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1 1 (June 26, 2024)

handle is hein.crs/govephr0001 and id is 1 raw text is: Tornadoes: Background and Forecasting June 26, 2024 Tornadoes are narrow, violently rotating columns of air, extending from the base of a thunderstorm to the ground, that affect communities across the United States every year. Tornadoes can cause fatalities and injuries, destroy property and crops, and disrupt businesses. For example, a weather system on April 26-28, 2024, produced over 200 tornadoes, high winds, and large hail and caused multiple deaths and injuries across the Midwest and South, according to preliminary estimates. Tornadoes have been reported on all continents except Antarctica. They occur most commonly in North America, particularly in the United States, which reports approximately 1,200 tornadoes per year. Tornadoes occur across the United States but form frequently in three regions: (1) southern plains (e.g., Texas, Oklahoma, Kansas), (2) Gulf Coast (e.g., Alabama, Florida, Louisiana, Mississippi), and (3) northern plains and upper Midwest (e.g., North and South Dakota, Nebraska, Iowa, Minnesota). Tornadoes occur mostly during spring and summer (Figure 1) and usually during the late afternoon or early evening. However, tornadoes can occur at any time. 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, called the enhanced F- scale, or EF-scale (Table 1). The EF-scale uses 28 different types of damage indicators, such as building type, structures, and trees. Table I. Enhanced F-Scale EF Number 3-Second Gust (mph) 0 65-85 I 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 I. U.S. Tornadoes Daily Count and Running Annual Trend C C U 0 C 0 U C C 4 jaw 4et~ Mau ~Apr~~May- Jun- -Jub -Aup~Se~-Oct ~Nov- 4)ec #PwIumnary tornadoes 1mm NW$ Local Storm Reports (LSfASj Daiv and annual averaaes are based on or&iminarv LSR& 2005 2015 Source: NOAA, Storm Prediction Center, Daily Counts and Annual Running Trend, June 23, 2024. Notes: The 2024 U.S. daily occurrence and trend for tornadoes is shown in red, and the average daily and annual trend (2005-2015) is shown in gray.

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