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.

GLM-HSVAWW-20180530_232040

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.)

GLM-HSVAWW-20180531_005836

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.

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.

GOES-16 ABI and GOES-R CI aid IDSS over the weekend

Once again, NWS Huntsville provided impact-based decision support services (IDSS) for the Panoply Arts Festival in downtown Huntsville.  Since it occurs in late April every year, Panoply has a long history of coping with challenging weather conditions, and NWS Huntsville has staffed the event every year to help with those challenges.  This year was no exception.

 

Saturday was a summer-like day, with the main forecast challenge being convective initiation from a field of cumulus clouds.  The UAH-developed GOES-R Convective Initiation algorithm output was helpful with this process as it correctly forecast low probabilities for much of the day.

 

We also decided to look at GOES-16 ABI data to see if it added any value.  In addition to monitoring the low (7.3um) and mid-level (6.9um) water vapor channels on a larger scale, the Red Visible (0.64 micron) was most beneficial.  A mesoscale domain sector was in place over the region at the time, enabling forecasters to easily look for growing cumulus clouds (though there were not many of these).  (Apologies for the quick and small screen captures!)

GOES-16 ABI 0.64um imagery – valid 29 April 2017 1950 UTC

During the mid-afternoon, forecasters staffing the emergency operations center noticed an interesting trend in the visible imagery: areas to the south that were shrouded by thicker cirrus were seeing clearly-suppressed cumulus development, and the cumulus clouds were developing again once the cirrus had passed by. This almost created a “moving shadow” effect.

GOES-16 ABI 0.64um imagery – valid 29 April 2017 2013 UTC

GOES-16 ABI 0.64um imagery – valid 29 April 2017 2029 UTC

The forecasters were able to use this to determine that convective initiation–and thus impacts to Panoply and downtown Huntsville–were very unlikely, since the cirrus clouds were moving into the area.
There is a great deal of promise for IDSS using the new GOES-16 data, particularly once the Geostationary Lightning Mapper begins flowing on a preliminary basis.
Note The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

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.

Total Lightning Highlights Trailing Stratiform Threat for IDSS

NWS Huntsville is providing Impact-Based Decision Support Services (IDSS) to protect life and property at an outdoor sporting competition in the Decatur, Alabama area this week.  A decaying Mesoscale Convective System (MCS) moved across north Alabama this afternoon, forcing a delay in the competition for several hours.  While the North Alabama Lightning Mapping Array (NALMA) helped determine what to tell local emergency managers about the start of the lightning threat, the NALMA really shined in trying to figure out when the lightning threat would end.

KGWX Radar Reflectivity and North Alabama Lightning Mapping Array, valid 1949 UTC 14 July 2016

KGWX Radar Reflectivity and North Alabama Lightning Mapping Array, valid 1949 UTC 14 July 2016

The example images include NALMA Flash Extent Density data, which are represented by irregular pink and purple shapes displayed over the KGWX radar reflectivity.  Both the 1949 and 2007 UTC indicate scattered very low flash rates extending over a broad area–including the Decatur area–suggesting occasional in-cloud flashes within the trailing stratiform region of the MCS.  This is a known threat with MCSs, but it was not clear at the time how long the lightning threat would persist.  Use of total lightning information from NALMA enabled NWS Huntsville staff to determine that the lightning threat would not subside until rain subsided.

KGWX Radar Reflectivity and North Alabama Lightning Mapping Array, valid 2007 UTC 14 July 2016

KGWX Radar Reflectivity and North Alabama Lightning Mapping Array, valid 2007 UTC 14 July 2016

With the launch of GOES-R and the Geostationary Lightning Mapper, these kinds of data will improve lightning-based IDSS across a much wider cross section of the CONUS.

LEO Perspective of River-Effect Snow in North Alabama

The cold air outbreak over the eastern United States had impacts far and wide, including the development of snow showers all the way into northern Alabama.  However, between unseasonably low 850 mb temperatures and northwesterly flow, the outbreak also caused a semi-persistent band of snow to develop along the Tennessee River (downwind of a reservoir known as “Lake Wheeler”).

While most of the river-effect monitoring occurred with radar, the late-morning MODIS overpass captured one of the narrow river-effect bands (and did so more effectively than the lower-resolution GOES-East Imagery).

2016-02-09-1644_LESBand-LEO-wLakes-Aug

Figure 1. MODIS visible image, valid 1644 UTC 9 February 2016.  Larger lakes are outlined in blue, and the river-effect band is circled in yellow.

Snowfall reports from underneath the band have indicated 2 to 3 inches of snow, compared to the 1-2 inches reported with heavy or persistent snow showers elsewhere.  Unfortunately, orbit timing and cloud cover have not allowed us to view the snow swath using the Snow-Cloud RGB.  However, the Snow-Cloud RGB from the edge of this morning’s MODIS pass still illustrated the river-effect band persistence.

SnowCloud_10Feb2016_Aug

Figure 2. MODIS Snow-Cloud RGB image, valid 1549 UTC 10 February 2016.  The Tennessee River is the dark blue feature in the center of the image; the river effect band is circled in red.

LMA Flash Extent Density Data Used for Warning Decision

The Huntsville office has a long history of using total lightning information from the North Alabama Lightning Mapping Array (NALMA) for warning decision-making.  Since 2003, WFO Huntsville has been ingesting and receiving a source density product from NASA SPoRT.  However, recently, we decided to begin migrating to Flash Extent Density (FED) data; this is more consistent with the Geostationary Lightning Mapper, more consistent with recent operational research, and easier to convey and understand.  Typically we are trying to apply the “two-sigma” lightning jump algorithm suggested by Schultz et al. (2009, 2012).

On June 8, a weak front moved across the Huntsville forecast area, initiating development of strong to severe thunderstorms.  An 1800 UTC sounding from Redstone Arsenal indicated a relatively high threat for wet microbursts.

One of the storms moved across extreme southern Jackson and northern DeKalb Counties in northeast Alabama.  I was viewing the NALMA FED data and watched as the storm went from less than 10 flashes, to 40 flashes, in three “scans” (from 2214 to 2218 UTC).  (Interestingly, despite using SAILS with the KHTX radar, AWIPS-2 matched all three lightning images to a single 0.5-degree radar scan.)

2015-06-08-2214

Fig. 1: KHTX Reflectivity valid 2215 UTC and NALMA FED valid 2214 UTC 8 June 2015

Fig. 2: KHTX Reflectivity valid 2215 UTC and NALMA FED valid 2216 UTC 8 June 2015

Fig. 2: KHTX Reflectivity valid 2215 UTC and NALMA FED valid 2216 UTC 8 June 2015

Fig. 3: KHTX Reflectivity valid 2215 UTC and NALMA FED valid 2218 UTC 8 June 2015

Fig. 3: KHTX Reflectivity valid 2215 UTC and NALMA FED valid 2218 UTC 8 June 2015

Since we cannot get the formal lightning jump algorithm into AWIPS-2 at this time, forecasters need to do some quick mental math to decide if jumps such as these constitute a real jump.  I was certain this did (and later Excel work verified this) so I issued a severe thunderstorm warning, despite the storm being very close to the Georgia state border.

This storm produced structural damage in the Cartersville community near the state line shortly after the warning was issued, tearing the roof off of an apartment complex and downing trees and powerlines.  There was not much lead time (there rarely is with these kinds of storms) but this reinforces our past experience with total lightning–and reinforces that lightning may be especially useful during a challenging warm season warning environment.