This particular blog post focuses on total lightning observations from the Moore, Oklahoma tornado. SPoRT is participating in the annual NOAA Hazardous Weather Testbed Spring Experiment in Norman, Oklahoma. The Spring Experiment is demonstrating new NOAA and NASA experimental capabilities as part of the annual Experimental Warning Program. One NASA capability being demonstrated is total lightning associated with severe / tornado weather events. The data used were NOT from NASA, but from the Oklahoma Lightning Mapping Array operated by the University of Oklahoma. NASA SPoRT has access to these data through a collaboration to support the Hazardous Weather Testbed and demonstrates SPoRT’s software plug-in to display these data in the National Weather Service’s AWIPS II system. Also, this collaboration is demonstrating the SPoRT / MDL total lightning tracking tool. This particular post discusses the connection of total lightning and tornado occurrence consistent with the “lightning jump” concept developed by Christopher Schultz (NASA Coop) and the lightning team here at the Earth Science Office. These experimental data were not available to the Norman, Oklahoma forecast office and this post is intended as a discussion of how these data may have been used.
Figure 1 takes place at 1910 UTC and shows a 4-panel display from AWIPS II. The lower two panels show radar observations of storm relative velocity (left) and reflectivity (right). The top panels show two total lightning products. The first is the source density product (left), which is used by several SPoRT partners in operations. The pseudo-geostationary lightning mapper (PGLM – right) is the demonstration product SPoRT is providing to the Hazardous Weather Testbed this year to demonstrate what the future Geostationary Lightning Mapper observations may look like. The PGLM data are derived from the ground-based lightning mapping array data. In this case it is from the Oklahoma network provided to SPoRT with this collaboration. Lastly, please note the two pop-up windows. These display the output from the SPoRT / MDL total lightning tracking tool, which is a time series of the source densities (left) and PGLM (right) observations, respectively. Newcastle and Moore, Oklahoma are circled for reference.
Figure 1: AWIPS II four panel display from 1910 UTC that shows the total lightning source density (upper left), and pseudo geostationary lightning mapper flash extent density (PGLM – upper right), along with the radar storm relative velocity (lower left), and radar reflectivity (lower right). The pop-up windows show the total lightning tracking tool’s time series plot for the source densities (left) and PGLM flash extent density (right), respectively.
Both the source density and PGLM demonstrate a lightning jump around 1910 UTC, as shown by the spike in observations in the time series (~800 sources and 46 flashes, respectively). Christopher Schultz’s official lighting jump algorithm supports this visual inspection as it too indicated a lightning jump. Interestingly, the first severe thunderstorm warning was issued at 1912 UTC and based on radar observations at 1908 UTC. Normally, we train that lightning jumps will precede severe weather, so why is the jump coincident with the initial severe thunderstorm warning? The answer is that the environment in central Oklahoma was extremely favorable for tornadic supercells. As such, as storms showed any signs of growth a warning was issued. This is similar to how the Huntsville forecast office operated during the April 27, 2011 outbreak as there were so many violent storms across the region. Given the environment, the total lightning would play a reinforcing role as the lightning jump at 1910 UTC indicates that this storm is rapidly strengthening and becomes rooted in the boundary layer. One feature that the total lightning observations provide is a very rapid update cycle. The total lightning data update every minute, versus the radar updating every 4-6 minutes. This means that the total lightning observations are providing continuous updates into how the storm is evolving, allowing the forecaster to evaluate the storm’s growth in between radar volume scans.
We will next step forward to 1928 UTC, shown in Figure 2.
Figure 2: This is the same as Figure 1, but at 1928 UTC.
The total lightning observations begin to undergo a second, reinforcing lightning jump at 1928 UTC. The time series plot is less obvious than from 1910 UTC, particularly with the source densities, but the lightning jump algorithm did flag a reinforcing jump at this time. At this point, this is 12 minutes before the official tornado warning at 1940 UTC and 28 minutes prior to the reported touchdown time of 1956 UTC, near Newcastle, Oklahoma. This reinforcing jump emphasizes to the forecaster that something is occurring and that the storm continues to intensify. Given that a severe thunderstorm warning is already active, this reinforcing jump alerts the forecaster that this storm is unlikely to weaken soon. The radar reflectivity emphasizes this as well, as it begins to take on a supercell structure and a faint hook echo may be forming (circled in reflectivity frame).
Figure 3 comes at 1940 UTC, shown in Figure 3, when the tornado warning was issued.
Figure 3: This is the same as Figure 1, but at 1940 UTC.
At this stage, the lightning activity has decreased somewhat after the initial jump at 1910 UTC and the reinforcing jump at 1928 UTC. Radar continues to show intensification, particularly with the radar velocity couplet clearly evident to the west-southwest of Newcastle, Oklahoma.
We will next step ahead to 1950 UTC, just prior to the touchdown of the tornado at 1956 UTC in Figure 4.
Figure 4: This is the same as Figure 1, but at 1950 UTC.
At this stage, the tornado warning has been active for 10 minutes and the radar observations show the classic hook echo and velocity couplet signatures. Both total lightning products show one final increase in activity, but given the high values for the past few minutes, this is not a third lightning jump. The tornado would touchdown 6 minutes later just outside of Newcastle, Oklahoma before further intensifying and moving through Moore, Oklahoma.
Christopher Schultz provided an additional radar analysis that is a cross section of the radar azimuthal shear (a measure of the storm’s rotation) in time in Figure 5. Red vertical bars show the occurrence of the original and reinforcing lightning jump at 1910 and 1928 UTC, respectively. Of note is the large increase in azimuthal shear after each lightning jump prior to the tornado’s touchdown.
Figure 5: A radar azimuthal shear cross section plot from 1900-2300 UTC. The red bars indicate the times of lightning jumps from the lightning jump algorithm.
Once again, I would like to re-iterate that these experimental data were not available to the forecasters in real-time and that this is a post-event analysis. Overall, the total lightning data behaved as expected, with two lightning jumps preceding the severe weather and the tornado that would later impact Moore, Oklahoma. Based on the extremely favorable environment for tornadic supercells, the total lightning data would play a supporting role providing insight into the storm’s development for a forecaster, particularly with its one minute update times. Total lightning typically has more utility in marginal events, but the post-analysis here shows that the underlying concepts of what drives a lightning jump are just as valid here.