Tornadoes: Forecasting, Detection, and Communication

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Updated November 26, 2024

Tornadoes: Background and Forecasting

Tornadoes: Forecasting, Detection, and Communication

Updated May 30, 2025 (IF12695)

Tornadoes are narrow, violently rotating columns of air, extending fromconnecting the base of a thunderstorm to the ground. They affect communities across the United States every year. Tornadoes and can cause fatalities and injuries, destroy property and crops, and disrupt businesses. For example, a weather system on April 25-28, 2024, produced over 150A May 2025 weather system produced over 90 reported tornadoes (Figure 1), high winds, and large hail; it and caused multiple deaths and injuries across parts of the Midwest and South, according to preliminary estimates from the National Oceanic and Atmospheric Administration (NOAA).

Tornadoes have been reported on all continents except Antarctica. They occur most commonlythe Midwest and Southeast. The National Oceanic and Atmospheric Administration (NOAA) is the primary civilian federal agency with authority to issue severe weather forecasts and warnings. Congress may debate whether to direct the agency to take additional actions related to tornado forecasting, detection, and communication in light of recent and potential future storms. Exactly how and why tornadoes form is not completely understood. Tornado formation is believed to be dictated mainly by conditions in and around thunderstorms with well-defined circulation. Tornadoes have been reported on all continents except Antarctica. They are common in North America, particularly in the United States, which reports approximately 1,200 tornadoes per year based on official data dating back to the 1950s. Tornadoes occur across the United States but form frequently in three regions: (1) southern plainsthe Southern Plains (e.g., Texas, Oklahoma, Kansas), (2) the Gulf Coast (e.g., Alabama, Florida, Louisiana, Mississippi), and (3) northern plainsthe Northern Plains and upper Midwest (e.g., North and South Dakota, Nebraska, Iowa, Minnesota). Although tornadoes can form at any time, they occur mostly during spring and summer and usually duringin the late afternoon or early evening.

Classification

Experts estimate the strength or wind speed of a tornado by examining the damage it caused rather than by measuring actual wind speeds during an event. The Fujita, or F-scale, estimation method, developed in 1971, was used for over three decades, but its limitations prompted the development and adoption of a new scale in 2007, calledDamage is estimated using the enhanced F- scale,ujita-scale or EF-scale (Table 1). Table 1. Enhanced Fujita-Scale

EF Number	3-Second Gust (mph)
EF-0	65-85
EF-1	86-110
EF-2	111-135
EF-3	136-165
EF-4	166-200
EF-5	Over 200

(Table 1). The EF-scale uses 28 different types of damage indicators, such as building type, structures, and trees.

Table 1. Enhanced F-Scale

EF Number 3-Second Gust (mph)

0 65-85

1 86-110

2 111-135

3 136-165

4 166-200

5 Over 200

Source: NOAA, Storm Prediction Center, “Enhanced F Scale for Tornado Damage.” Notes: EF = Enhanced F-scale. A 3-second gust is estimated at the point of damage based on the EF-scale’s 28 damage indicators. The 3- second gust is not equivalent to wind speed measured in standard surface observations.

Figure 1. U.S. Tornadoes Daily Count and Running Annual Trend (as of November 25, 2024)

May 21, 2025)

Source: NOAA, Storm Prediction Center (SPC), “"Daily Counts and Annual Running Trend," May 21, 2025.

Notes: The red color denotes the 2025 U.S. daily numbers (bars) and "trend" or total number of preliminary tornadoes (line). The gray color denotes the 2005-2015 average daily numbers (bars) and annual trend (line). Preliminary tornadoes are tornadoes observed or reported from a variety of sources. SPC and local weather forecast offices analyze preliminary tornado reports to produce a final number (NOAA, National Centers for Environmental Information, "Index-Tornado Count").

The EF-scale uses eight levels of damage (e.g., beginning of visible damage to complete destruction) to various structures and trees. EF-0 to EF-2 tornadoes are most frequently reported in the U.S.

