Meteorology: Understanding the Atmosphere Ackerman and Knox
08 August 2001 - Thunderstorm Downburst Wind Event Over North Dakota and Minnesota
NOAA GOES-8 visible and 10.7 micrometer InfraRed (IR) channel imagery (above) shows the development of severe convection that produced tornadoes, large hail and damaging winds across parts of North Dakota and Minnesota during the afternoon and evening of 08 August 2001. Thunderstorm downburst winds gusted to 114 mph at Grand Forks Air Force Base ND (station identifier KRDR) at 01:16 UTC (8:16 PM Central time), 101 mph at the Grand Forks ND National Weather Service office (near KGFK) at 01:26 UTC (8:26 PM Central time), and 79 mph at 01:56 UTC (8:56 PM Central time) at Crookston MN (KCKN). Well-defined overshooting tops were evident on the visible imagery, and IR imagery indicated cloud top temperatures as cold at -68 C (dark red enhancement) to the northwest of Grand Forks just prior to the damaging winds at the surface. Less than 24 hours earlier, other thunderstorms had produced winds gusting to 110 mph at Hillsboro ND, just 35 miles south-southeast of Grand Forks. Notice how the surface temperature, dew-point, and wind speed and direction change as the storm passes over a weather station.
Grand Forks WSR-88D radar base velocity data showed inbound velocities of 50-64 knots as the storm was approaching Grand Forks at 01:04 UTC (above), and outbound velocities of 50-64 knots as the storm was passing Crookston MN at 02:00 UTC (above, right). Radar base reflectivity data also revealed a west-east oriented boundary (19:24 UTC | 21:33 UTC | 23:37 UTC | - Java animation -) moving southward through the Grafton region toward Grand Forks as the convection was approaching from the west. This boundary may have played a role in the intensification and motion of the convection as it moved through northeastern North Dakota and northwestern Minnesota.