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Archive for the ‘Lightning Mapping Array’ Category

Here at the Huntsville, AL Weather Forecast Office (WFO) we’ve pointed out total lightning data’s operational utility a number of times in this blog.  After all, the data have been a rather integral part of our severe weather operations for at least 13 years.  Anyway…I’m going to do it again.  I think it can be beneficial to reiterate the value of certain data sets from time to time, especially to reemphasize their operational utility to new members of the forecasting and research community and perhaps newcomers to the SPoRT blog.

This afternoon and evening was a somewhat typical summertime convective event for the Tennessee Valley.  Showers and thunderstorms developed in the early afternoon and gradually increased in coverage and intensity during the mid to late afternoon hours.  By the time I arrived on shift at about 3 pm CDT, a few thunderstorms were showing signs of intense updrafts (~50 dBZ at the -10C isotherm level), but were still not to the level of producing severe weather.  Nevertheless, multiple outflow boundaries interacting with the hot, humid and unstable airmass caused decent coverage of shower and thunderstorm activity, especially in northeastern portions of Alabama during the mid afternoon into the early evening.  A few thunderstorms contained strong updrafts, heavy rainfall, frequent lightning and wind gusts up to about 40 mph.  The first of these started showing signs of strengthening in eastern portions of DeKalb County, AL shortly after 3 pm CDT.  The first image below (image 1) shows a snapshot of total lightning data (flash extent density) from the North Alabama Lightning Mapping Array (NALMA) at 2014 UTC.  Values at this time in the developing storm were just around 10 flashes per 2-minutes.  By 2022 UTC however, flashes had increased to nearly 50 flashes per 2-minutes (Image 2).

Total Lightning (per North Alabama Lightning Mapping Array), 23 July 2016 2014 UTC

Image 1. Total Lightning (per North Alabama Lightning Mapping Array), 23 July 2016 2014 UTC

Image 2.

Image 2.  Total lightning (per NALMA), 23 July 2016 2022 UTC

Importantly, increases in total lightning activity are directly related to updraft strength within storm cells so it was no surprise that reflectivity values increased correspondingly.  The next two images show the increases in Multi-radar Multi-sensor (MRMS) isothermal reflectivity (dBZ) at the -20 C level during the same period (Images 3 and 4).

Image 3. Multi-radar Multi-sensor isothermal reflectivity (dBZ) 23 July 2016 2014 UTC

Image 3. Multi-radar Multi-sensor isothermal reflectivity (dBZ) at -20 C over portions of NW Alabama and NW Georgia, 23 July 2016 2014 UTC

 

Image 4.

Image 4.  Multi-radar Multi-sensor isothermal reflectivity (dBZ) at -20 C over portions of NE Alabama and NW Georgia, 23 July 2016 2022 UTC

Data such as the MRMS isothermal reflectivity when used in conjunction with other data such as total lightning (or flash extent density) allow for a good evaluation of updraft development within thunderstorms and their evolution through time.  Environmental parameters on this day suggested that severe weather was not likely.  Nevertheless, the strengthening updrafts were followed by wind gusts around 30 to 40 mph, which were recorded at a few of our surface observation sites.  Special Weather Statements were used to address this marginal thunderstorm threat during the afternoon and evening.  Interestingly, notice that the total lightning data at 2022 UTC (Image 2) indicated that the updraft in the northern cell in DeKalb County was perhaps the strongest at the time (due to higher values on flash extent density), while MRMS reflectivity values were higher at the same time in the southern cell (image 4).  Subsequently, the northern cell strengthened and became the dominant cell over the next 30 minutes.  On days such as this when there are often multiple thunderstorms ongoing at any one time, and this happens often here in the TN Valley in the summertime, total lightning data can be an effective situational awareness tool for evaluating storms that are undergoing strengthening and helping to provide proper focus for operational meteorologists.

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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.

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The SPoRT Center regularly works to display unique data in products, such as total lightning from ground-based lightning mapping arrays (LMAs), in the Weather Service’s display system; AWIPS II.  However, there is occasionally an opportunity to try a different method for specific operational applications.  One of those opportunities came with the Morristown, Tennessee forecast office.  Here, the collaboration was looking for a web-based visualization in order to better collaborate with emergency managers.  Feedback to SPoRT requested the need for a real-time display that could animate the data, auto-update, and allow zooming to a feature that would not reset with an update.  Additionally, there was a need to make this functional on mobile devices.

