Jefferson County, Colorado lightning fatality of 21 June 2006:
Motorcyclist fatally wounded by lightning while riding on the Boulder Turnpike during rush hour

Stephen Hodanish
National Weather Service
Pueblo, Colorado

Gregory Stewart
Lightning Reference Center
Boulder, Colorado

This research is part of the Lightning Casualty Case Study section of the Colorado Lightning Resource Page, NWS Pueblo, Colorado. 

"The primary reason for these lightning casualty case studies is to observe where victims were located relative to thunderstorm activity when they were struck".

NOTE: on 15 September 2006, a few amendments and corrections were made to this document.

      Introduction

On 21 June 2006, a 46 year old male motorcyclist was traveling westbound on Highway 36 (Boulder Turnpike) in Westminster, CO. At approximately 511 pm MDT (2311 UTC), he was struck and killed by a lightning flash 4,277 feet east of the Church Ranch Boulevard overpass. After being struck, the motorcycle and rider veered to the left and made initial contact with a raised cement median barrier 4129 feet from the overpass. The rider flipped over the barrier and landed in the westbound lanes 4053 feet from the overpass, while the motorcycle continued to careen off the barrier and eventually came to rest in the westbound lanes 3839 feet  of the overpass. Both the rider and motorcycle were not hit by any other vehicle(s) during the accident.

Information acquired from the Colorado Traffic Accident Report indicated a small crater was found in the left hand lane of westbound Boulder Turnpike 4,277 feet east of the Church Ranch Boulevard overpass (geographically, this location was south-southeast of the overpass; see figure. 1). This crater was believed to be the location where the lightning flash made contact with the ground. This crater was measured to be 18” long, 8” wide and 4 inches deep. This crater location matches the location of where motorists observed the motorcycle and rider being struck by the flash. The motorists also reported “debris” hitting their vehicles immediately after the flash. This debris was believed to be asphalt from the crater location.

An autopsy report indicated the cyclist died from injuries from the lightning flash, and not the ensuing crash into the median.


map showing location of fatal lightning strike to motorcyclist on the Boulder Turnpike on 21 June 2006

Figure 1 Map of location where motocyclist was struck. Click on image for larger view. Map imagery from Google.com

            Data Analysis

In order to observe which lightning flash caused the fatality, two pieces of information need to be known. The first piece of information is knowing the exact time when the lightning flash hit the victim, and the second is the location of where the victim was struck. Typically, the victims' location is well documented. In this case study, the victim was not moved after the crash, and the crash site was well documented by media and emergency authorities.

The time of when the flash occurred is also believed to be highly accurate. The time of this incident was best estimated from the Westminster County, Colorado 911 dispatch records.  According to Westminster county Sheriff authorities, the first call came into the dispatch center at 5:12 MDT (2312 UTC). Audio files of the incident indicated the witnesses called the dispatch center immediately after the flash occurred.

Once the temporal and spatial information is known, then it is a matter of reviewing the National Lightning Detection Network (NLDN) data set and observe which flash caused the casualty at the location and time found above. The NLDN data set revealed 2 flashes occurred in the immediate vicinity of where the cyclist was struck. The first flash (-19 kA), occurred at 2311:20 UTC (5:11:20 pm MDT), while the second flash (-13 kA) occurred one second later, at 2311:21 UTC (5:11:21 pm MDT). It is likely that these two flashes were actually 1 flash which made contact with the ground in 2 separate locations (Fig 2). The first contact point was located at 39.876705 north latitude, 105.058441 west longitude.This was 1,281 feet east of where the crater was found in the road. The second flash was located at 39.862606 north latitude, 105.036011 west longitude. This second flash was located 7316 feet to the southeast of the first flash. Figure 3 shows a plot of the 2 flashes along with radar data as seen on the National Weather Service Warning Environment Simulator display system.


Figure 2. An example of a single lightning flash making contact with the ground in 2 different places. Photo: Copyright Steve Hodanish.





