Monday, 23 January 2017
4E (Washington State Convention Center )
A severe weather outbreak occurred along a line of discrete supercells on 26-27 August 2007 over the Northern Great Plains region of the United States and also affected the Canadian provinces of Manitoba and Ontario. There were numerous reports of large hail (>25 mm) and a few violent tornadoes (EF3+) including the devastating EF4 tornado that struck Northwood, North Dakota. An increase in cloud-to-ground (CG) lightning activity (e.g., lightning jump) along the line was observed by the National Lightning Detection Network (NLDN) just before the violent tornado was reported (0145 UTC 27 August 2007). Interestingly, nearly all supercells appeared to experience this jump at the height of the convective event (0135-0150 UTC 27 August 2007) and just over 50% of the lightning strikes were identified as positive by the NLDN. The Northwood tornadic supercell accounted for 23% of the lightning activity in which 25% of the lightning strikes were identified as positive, and 37% of the positive strikes had peak currents exceeding 100 kA. Furthermore, two supercells in Canada had positive lightning strikes that accounted for over 80% of the total number of lightning strikes at the peak of their duration. This study examines seven supercells within the line of storms in terms of dynamic/thermodynamic environment, a detailed analysis of the lightning behavior, and cloud microphysical properties (e.g., aerosols, cloud liquid and ice water contents (LWC and IWC)). Note that the storms initiated under strongly polluted conditions as biomass burning smoke from wildfire activity originating from the intermountain west was observed in the region prior to initiation.
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