This has resulted in the test display shown here of the North Alabama Lightning Mapping Array flash extent density from July 1, 2015 from 1:30-4:00 PM (Central).  Like the more traditional display in AWIPS II, this flash extent density highlights the main storm cores where the updraft is intensifying, shows the spatial extent of total lightning, and even highlights several long flashes into the stratiform region behind the main convection, as shown in the still images below.  While the display is just in a development state now, it is demonstrating the potential for how to bring these data to emergency managers and Weather Service forecasters who may be in the field and not in the office, such as for special outdoor events.

Demonstration total lightning web display

The North Alabama Lightning Mapping Array flash extent density animation from 1:30-4:00 PM (Central) on July 1, 2015 in a new demonstration web display.  State and county boundaries are in black, while interstates are blue and major U.S. highways are in red.  (Click for the full resolution image.)

The two images below show a still image from 2:14 PM (Central) of the total lightning flash extent density and the corresponding radar reflectivity.

A still taken from the animation above at 2:14 PM (Central).  The main storm core and stratiform region lightning are highlighted.

A still taken from the animation above at 2:14 PM (Central). The main storm core and stratiform region lightning are highlighted. (Click for the full resolution image.)

 

The corresponding radar reflectivity at 2:14 PM (Central) for the still image above highlighting the locations of the total lightning features.

The corresponding radar reflectivity at 2:14 PM (Central) for the still image above highlighting the locations of the total lightning features. (Click for the full resolution image.)

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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.

 

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On the evening of Monday, October 6th, several severe thunderstorms producing large hail moved across the Tennessee Valley region.  I, along with another colleague, was on the radar desk for severe weather operations at the Huntsville, AL Weather Forecast Office.  Some thunderstorms in the region had already produced large hail up to the size of golf balls to our north.  As a vigorous short wave moved through the region, leading to increased lapse rates and deep layer shear, the threat for large hail was expected to continue into the early evening hours.  As usual here at the Huntsville WFO, total lightning data from the North Alabama Lightning Mapping Array (NALMA) were incorporated into our warning decision process.

At 548 pm CDT, my colleague  issued an initial severe thunderstorm warning for a storm cell located over northwestern portions of Jackson County, AL, primarily for the expectations of large hail.  Reflectivity from the KHTX radar and the initial polygon can be seen below in image 1.

Reflectivity0.5_JacksonCounty_Oct62014-7

Image 1.  KHTX 0.5 degree reflectivity (dBZ) with warning polygon issued at 2248 UTC (548 pm CDT) 6 Oct 2014. The black circle near the top center of the image is the KHTX “cone of silence”.

I had taken over warning responsibility for this severe thunderstorm by 6 pm and was having to decide whether or not to continue the warning when it expired at 615 pm CDT.  This storm was tracking very close to the KHTX radar (noted by the black circle) and it was difficult to make out some of its higher level features and characteristics (although the Advanced Radar for Meteorological and Operational Research (ARMOR) was also being utilized at this point).   The storm had wavered in intensity since the warning issuance and was only expected to be at the low-end of severe criteria.  Another factor complicating the warning decision was that this storm was tracking over an area with very low population density.  So, severe weather reports providing ground-truth were difficult to come by, and in fact, we had not received any yet allowing for verification of the warning.

Nevertheless, this is where the NALMA data came into play.  Just shortly after the severe thunderstorm issuance, source densities within the storm surged, with values reaching well over 400 sources (image 2) between 550 and 552 pm CDT.

Source density values from the North Alabama Lightning Mapping Array, 2-min period ending 552 pm CDT (2252 UTC) 6 October 2014.

Image 2. Source density values from the North Alabama Lightning Mapping Array, 2-min period ending 552 pm CDT (2252 UTC) 6 October 2014.

