Lightning in the Tennessee Valley

If April showers bring May flowers, then what do May showers bring?  So far, they bring the Huntsville Airport to 5.84″ above the entire normal May accumulation of rainfall, with 6.32″ reported through May 3rd.  Numerous severe weather reports occurred across the Southeast, with isolated reports of severe wind and tornadoes in Northern Alabama.  The Tennessee Valley benefits from an additional remote sensing tool: the North Alabama Lightning Mapping Array, which is capable of tracking sources of lightning within clouds, identifying their likely altitudes, and reports data beyond the cloud-to-ground data commonly used for television broadcasts and Internet sources.  SPoRT/NASA MSFC provides lightning source products to forecast offices within the region, which can provide additional information regarding the development or decay of thunderstorms.  Daily composites from the weekend’s events highlight characteristics of recent events.

Lightning sources accumulated from 00 to 2359 UTC on 1 May 2009, as sampled by the North Alabama Lightning Mapping Array.

Thunderstorms on 1 May 2009 were tracking eastward across Tennessee, eventually forming into a convective line that draped southwestward and into Northern Alabama.  This contributed to a round of heavy thunderstorms and precipitation during the evening rush, along with some minor urban flooding.  Lightning occurred frequently within the Huntsville, Alabama county warning area.

As in the figure above, but for the 2 May 2009 period.

On Saturday, convective activity generally migrated eastward from Mississippi and Arkansas.  The generally eastward migration of the activity limited the number of lightning returns deep into Tennessee, while individual “streaks” of enhanced lightning returns can be observed in far western Alabama, likely associated with isolated or embedded supercells that contributed to reports of isolated, short-lived tornadoes and wind damage.

Finally, the severe weather event wrapped up late Sunday afternoon.  Here, the LMA depicts blatant streaks of lightning sources that moved northeast in association with tornadic supercells in the Birmingham area.  Although this is a composite of sources throughout the day and cannot be used to investigate a single storm, it is interesting to note isolated enhancements in LMA returns along some of these streaks.  Rapid changes in the production or cessation of lightning have been proposed as indicators for a strengthening or decaying thunderstorm, based on changes in the amount of precipitation ice and vertical flux by updrafts and downdrafts.  These are current areas of research by faculty, staff and graduate students at the University of Alabama in Huntsville (UAH).  SPoRT partners with UAH and the local National Weather Service Forecast Office to evaluate the operational value of lightning data, and is currently exploring methods for visualizing and applying these tools within the Advanced Weather Information Processing System, Version 2 (AWIPS 2) that will be deployed in the upcoming year.

As in the above figures, but for the 3 May 2009 period.

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