Total Lightning and IDSS in Stratiform Precipitation

A methane explosion occurred last Friday, January 20, in rural northwest Alabama (story from WAFF-TV).  NWS Huntsville provided decision support services to the incident, which posed significant risks to emergency personnel.  The active pattern last weekend created additional concerns, since several rounds of rain and thunderstorms were forecast to move across the area (though fortunately the significant severe weather from that weekend remained well to the south).

One such event arrived Saturday morning as stratiform rain pushed back into the area. Forecasters noted that there were indications of cloud-to-ground lightning from the National Lightning Detection Network along the leading edge of the rainfall, so we leveraged flash extent density data from the North Alabama Lightning Mapping Array to investigate further.  Strangely, when loaded as an image in AWIPS-2, this showed little.

It took some time to discover why.  The flash rates were so low (1 flash per ‘scan’) that the FED image interpolation was smoothing the data below what the color curve could visualize.  After the interpolation was turned off or the color curve edited again, the flashes were much more apparent, as seen in the following GIF loop from AWIPS.

methaneexplosion

A loop of Multi-Radar/Multi-Sensor radar imagery from 1144 UTC to 1222 UTC, 21 January 2017, with flash extent density data from the North Alabama Lightning Mapping Array overlaid in white.  The methane incident is denoted by the yellow dot in northwest Alabama, and a 10-mile range ring is indicated by the yellow circle.

Adding the full flash extent density information from the NALMA helped the forecasters to visualize the lightning threat beyond what was otherwise available in AWIPS.  This helped when it came time to brief emergency personnel on the approaching threat.

This event also helps to reinforce the potential utility of the Geostationary Lightning Mapper (GLM) aboard GOES-16 as it becomes available this spring.  However, forecasters will have to visualize the GLM data wisely.  It will likely more important to view low flash rates for an IDSS or safety mindset, versus higher flash rate changes for severe weather.  Even with total lightning, context is everything.

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