21 WFOs have the opportunity to participate in a pre-operational Geostationary Lightning Mapper (GLM) evaluation starting late June 2018. Forecasters in the test offices are evaluating experiential GLM total lightning products in real-time in AWIPS-II. The initial products include Flash Extent Density (FED), Total Optical Energy (TOE), and Average Flash Area (AFA). The products are available as a 1-minute accumulation updating every 1-minute, and a 5-minute accumulation updating every 1-minute. The GLM data are re-navigated to the 2×2 km ABI fixed grid. These products were initially tested in the Hazardous Weather Testbed (HWT) and Operations Proving Ground (OPG) during this past spring. Visit the GOES-R HWT Blog for feedback from the HWT evaluation. The examples below are using 1-min updating 5-min accumulation GLM data with 1-min visible ABI imagery on 13 July 2018 from 2000 UTC to 2059 UTC for a strong thunderstorm in northern Iowa.

Flash Extent Density (FED): FED has been tested in NOAA testbeds and offices for several years leading up to the launch of GOES-R using proxy ground-based lightning data. It has been found to be a useful means of displaying gridded lightning data. This product represents the number of flashes that occur within a grid cell during the period of time (Fig 1). Rapid increases in this product indicate increasing updraft intensity and potential severe threat while decreases in FED would indicate weakening updraft.

Figure 1: 13 July 2018 GOES-16 1-min, 5-min accumulation GLM FED and 1-min ABI visible imagery. Full res

Total Optical Energy (TOE): Sum of all optical energy observed within each grid cell during the period. This is the closest portrayal to what GLM is actually sensing (Fig 2).

Figure 2: 13 July 2018 GOES-16 1-min, 5-min accumulation GLM TOE and 1-min ABI visible imagery. Full res

Average Flash Area (AFA): Average area of all flashes spatially coincident with each 2×2 km grid cell during the period (Fig 3). Smaller flashes indicate newer flashes, and are typical of the core updraft region. Longer flashes are typical in the anvil away from the updraft core, and highlight storms that are capable of producing strikes far from the updraft core.

Figure 3: 13 July 2018 GOES-16 1-min, 5-min accumulation GLM AFA and 1-min ABI visible imagery. Full res

GLM has an advantage over ground-based lightning networks in that it detects the extent of lightning flashes instead of a single point, and has uniform detection efficiency across a large domain. Ground-based networks are able to differentiate cloud-to-ground and in-cloud lightning flashes. Therefore, a forecaster gets the greatest benefit when using GLM in tandem with ground-based lightning data.

The figure 4 4-panel includes all three GLM lightning products plus NLDN point CG lightning data and ABI visible imagery. Notice the long flashes extending well into the anvil northwest of the core updraft region. NLDN CG strikes are detected in this region. Meanwhile within the updraft, AFA is much smaller.

Figure 4: 13 July 2018 GOES-16 1-min, 5-min accumulation GLM FED (top left), AFA (top right), TOE (bottom right), ABI VIS and NLDN CG (bottom left). Full res

The thunderstorm produced a 49 mph wind gust around 2040 UTC, during the time of peak FED just before a decrease in FED and storm intesity.

In addition to providing forecasters with information about fluctuations in storm intensity, the GLM data will be utilized for alerting the public at outdoor events when lightning threatens.

Bill Line, NWS