 

Over the next series of updates from the NALMA, source densities maintained relatively high values.  As late as 2302 UTC, when I was beginning to consider the continuance of the warning, source values were still around 400 or higher.  Afterward, values did gradually decrease.  However, with the understanding that hail production will take some time following the strengthening updraft and that severe weather may not manifest up to about 30 minutes (or longer in some cases) after sustained surges in total lightning, I decided to continue the warning (Image 3).  As the storm continued eastward, we finally received our first reports of one inch diameter hail in the town of Stevenson.  Interestingly, the hail accumulated to the depth of a few inches according to one report.

So, yet again, this was another case in which total lightning provided value-added data and significant help for an operational warning decision.

Stevenson

Image 3. KHTX 0.5 degree reflectivity with warning polygon (yellow), valid 617 pm CDT 6 October 2014. The town of Stevenson, AL is highlighted where one inch diameter hail was reported covering portions of Hwy 72.

 

 

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We have a long history of usage of total lightning data via the North Alabama Lightning Mapping Array (LMA) data here at the National Weather Service office in Huntsville, AL. LMA data began flowing here way back in the spring of 2003.  There have been minor interruptions of data at times, mainly during and shortly after the implementation of AWIPS II, but total lightning data have been an integral, consistent part of operations here for over 10 years.  These data have been used most often for detecting the initiation of electrical activity in developing convection.  This is important because studies show that intra-cloud lightning often precedes cloud-to-ground lightning by about 5 to 10 minutes.  Thus, total lightning data can serve as an early warning signal of the more dangerous cloud-to-ground component.  We’ve also used the data to help identify thunderstorms that may experience rapid intensification, since total lightning activity is directly related to strengthening updrafts.  I’ve even posted about an event in March 2012 where I used the LMA data as supplemental evidence that helped prompt a severe thunderstorm warning.  This past Sunday evening (August 10th) I had the opportunity to use the data in a unique way (at least for me)…to help with a flash flood warning decision.

The first image below is a loop of KHTX WSR-88D 0.5 Reflectivity from this afternoon.  Notice the cell that developed and persisted over northwestern portions of Morgan County.  This cell developed directly along the Tennessee River and over the city of Decatur, AL.

Image 1.  KHTX 0.5 deg reflectivity 1920-2112 UTC 10 August 2014

Image 1. KHTX 0.5 deg reflectivity 1920-2112 UTC 10 August 2014

The cell was producing heavy rainfall, and the other operational forecaster and I were watching it closely.  One-hour rainfall amounts shortly after 2100 UTC were approaching 2 inches according to KHTX and nearby ground stations, which was near flash flood guidance for basins in this area.  Of course, we were also dealing with data latency from these various sources, which is generally anywhere from about 5 to 20 minutes or more depending on the source. In a flash flooding situation, just as any other warning situation, things can evolve quickly and data updates as fast as possible are desired.

Perhaps most concerning however, was the fact that this cell was back-building and showing signs of little movement during the period, while some of this rain was falling over the city of Decatur. True, Decatur is a relatively small city, but still has sufficient urban land cover, and is bordered to the north and east by terrain that slopes gently toward the Tennessee River. So, drainage of water can be slow in the city, especially once adjacent backwaters and wetlands associated with the Tennessee River fill with water. While considering a flash flood warning, I still wanted some idea of the potential longevity of the cell over the Decatur area.  The area could have handled this much rainfall if the cell dissipated and/or moved off as most others were prone to do in the low shear environment that day. However, looking at the LMA data really helped with my decision.  Beginning at approximately 2104 UTC, source (image 2) and flash data (not shown) from the LMA showed the beginning of an enormous increase in total lightning activity with this cell.  Also, the increase was taking place directly over the city of Decatur.

Image 2.  KHTX 0.5 degree reflectivity overlaid with North Alabama LMA source density 2104-2134 UTC 11 August 2014

Image 2. KHTX 0.5 degree reflectivity overlaid with North Alabama LMA source density 2104-2134 UTC 10 August 2014

This trend in total lightning continued over the next several minutes.  With the knowledge that this cell was likely undergoing intensification and moisture-laden updrafts were strengthening directly over the city of Decatur, I decided to issue the flash flood warning, which was officially disseminated at 2115 UTC.  We received the first reports of flash flooding at 2145 UTC.  The next image below shows the location of the warning issuance.

