GLM & Public Safety: An Important Caveat

As great as is to use data from the Geostationary Lightning Mapper, there is an important caveat forecasters have to consider when using the data.

During the afternoon of July 11, typical “air mass” showers and thunderstorms were developing across northern Alabama, including several south of the Huntsville International Airport.  At 12:18 PM CDT, the GLM Flash Extent Density data started to light up with these cells, including one larger flash at 12:21 PM.  (Huntsville airport is marked by the eastern concentric yellow circles.)

KHTX radar valid 1722 UTC 11 July 2018 and GLM FED valid 1721 UTC

As I’ve noted before, we issue airport weather warnings for Huntsville if lightning is within 5-10 miles, heading towards the terminal.  So forecasters were justifiably alarmed that GLM flashes were starting to show up within the 10-mile range ring, and just barely edging towards the 5-mile ring.

But here is where that caveat comes into play: the parallax effect.  Radar showed the actual echoes associated with these flashes to be well to the south of the GLM flashes.  Earth Networks Total Lightning data from the same time period showed lightning confined to these cells well outside the 10-mile range ring.  Furthermore, the cells were moving away from the field.

KHTX radar valid 1722 UTC 11 July 2018 and Earth Networks total lightning valid 1721 UTC

KHTX radar valid 1722 UTC 11 July 2018 and Earth Networks total lightning valid 1721 UTC

It’s worth noting that GLM showed a greater spatial extent during some of these flashes, but Earth Networks was much closer in location to the radar.

So while a cursory glance at the GLM data might lead to an airport weather warning, it was important to double-check GLM against the radar–and recognize that an AWW was not necessary in this case.  The same caution will need to apply as we begin applying GLM to other public safety situations.

GLM Detection of Anvil Lightning

During the evening hours of June 27th, we noticed that GLM average flash area data was indicating a substantial flash from the main core of storms over northeast AL/northwest GA towards middle TN.  This occurred around June 28th, 0130Z-0140Z, and I have included both a screen shot and animation for this flash.  Though no DSS events were scheduled over this particular area, it would be of great benefit to utilize this for potential lightning impacts at outdoor events–where lightning is occurring well away from the storm core/updraft. Also of note was the GLM flash extent density showing a noticeable jump throughout the evening with the stronger updrafts. This aided in the decision to keep a significant weather advisory in place for these storms.

For purposes of calibration and given my experience with utilizing GLM data at a recent HWT (May), I prefer having a four panel display in D2D. ENTLN data overlaid on Flash Extent Density while the other available parameters (Average Flash Area and Total Optical Energy) are on two other panels.

GLM_062818_0130Z_LightningFlashAnvil-AnnotatedFigure 1: Four panel of GLM data with MRMS Composite reflectivity in bottom left, annotated Average Flash area in bottom right, flash extent density with overlaid ENTLN data in top left, and Total Optical Energy in top right.


GLM_062818_0130Z_LightningFlashAnvil_AnimationFigure 2: Same as in Figure 1, just animated.

The nice thing is that there were generally no latency issues noted other than intermittent 2-3 minute delays to real time.

-Stephen Latimer (NWS Huntsville)


Using GLM for Airport Weather Warnings

As part of our impact weather responsibilities, NWS Huntsville issues Airport Weather Warnings (AWWs) for Huntsville International Airport (KHSV) and Northwest Alabama Regional Airport (Muscle Shoals; KMSL).  AWWs are issued for the threat to personnel working outside at the terminal and neighboring operations, not for the threat to aviation as a whole.  One of our criteria for AWW issuance is the threat of cloud-to-ground lightning within 5 miles.

On May 30, a relatively small line of thunderstorms developed over northeast Mississippi and tracked to the east, producing a few pockets of straight-line wind damage along the way.  The line approached the 10-nm range of KHSV at 2320 UTC (seen below).  At this point, GLM Flash Extent Density (FED) data wasn’t the most helpful data set for deciding to issue an AWW; the National Lightning Detection Network (NLDN) was already detecting a great deal of cloud-to-ground lightning with the storms.


Multi-Radar/Multi-Sensor (MRMS) Reflectivity At Lowest Altitude (RALA) valid 2320 UTC 30 May; 5-minute NLDN flashes valid 2321 UTC; and GLM Flash Extent Density valid 2321 UTC.  The 5 and 10-nautical mile range rings around KHSV are illustrated in coral near the center of the image.

The GLM FED data were far more useful later on in the event, after the line passed well east of KHSV and the Huntsville metro area.  With nightfall, the convective updrafts weakened and lightning along the line generally decreased–but flashes within the trailing stratiform region of the quasi-linear convective system (QLCS) did not.  One of the more spectacular examples occurred around 0059 UTC (seen below).  The FED product really illustrated the spatial threat simply and effectively, especially when combined with the NLDN data.  (This example uses a slightly different color curve from the GLM baseline to enhance lower flash rates.)


