![]() High resolution multispectral and temporal composites helped forecasters corroborate their damage assessments, determine starting and ending points for tornado touchdowns, and helped to provide forecasters with a better big-picture view of the damage region. Satellite data from NASA's MODIS and ASTER instruments played a helpful role in determining the location of tornado damage paths and in the assessment. Survey activities included site visits to the affected locations, analysis of radar and satellite data, aerial surveys, and interviews with eyewitnesses. Meteorologists from the the NWS performed extensive surveys to assess the intensity, duration, and ground track of tornadoes reported during the event. The use of Doppler radars covering the region provided reflectivity and velocity signatures that allowed forecasters to monitors the severe storms from beginning to end issuing hundreds of severe weather warnings throughout the day. In Alabama alone, there were 61 confirmed tornados, 4 of them produced EF5 damage, and several were on the ground an hour or more with continuous damage tracks exceeding 80km. Numerous tornadoes caused extensive damage, and tragically, the deaths of over 300 people. During severe weather situations, reflectivity signatures can provide valuable clues as to what threats to expect from a particular cell.Coupling Between Doppler Radar Signatures and Tornado Damage Tracks On April 27, 2011, the southeastern United States was raked with several episodes of severe weather.Bright reflectivity returns that are stationary and appear during both calm and inclement weather are usually land-based obstructions such as mountains, trees, or especially wind farms (nothing gets electromagnetic signals confused like spinning metal blades!). ![]() ![]() This is helpful for picking out snow/mix/rain transition zones In all snow situations, dBZ values of 40 indicate 3-4”/hr snowfall rates and whiteout conditions. Anything larger than this is usually due to “bright banding” where the radar is seeing the part of the atmosphere where snowflakes are clumping together and melting into raindrops.
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