Name File Type Size Last Modified
  data 06/24/2025 09:03:PM
Climate_gov_ Data Snapshots.pdf application/pdf 11 MB 06/17/2025 06:08:PM
Historic Probability of Severe Weather _ NOAA Climate.gov.pdf application/pdf 1.3 MB 06/17/2025 06:08:PM

Project Citation: 

National Oceanic and Atmospheric Administration. Climate.gov Data Snapshots: Historic Probability of Severe Weather. Ann Arbor, MI: Inter-university Consortium for Political and Social Research [distributor], 2025-06-24. https://doi.org/10.3886/E233242V2

Project Description

Project Title:  View help for Project Title Climate.gov Data Snapshots: Historic Probability of Severe Weather
Summary:  View help for Summary
Q: Where is severe weather likely at this time of year?

A: Shading on each map reflects how often severe weather occurred within 25 miles during a 30-year base period. The darker the shading, the higher the number of severe weather reports near that date. For this map, severe weather encompasses tornadoes, thunderstorm winds over 58 miles per hour, and hail larger than three-quarters of an inch in diameter.

Q: How were these maps produced?

A: For each day of the year, scientists plotted reports of severe weather from 1982 to 2011 on a gridded map. To reveal the long-term patterns of these events, they applied mathematical filters to smooth the counts in time and space. Keep in mind that severe weather is possible at any location on any day of the year.

Q: What do the colors mean?

A: Shaded areas show the historical probability of severe weather occurring within 25 miles. Meteorologists estimated these probabilities from severe weather reports submitted from 1982-2011. For each day of the year, scientists plotted reports of severe events onto a map marked with grid cells 50 miles on a side. For each grid cell, they counted the number of years with at least one report, and divided by the total number of years. To reveal the long-term patterns suggested by this relatively small dataset, they used statistical methods to smooth the data. For instance, to smooth clusters of events in time, a mathematical filter replaced the value in every grid cell with a 15-day average. Another filter extended report locations over a 25-mile-wide circle to indicate the probability that the event could have occurred at other points within that area.

Q: Why do these data matter?

A: Knowing when and where severe weather tends to occur through the year promotes preparedness. Residents who are alert to the possibility of severe weather are better able to respond in ways that keep them safe. These data can also help emergency response personnel plan for when and where their services may be necessary.

Q: How did you produce these snapshots?

A: 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. NOAA's National Weather Service Storm Prediction Center produced the Severe Weather Climatology files. To produce our images, we obtained the climatology data as a numpy array, and ran a set of scripts to display the mapped areas on our base maps with a custom color bar.

Additional information
Data for these images represents an update and extension of work first put forth by Dr. Harold Brooks of the National Severe Storms Laboratory.

References
Brooks, H. E., C. A. Doswell, III, and M. P. Kay, (2003) Climatological estimates of local daily tornado probability, Wea. Forecasting, 18, 626-640.




This upload includes two additional files:
* Historic Probability of Severe Weather _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/historic-probability-severe-weather )
* Cimate_gov_ Data Snapshots.pdf is a screenshot of the data download page for the full-resolution files.


Original Distribution URL:  View help for Original Distribution URL https://www.climate.gov/data/SevereWeather--Daily--Historic-Probability-of-Severe-Weather--CONUS/

Scope of Project

Subject Terms:  View help for Subject Terms severe weather; climate; climate change; weather history
Geographic Coverage:  View help for Geographic Coverage United States
Time Period(s):  View help for Time Period(s) 1982 – 2011
Data Type(s):  View help for Data Type(s) images: photographs, drawings, graphical representations
Collection Notes:  View help for Collection Notes One image for each day of the year.

Data is divided in to folders by image resolution -- full size (zip), kml (zip, broadcast (png), small (png), and large (png). Occasionally there may be one image missing in a particular size but available in another size.

Data downloaded from climate.gov 6/15/2025 - 6/16/2025 (small, large, and full resolution) and 6/21/2025 (others).


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