Thursday, July 31, 2008
As we wait and wish for showers and thunderstorms, parts of the country are getting rocked with severe weather today. A classic wind storm across the upper Midwest known as a Derecho is causing a great deal of problems for our friends to the north causing numerous wind reports in excess of 80mph and very large hail, up to baseball size, have been reported. Below is a short radar clip of the Derecho as it moves into Western Minnesota.
Many times Derechos develop form a single Supercell thunderstorm that becomes outflow dominate, undercutting the updraft needed to sustain the Supercell. Along this outflow boundary, new storms fire and continue to grow in strength. As the system grows, the speed it travels increases and widespread wind damage can occur. Winds as high as 100mph to 120mph can occur along a Derecho causing tornado like damage. In many cases, the Derecho is worse than many small tornadoes as much of a Derecho’s wind can be in the EF-2 tornado range. Imagine a swath 50 to 100 miles wide of EF-2 tornado like winds. Damage can be tremendous. Also, many times on the north end of the Derecho, a rotating comma head can form producing small tornadoes. In the clip above you can make out a rotating comma head. There were numerous tornado warnings along this line in the area of that comma head. An event very similar to this occurred earlier this year with an EF-1 tornado in Kilgore and Longview. A bow echo moved through with a rotating comma head producing a 21 mile long path of EF-0 and EF-1 tornado damage. There have been many Derecho events across the Southern Plains. For more information on historic Derecho events click the link below.