One year ago today, one of the most incredible tornado outbreaks in our nation’s history was beginning to unfold. On April 25, 2011, portions of Texas, Arkansas, Louisiana, Mississippi, Tennessee, Missouri, and Kentucky were hit with the first round of a multi-day tornado outbreak. The outbreak would reach its peak on April 27, 2011, a day which still resonates across the NWS Huntsville county warning area.
Last year, after the worst of the impacts had died down, we posted some quick analysis of MODIS satellite imagery showing the tornado scars. That post turned into a full page of analysis on the SPoRT website (including higher-resolution data from the ASTER instrument), a presentation at the National Weather Association meeting in Birmingham, and an article in AGU’s Eos publication.
With the anniversary of the event coming Friday, I wanted to take a look at MODIS imagery to see how the satellite perspective has changed. Much of the damage has been cleaned up on the ground, but the tree damage–which is the most obvious change to reflectance that the MODIS instrument detects–will remain for a long time to come. And indeed, MODIS can still pick up on many of the same tornado tracks from last year, without any augmentation, and straight out of AWIPS.
The first image is the 250-meter visible image, which last year yielded some of the most useful information in terms of path length, path width, and overall visibility. Some of the paths are a bit harder to see one year later, but many are still obvious in comparison to the surrounding landscape.
Due to the early “green-up” this spring–and the subsequent lack of vegetation in the tornado paths–the 500-meter color composite is arguably more telling. The paths appear narrower (and a bit harder to find) due to the lower resolution of the color composite imagery, but the paths stand out sharply in forested areas. Much like last year, the tornado paths that cross farmland, such as the Hackleburg-Harvest EF-5 (the northern-most track on the map), fade out as they approach areas where vegetation is more sparse. In these areas, there is less vegetation to disturb, and less of a change in reflectance to detect via satellite.
Past research has suggested that these storm damage scars will persist on satellite imagery for years to come, so we will continue to monitor MODIS over the coming years to comfirm that. Much like the mental and emotional scars, these physical scars will take a long time to heal.