MRMS RALA valid 0058 UTC 31 May; 5-minute NLDN valid 0059 UTC; and GLM FED valid 0059 UTC.  5 and 10-nm range rings around KHSV are also noted.

GLM helped forecasters acquire and retain situational awareness of these trailing stratiform “long flashes”, which helped with AWW extension/reissuance.  As a result, the airport weather warning for Huntsville was re-issued until the trailing stratiform region cleared the airport and the threat subsided.

Geostationary Lightning Mapper detects lightning in the Volcanic Plume from the Fuego Volcano in Guatemala (3 June 2018)

During the eruption of the Fuego Volcano on the afternoon of Sunday June 3, 2018, the Geostationary Lightning Mapper observed a rare, but important, phenomenon: volcanic lightning.  A total of five lightning flashes were observed between 1814 and 1834 UTC with the rising plume.  The first three flashes between 1814 and 1818 UTC were 8 to 10 km north-northeast of the volcano. Then as the plume continued to advect to the northeast of the volcano, the position of the lightning followed. A flash at 1822 UTC was 13 km from the cone of the volcano, and the flash at 1833 UTC was farthest away from the cone of the volcano at 15 km.

Animation of GLM group densities from 1810 to 1835 UTC on 3 June 2018. The location of the volcano is circled.

One of the unique features of GLM is the ability to measure the size of the flash directly as each flash is observed.  In thunderstorms, flash size is a good indicator of vertical motion, which is often hard to directly measure within thunderstorms, or in this case, a volcanic plume.  Between 1814 and 1822 UTC, flashes were occurring approximately every 2 to 4 minutes, and their size was on the order of 500-1000 km2.  Then between 1822 and 1834 UTC there was a lull in GLM-detected lightning activity, followed by the largest flash detected by GLM during the event at 1500 km2 as the plume continued to expand over central Guatemala.

There was a 3 hour lull in GLM-detected activity, until 2141 UTC, when a second set of 21 flashes was detected by GLM between 2141 and 2203 UTC. These flashes were located between 1 and 8 km south-southeast from the highest point of the volcano and correspond in time and reported location of the deadly lahar and pyroclastic flow that came down the south side of the volcano. GLM flash sizes ranged from 64 km2 up to 1500 km2 and there was not as clear of an increase in size as observed with the volcanic plume.

Animation of GLM group densities from 2139 to 2205 UTC on 3 June 2018. The location of the volcano is circled.

Operational Utility of GLM Flash Extent Density on June 1

For the seventh consecutive year, NWS Huntsville provided on-site weather support for a large outdoor country music concert in Cullman, Alabama this past weekend. This concert is usually held in June, one of the most problematic times of year for forecasting due to the seemingly-random nature of summertime convection. Public safety officials have had to stop the concert once for the threat of cloud-to-ground lightning and gusty winds, and have come close on several other occasions.

This year’s event was no exception. On Friday night, June 1, a small multi-cell cluster of storms containing cloud-to-ground lightning developed approximately 30 miles to the west and moved steadily east, putting forecasters and public safety officials alike on alert.

In past years, NWS Huntsville forecasters have used the North Alabama Lightning Mapping Array for situational awareness. Unfortunately, the NALMA is no longer available, but NWS Huntsville is a Preliminary Test & Evaluation site for the GOES-16 Geostationary Lightning Mapper (GLM). So forecasters at both the NWS office and the concert used GLM to evaluate the threat to almost 30,000 people.

Four Panel image of GOES-16 Clean IR (top-left), MRMS radar reflectivity (top-right), Earth Networks 8-km total flash density (bottom-right), and GLM FED and NLDN plot (bottom-left), vallid 0113 UTC 1 June.  The concert is denoted by the crosshairs marked “Home”.

Fortunately, the initial cluster of storms to the west essentially “split”, with one updraft gaining dominance to the south, and the rest weakening.  There were some “long flashes” extending far to the north from the southern storm, and far to the south from the northern storm, as seen in the image above.

The storm to the south produced a great deal of lightning, but thanks to the GLM Flash Extent Density product, forecasters were able to determine that the concert would not be affected.

As the storm to the south was weakening, the northern storm regained strength and intensified.  GLM FED data shows several flashes moving into the 10 nautical mile range ring, and one moving within the 5-nm ring.  Public safety officials and forecasters were certainly concerned.  However, forecasters were able to combine GLM FED information with GOES-16 IR and Multi-Radar/Multi-Sensor radar data to determine that the storm was moving away, the updraft was intensifying (which typically leads to smaller flashes), and the lightning threat would gradually diminish.