Forecasting, Detection, and Communication

The Secretary of Commerce, acting through NOAA's Administrator, is required to forecast weather and issueDaily Counts and Annual Running Trend,” November 25, 2024. Notes: The 2024 U.S. daily occurrence and trend for preliminary tornadoes is shown in red, and the average daily and annual trend (2005- 2015) is shown in gray. Because tornado reports come into forecast centers quickly, the trend for preliminary tornadoes reflects an estimate of the number of tornadoes. The National Climate Data Center and SPC analyze these reports to produce a final count, which may lower the count in cases where a tornado is reported more than once (NOAA, National Severe Storms Laboratory, “The Relationship Between Preliminary and Final Tornado Reports,” February 13, 2009).

Tornadoes: Background and Forecasting

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Forecasting, Detection, and Communication

Exactly how and why tornadoes form is not completely understood. Tornado formation is believed to be dictated mainly by conditions in and around rotating thunderstorms with well-defined circulation. The Secretary of Commerce, acting through NOAA’s Administrator, has authority for weather forecasting and for issuing storm warnings (15 U.S.C. §313), including tornado forecastingforecasts and warnings. NOAA’'s National Weather Service (NWS) provides these weather, water, and climate forecasts and warnings for the United States and its territories, adjacent waters, and ocean areas. Several other NOAA programs, including the National Severe StormsOffice of Oceanic and Atmospheric Research's National Severe Storms Laboratory, , also focus on tornado research to improve observations, modeling, and instrument developmentinstruments, among other activities.

Forecasting and Detection Severe thunderstorm and tornado forecasts are made by the The NWS Storm Prediction Center (SPC) and by local weather forecast offices (WFOs) each have roles in tornado forecasting and detection. (WFOs). SPC forecasters use weather observations, and numerical weather prediction models, and ensemble forecasting (models (i.e., running several models at one time) to determine if atmospheric conditions, temperature, and wind flow patterns may lead to the formation of severe weather. SPC issues three-day forecasts (convective outlooks) on a daily basis and analyses of the next six hours (mesoscale discussions) for severe weather potential. SPC issues a tornado watch if) on a daily basis and mesoscale discussions of severe thunderstorm potential for the next six hours, with an emphasis on the next one to three hours, as warranted.

If conditions favorable for either multiple tornadoes or a single intense tornado continue to develop, SPC issues a tornado watch, which; the watch typically lasts six to eight hours. Such watches alertSPC disseminates tornado watches to the public, emergency managers, storm spotters, broadcast media, and local WFOs that conditions have become favorable for the development of tornadoes. SPCand aims to issue watches at least two hours before the first tornado event.

Forecasters. WFO forecasters and storm spotters recognizelook for certain storm features from visual cuesfeatures, such as the forward or rear rear flank downdraft (Figure 2), and particular patterns in Doppler radar images, such as the tornadic vortex signature (a region of intense concentrated rotation) to identify tornadoes.

Figure 2. Selected Components of Certain Thunderstorms

Source: NOAA, NWS, "The Supercell Pt. 2."

Notes: A forward flank downdraft is the leading part of a supercell storm, with most of the heavy precipitation. A rear flank downdraft is a region of dry air sinking on the back side of, and wrapping around, a storm (NOAA, NWS, "Field Guide Glossary").

WFOs issue tornado warnings when a tornado has been sighted or indicated by weather radar. Warnings contain language about areas at risk, time frames, specific hazards, and recommended safety precautions for those at risk.

Communication

NOAA communicates tornado warnings to the public through outdoor sirens, local and cable television and radio stations, cell phone applications, Wireless Emergency Alerts, NOAA Weather Radio All Hazards (NWR), and the federal Emergency Alert System and Integrated Public Alert and Warning System.

Congressional Considerations

Congress may continue to consider whether to maintain or otherwise change NOAA's role in forecasting, detection, and communication of tornadoes in certain ways. For example, one bill in the 119^th Congress (S. 258) would evaluate the EF-scale; require a plan for use of "warn-on-forecasts" (an experimental project that relies on modeling and forecasts, rather than observations, to issue tornado warnings); amend NOAA's VORTEX-USA tornado program to "rapidly" improve tornado forecasts and warnings, and support additional physical and social science research. Some Members in previous Congresses have also introduced legislation and advocated for funding for other activities related to tornadoes, including next-generation radar and weather forecasting.

