Motorcyclist fatally wounded by lightning while riding on the Boulder Turnpike during rush hour
"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.
On 21 June 2006, a 46 year old male motorcyclist was traveling westbound on Highway 36 (Boulder Turnpike) in
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.
Figure 1 Map of location where motocyclist was struck. Click on image for larger view. Map imagery from Google.com
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 “
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.
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.
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.