Four Panel image of GOES-16 Clean IR (top-left), MRMS radar reflectivity (top-right), Earth Networks 8-km total flash density (bottom-right), and GLM FED and NLDN plot (bottom-left), vallid 0151 UTC 1 June.  The concert is denoted by the crosshairs marked “Home”.

The northern storm would eventually produce quite a light show for skywatchers in the Huntsville metro area–but it also did much more.  Later on, GLM FED data indicated a lightning increase at 0207 UTC, followed by a more pronounced increase at 0216 UTC.

Animation 0156-0259 UTC of GOES-16 Clean IR 1-minute imagery (top-left), MRMS radar reflectivity (top-right), Earth Networks 8-km Total Flash Density (bottom-right), GLM FED and NLDN plot (bottom-left)

Indeed, this storm eventually downed numerous trees along the Madison-Marshall county line around 0240-0250 UTC.

With our legacy of using LMA data for almost 15 years, NWS Huntsville forecasters have embraced GLM FED data eagerly.  We hope to share more operational examples in the future.

Wet streaks in soil moisture observed in west Texas…

This morning I observed some rather odd looking streaks in the 10.3 µm imagery in western portions of Texas.  Sampling the 10.3 µm data revealed alternating areas of relative warm/cool skin surface temperatures in the cloud free conditions in the area on the upstream side of departing deep convection.  The temperature difference in the skin temperatures were around 5 C at this time.  The 10.3 µm image below was taken from appox. 1357 UTC this morning (3 May 2018).

Image 1.  10.3 um imagery from GOES-16, 1357 UTC 3 May 2018

Arguably, the streaks of lower temperature values showed up better in the 3.9 µm imagery.  Notice the streaks or alternating bands of yellow/orange colors in portions of west Texas.

Image 2.  3.9 um imagery from GOES-16, 1357 UTC 3 May 2018

Realizing these temperature differences were likely due to the recent convective rainfall, I looked up the SPoRT LIS 0-10 cm volumetric soil moisture data, which corresponded nearly perfectly with the streaks of relative lower temperature values (Image 3).  So indeed, this was due to the recent heavy, convective rainfall across the area.

Image 3.  SPoRT LIS 0-10 cm Volumetric Soil Moisture, 15 UTC 3 May 2018


Extreme Wildfire Setup over Southern High Plains for 17 April

The fire weather outlook for today (17 April 2018) looks very dire over the Southern High Plains of western Texas, New Mexico, and portions of western Oklahoma, southwestern Kansas, and southeastern Colorado. The combination of very little precipitation in recent months along with expected strong winds and extremely low relative humidities will set the stage for potentially dangerous wildfires over this region. The NCEP Storm Prediction Center has the highest threat category in today’s fire weather outlook across the region, with a large swath of extremely critical fire weather conditions expected (Fig. 1).

The persistent lack of precipitation over the Southern High Plains and Desert Southwest regions and its impact on deep-layer soil moisture is captured by the SPoRT-LIS 6-month change in total column relative soil moisture, as posted on the SPoRT-LIS graphics web page (Fig. 2;  A sharp transition lies across Kansas, Oklahoma and Texas, where a strong drying signal is seen across western portions of these states into New Mexico, Arizona, and Mexico, whereas dramatic moistening is prevalent in the last 6 months over the Mississippi, Ohio, and Tennessee River Valleys.  Substantial drying is also noted over the southern Florida Peninsula, with wetting seen over the West Coast and Pacific Northwest (Fig. 2).

Since the unusual and persistent dry pattern over the Southern Plains and Desert Southwest has occurred during the winter months when vegetation is typically dormant (which taps into the deeper soil moisture layers), the anomalously dry conditions are best captured by soil moisture percentiles in the near-surface layer of the SPoRT-LIS.  The total column SPoRT-LIS soil moisture percentiles does not depict an overly dramatic anomaly over the Desert Southwest (Fig. 3; unusual dryness is most prevalent in the deep layers from Oklahoma/Kansas up to Wisconsin/Illinois); however, the shallow soil moisture percentiles capture the anomalous drying over these regions near the surface, as seen in the animation of daily 0-10 cm percentiles for April  in Fig. 4, especially over West Texas, New Mexico and Arizona.  Medium-range forecasts suggest there could be precipitation over the Southern High Plains this weekend, but numerous wetting events will be needed to relieve the ongoing drought conditions.

Figure 1. NCEP Storm Prediction Center’s Day-1 fire weather outlook map for 17 April 2018.

Figure 2. Six-month change in SPoRT-LIS total column relative soil moisture for the period ending 16 April 2018.

Figure 3. SPoRT-LIS total column relative soil moisture percentiles, valid for 16 April 2018.

Figure 4. Daily animation of top-layer (0-10 cm) SPoRT-LIS soil moisture percentiles for the period 1 April to 16 April 2018.