Graphical plots of lightning trends

In our evaluation of the 24 May 2008 archive case today, forecasters highly recommended implementation of a gridded map display of lightning trends in addition to counts. The idea is as follows:

Need to have trend plots, because it's too hard to figure out by querying flash count grids. The forecasters preferred a gridded plan view / map mode (not a line graph), and either a plot of (1) the flash rate derivative or, in the lightning jump sense, (2) the number of standard deviations (possibly fractional, e.g., 1.5) relative to the running mean. This could be implemented using the WDSSII k-means cell shape colored according to the above trend metrics. 30 min time lapse trend swath would also be helpful.

Work by Schultz et al (2009) has shown the applicability of a two-standard-deviation jump of the flash rate derivative above a running mean as predicator of hail, wind, and tornado events. About a year ago, I prototyped a visualization of a cell-entity plot that could graphically show how close the current flash rate was to being considered a lightning jump. These data are courtesy Chris Schultz, for a case from July 16, 2007.

In the video below, the top two panels show time versus (top) flash rate) and (bottom) the flash rate derivative with respect to time (DFRDT), and various threshold- and standard deviation-based thresholds for lightning jump. The bottom panel shows a plan view of a thunderstorm cell colored according to the ratio of DFRDT to the 2-sigma trigger (thick blue line vs. pink line). Yellow colors show that the cell is fliriting with jumping, and the discontinuity to red in the color scale at a ratio above 1.0 calls attention to the jump without requiring an additional symbolic flag.



A real storm cell derived from the WDSSII k-means tracking approach would have a non-circular entity shape, which would obviously be much more realistic than the simplistic circle used here. This demo doesn't show the swath idea, but it is clear that it could definitely improve awareness of flash rate trend history at a glance.

Also, a forecaster just suggested to me that a plot of IC:CG ratio would be interesting, perhaps implemented on a cell basis like the trend plot discussed above. He noted interest in continued availability of the NLDN ground strike (and polarity) data.


Reference:
Schultz, C. J., W. A. Petersen, and L. D. Carey, 2009: Preliminary development and evaluation of lightning jump algorithms for the real-time detection of severe weather. J. Appl. Meteor. Climatol., 48, 2543–2563.