Daily Climate Extremes Tool

The Daily Climate Extremes Tool provides information on a variety of extreme climatological conditions for stations across the United States. This tool can answer questions such as:

• On average, when is the warmest day of the year for this location?
• On average, how hot is the warmest day of the year for this location?
• What is the coldest temperature ever recorded at this location?
• For this location, what time of year receives the least amount of precipitation on average?

Using the Tool

The Applied Climate Information System (ACIS) provides access to data from over 4,200 daily weather stations across the U.S., enabling users to visualize temperature, precipitation, and snowfall records, as well as highest and lowest daily normals. Users can tailor the map display through various filtering options. By selecting the Symbolize feature, accessible via the layer stack icon on the left side of the tool, users can apply filters to view weather station extremes. Stations, represented by colored dots, will automatically populate the map based on the selected criteria. Note that not all U.S. stations are available in this tool. The dot color corresponds to the legend when clicking the button with three horizontal lines.

Available filters include:

• Highest/Lowest - Highest or lowest occurrences.
• Record/Normal - All-time daily records or 1991-2020 daily climate normals.
• Maximum Temp/Minimum Temp/Precipitation/Snowfall - The variable of interest (Maximum Temperature, Minimum Temperature, Precipitation, or Snowfall).
• Value/Date - Whether to display the extreme value or its corresponding date.

When a station is selected (by clicking on a dot), a table on the right side of the tool will automatically populate with relevant data. The Daily Normals and Daily Records tables will be displayed regardless of the filters applied. However, depending on the selected filters, certain cells may remain empty. For example, if a user filters to view only records for a specific variable, the station may not have daily normals for that variable, resulting in a blank Daily Normals table. Similarly, if certain variables are not measured at the station, they may appear missing in the Daily Records table, simply indicating that the data for those variables are not available at that location.

Methodology

Stations must have no more than 10% of daily data missing for the selected weather variable to appear in the Daily Climate Extremes Tool. Since not all stations record every weather variable, certain stations may be excluded when applying specific filters. This ensures that only the most complete and accurate data are displayed.

Notes and Disclaimers

Users should note the station's period of record when looking at extreme values. Shorter record periods may result in values differing from nearby stations.

Certain selections for this tool will result in maps without meaningful information.  For example, selecting lowest record precipitation date will present a map that displays the day of the year in which the lowest record precipitation was recorded.  This is not meaningful as all locations often experience the lowest possible daily precipitation amount of 0.00 inches several times throughout the year.  The same is true for the options of lowest record snowfall date and lowest normal snowfall date.