KHTX 0.5 degree reflectivity with Flash Flood Warning polygon (green box) 2117 UTC 10 August 2014

KHTX 0.5 degree reflectivity with Flash Flood Warning polygon (green box) 2117 UTC 10 August 2014

The total lightning data in this case served as a very valuable severe weather application tool.  By providing the warning forecaster with knowledge of the location and likelihood of future deep convection, a flash flood warning was issued in a more timely and effective manner than would have been possible without these data.  When used in conjunction with other information and applied properly, these types of data can help to save lives and property.

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In late April,  NASA SPoRT and the Albuquerque NWS met with scientists at New Mexico Tech to coordinate the integration of the Langmuir Lab lightning mapping array data into our operations.  According to Bill Rison, Paul Krehbiel, and Ron Thomas, New Mexico Tech’s Lightning Mapping Array (LMA) is a 3-dimensional total lightning location system. The system is patterned after the LDAR (Lightning Detection and Ranging) system developed at NASA’s Kennedy Space Center by Carl Lennon, Launa Maier and colleagues. The LMA measures the time of arrival of 60 MHz RF radiation from a lightning discharge at multiple stations, and locates the sources of the radiation to produce a three-dimensional map of total lightning activity.  The time-of-arrival technique for studying lightning was pioneered by Dave Proctor in South Africa.  The NASA SPoRT core project site details that operationally, total lightning data provide several advantages to forecasters.  First, total lightning data often give a 3-5 minute lead time ahead of the first cloud-to-ground lightning strike.  This improves lightning safety for the National Weather Service’s Terminal Aerodrome Forecasts (TAFs) and Airport Weather Warnings (AWWs).  This safety feature also can be used for incident support of special events. In addition, the total lightning data provides information about the spatial extent of lightning that is not available in the traditional cloud-to-ground data (http://weather.msfc.nasa.gov/sport/lma/).  This data may also be used to evaluate the degree of lightning activity within active wildfire smoke plumes.  The image below is an example of an LMA station at Briggsdale, Colorado taken by New Mexico Tech.  These stations are solar-powered and communications are operated via cell technology.

LMA stations at Briggsdale, Colorado.  Photo available from NM Tech.

Figure 1.  LMA station at Briggsdale, Colorado. Photo available from NM Tech.

After the first collaboration between NWS Albuquerque and NM Tech, forecaster Jennifer Palucki met with Harald Edens in June to install the xLMA and Live LMA software onto our office outreach laptop.  The LMA data that forecasters are evaluating at Albuquerque consists of source densities.  The imagery is available as a contour shaded product and describes the overall extent of sources from a particular thunderstorm or complex of thunderstorms.  The Live LMA software provides the actual point source information that make up the densities available in AWIPS.  The forecaster can actually see the structure of the point sources making up a flash on a 1-minute temporal resolution.  Figure 2 below shows the composite radar reflectivity valid at 0200 UTC July 23, 2014 for a complex of thunderstorms developing southward into the Albuquerque Metro Area.  The associated LMA source density product at 0202 UTC in Figure 3 illustrates the structure of the shaded point sources for the lightning flash.  The graphic shown in Figure 4 details the point sources available with the Live LMA software.  The source densities making up the flash during this 1-minute period stretched as far as 30-km from north to south and 20-km from east to west.  The altitude of the main source region was near 10-km.  The data available in AWIPS also allows the forecaster to slice and dice the data by elevation angle.  Forecasters at the Albuquerque NWS will continue evaluating the LMA products through summer 2014 to offer feedback to NASA SPoRT and NM Tech on its operational application.

 

Figure 2.  Mosaic Composite Reflectivity valid at 0200 UTC July 23, 2014.

Figure 2. Mosaic Composite Reflectivity valid at 0200 UTC July 23, 2014.

 

Figure 3.  Langmuir Lab LMA Source Density product valid at 0202 UTC July 23, 2014.

Figure 3. Langmuir Lab LMA Source Density product valid at 0202 UTC July 23, 2014.

Figure 4.  Live LMA 1-minute point sources valid at 0202 UTC July 23, 2014.

Figure 4. Live LMA 1-minute point sources valid at 0202 UTC July 23, 2014.

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