Figure 3. Radar and lightning data in the Westminster CO area (click on image for larger view). Lightning data shows the cloud to ground lightning activity which occurred between 23:11:00 and 23:11:59 UTC. The lightning data is marked with a white "-". The flash just to the left of the word “Westminster” in the center of the image above is the flash which caused the fatality. Radar data was from the National Weather Service Doppler radar site KFTG. KFTG is  located just southeast of the Denver International Airport, or 28 miles to the east-southeast of where the lightning fatality occurred.


In order to observe the trends in lightning activity prior to the cyclist being struck, lightning and radar data was analyzed over a 400 square mile (20 x 20 ) area, centered at the location of where the fatality occurred. The time of this analysis was from the time the cyclist was struck (2312 UTC) to 30 minutes prior (2241 UTC).

Analysis of this data indicated convective showers producing light to occasionally moderate rain were moving east at 15 mph across the region. The overall lightning activity with these showers was quite infrequent, as only 18 cloud to ground flashes were detected during this 30 minute time period. A majority of these flashes (13) occurred prior to 2252 UTC. The remainder of the flashes (5) occurred between 2256 and 2303 UTC. No flashes were detected between 2303 UTC and the time of the fatal flash (2311:20 UTC). Figure 4 shows a loop of the composite radar and 1 minute cloud to ground lightning data during this 30 minute time period.

At the time of the fatal flash, KFTG Doppler weather radar was indicating reflectivity echoes of 40-45 dBz were located to the immediate west and southwest of where the flash occurred. Radar echoes of 40-45 dBz  typically indicate moderate rain.

Loop of radar and 1 minute lightning data for 21 June 2006 in the Westminster CO area

Figure 4. Loop of Radar and Lightning data (Click on image for larger view). Loop of "1 minute" lightning data runs from 2241 to 2321 UTC (40 minutes). Radar data is composite reflectivity data from National Weather Service Doppler weather radar KFTG. Note that in the above loop, the "1 minute" lightning data shows all of the cloud to ground lightning that occurred during that one minute time period; i.e., "1 minute lightning plot Wed 22:42" indicates all of the lighting which occurred between 22:41:00 and 22:41:59). In the above loop, The 1 minute lighting plots change every minute while the radar data changes every 5-6 minutes. The reason for this is It takes 5-6 minutes to generate one composite radar reflectivity image. The "time date stamp" of the radar data denotes the time the radar image began.

        Discussion

It is unknown if the cyclist knew of the lightning threat in this case. The author is unaware of the time and location of when and where the cyclist began his commute. Assuming the cyclist had been commuting 20 minutes prior the the the lightning strike, it is possible that he may have seen some or all of the 5 flashes during the time period between 2256 and 2303 UTC as he traveled westbound on the Boulder Turnpike. Even if he did see the flashes, he may not have thought the threat was significant as the flashes were occurring a few miles away from the turnpike. Additionally, no cloud to ground lightning occurred in the 400 square mile region 8 minutes up to the time of the fatal flash. 

A witness who observed the cyclist being struck (this witness was immediately behind the cyclist in an automobile) reported that rain had just begun to occur prior the the fatal flash. This witness did not remember seeing any lightning occurring prior to the cyclist being struck.

Assuming the cyclist did not see any lightning, his only indication of the threat would have been the dark cloud bases over the region and the rain beginning to occur.

        Conclusion

This case is very similar to other lightning casualty case studies examined in the past. That is, a large majority of people who are being struck by lightning are being struck by storms which produce only an occasional cloud to ground lightning flash. For more information about these cases, please click here.

It is very important that if you see lightning (even if it is "in the distance"), or hear thunder, you should seek safe shelter. Safe shelter is a large enclosed substantial building, or a hard topped vehicle.

This is not the first time a cyclist has been struck and killed by lightning in Colorado. Another case study of a cyclist being struck and killed by lightning can be read by clicking here.

 



 



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