b><b>A:</b> 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.

 
 <br><b>Q: How did you produce these snapshots?</b><b>
 </b><b>A:</b> 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 NClimGrid climate data produced
 by and available from the National Centers for Environmental 
Information (NCEI). To produce our images, we invoke a set of scripts 
that access the source data and represent them according to our selected
 color ramps on our base maps.

 
 
 <br><b>Additional information</b>
 The data used
 in these snapshots can be downloaded from different places and in 
different formats. We used this specific data source:

NClimGrid Temperature Normals<br>
 

 
 <b>References
 </b>
 NOAA Monthly U.S. Climate Gridded Dataset (NClimGrid)<br>
NOAA Monthly U.S. Climate Divisional Database (NClimDiv)<br>
Improved Historical Temperature and Precipitation Time Series for U.S. Climate Divisions)<br>
NCEI Monthly National Analysis)<br>
Climate at a Glance - Data Information)<br>
NCEI Climate Monitoring - All Products
 <br>Source: https://www.climate.gov/maps-data/data-snapshots/data-source/temperature-maximum-1991-2020-monthly-a...<br><br>This upload includes two additional files:<br>* Temperature - Maximum, 1991-2020 Monthly Average _NOAA Climate.gov.pdf is a screenshot of the main Climate.gov site for these snapshots (https://www.climate.gov/maps-data/data-snapshots/data-source/temperature-maximum-1991-2020-monthly-a...)<br>* Cimate_gov_ Data Snapshots.pdf is a screenshot of the data download page for the full-resolution files.<br><br><br>
description: Data is divided in to folders by image resolution -- full size (zip), kml (zip), broadcast (png), small (png), and large (png). <br><br>Data downloaded from climate.gov 6/15/2025 - 6/16/2025 (small, large, and full resolution) and 6/21/2025 (broadcast and kml).<br><br>