[20220503]IN11826_龙卷风：背景和预测.pdf

CRS INSIGHT Prepared for Members and Committees of Congress INSIGHTINSIGHTi i Tornadoes: Background and Forecasting Updated May 3, 2022 Background Severe thunderstorms and tornadoes affect communities across the United States every year, causing fatalities, destroying property and crops, and disrupting businesses. Tornadoes are narrow, violently rotating columns of air that extend from the base of a thunderstorm to the ground, sometimes producing winds that exceed 300 miles per hour. Tornadoes have been reported on all continents except Antarctica; however, 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, shifting seasonally: (1) southern Plains (e.g., Texas, Oklahoma, Kansas), (2) Gulf Coast, 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. For example, a deadly storm system with several reported tornadoes touched gr