Congress may consider whether—and, if so, how—NOAA should study outstanding scientific questions. These include whether the number of tornadoes in the United States has increased over time, whether the timing and seasonality of tornadoes has changed, and whether climate change has impacted, or may impact, tornado frequency or intensity overall or in certain circumstances. For example, it is not clear whether tornadoes are occurring more frequently or whether they are being reported more often as a function of better detection, greater media coverage and verification efforts, a growing population, and the advent of cell phone cameras.

In addition, Congress may debate whether to conduct oversight of, reverse, amend, codify in statute, or take no action on changes the Trump Administration has made or proposed to federal agency staffing and funding across NOAA. For example, some news sources have reported that several NWS local WFOs no longer have 24-hour meteorologist coverage. The changes have been a part of efforts to decrease government spending; the effects of these changes on the agency are still unclear. Some current and former meteorologists and NWS directors have warned that such changes may impact NOAA's ability to forecast, detect, and communicate about impending tornadoes.

images, such as the tornadic vortex signature (a region of intense concentrated rotation). WFOs issue tornado warnings when a tornado has been sighted or indicated by weather radar. The warning contains specific language about areas at risk, time frames, specific hazards, and recommended safety precautions for those at risk.

Communication Several methods exist to communicate warnings to the public, including outdoor warning sirens, local television and radio stations, cable television systems, cell phone applications, Wireless Emergency Alerts, and NOAA Weather Radio All Hazards (NWR). NWS maintains and operates NWR, a nationwide network of radio stations broadcasting continuous weather information directly from the nearest WFO 24 hours a day, 7 days a week. NWR works with the Emergency Alert System, an automated system that allows NWS warnings to be disseminated by broadcasters, satellite digital audio services, direct broadcast satellite providers, cable television systems, and wireless cable systems.

Figure 2. Selected Components of Certain Thunderstorms

Source: NOAA, National Weather Service, “The Supercell Pt. 2.” Notes: A forward flank downdraft is the leading part of a supercell, with most of the heavy precipitation. A rear flank downdraft is a region of dry air subsiding on the back side of, and wrapping around, a cyclone (NOAA NWS, “Field Guide Glossary”).

Congressional Considerations

Congress may continue to consider options related to improving forecasting, detection, and communication of tornadoes to reduce the loss of life and property. Some Members have introduced bills that would amend a NOAA tornado program to “rapidly” improve tornado forecasts, predictions, and warnings and to evaluate and potentially update the current tornado rating system. The bills also would require a pilot program for tornado hazard communication, including the improvement of social, behavioral, economic, risk, and communication sciences, among other actions.

In a November 2024 letter to House leaders and appropriators, 24 Members requested additional funding for NOAA’s next-generation weather prediction system, including Radar Next, which may improve environmental data and products for “difficult-to-predict highly localized weather systems such as tornadoes.” Congress could consider additional support for federal research into the application of machine learning, an artificial intelligence technique, to improve tornado forecasts. Improved lead time for warnings may provide additional time for people to find shelter.

NOAA has estimated that in 2024, April had the second- highest tornado count on record and May had the highest count, surpassing the 550 tornados of May 2003. However, experts have difficulty discerning if the average number of tornadoes each year has changed over time or if tornados are being reported more often today as a function of better detection, greater media coverage and verification efforts, more storm spotting and chasing, a growing population, and the advent of cell phone cameras. In addition, the science is unclear on if climate change has impacted, or may impact, tornado frequency or intensity overall or in certain circumstances. Congress may consider whether—and, if so, how—federal agencies should research potential connections between climate change and tornado activity.

Eva Lipiec, Specialist in Natural Resource Policy

IF12695

Tornadoes: Background and Forecasting

https://crsreports.congress.gov | IF12695 · VERSION 3 · UPDATED

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