This paper was presented at the 17th International Lightning Detection
Conference held in Tuscon, AZ, October 2002.
Using sounding and radar data, this paper will examine a shallow convective updraft which produced a cloud to ground lightning flash which fatally wounded an 18 year old male on top of Pikes Peak, Colorado (elevation 4.3 km above MSL; Figure 1). The young male was standing in an exposed boulder field approximately 33 meters from the top. Two other companions were nearby, but not injured. Each were spaced approximately 10 meters apart. The first companion closest to the teen who was fatally struck was knocked to the ground. The other was still standing after the flash. According to eyewitnesses, no thunder was heard prior to the fatal flash. The fatal flash occurred just prior to 1900 UTC on 25 July, 2000.
2. DATA ANALYSIS
NLDN data collected on the National Weather Services Advanced Weather Interactive Processing System (AWIPS) indicated only 1 flash occurred in the Pikes Peak region between1800 UTC and 1900 UTC (Figure 2). A review of lightning data during this hour indicated no other flashes occurred within 90 kilometers of the Pikes Peak massif. This single flash occurred at exactly 18:56:50 UTC (11:56 Central Standard Time), and was located at latitude 38.841N, longitude 105.040W, or the top of Pikes Peak. Seven other cloud to ground flashes were noted between 1900 UTC and 2000 UTC in the greater vicinity of Pikes Peak, but occurred over 10 kilometers to the south of where the fatal flash occurred.
2.2 Radar Analysis
The electrification process within a cumulonimbus cloud requires small
hail pellets, called graupel. Radar studies have shown that high concentrations
of graupel are
Figures 4 through 8 shows radar reflectivity data of the cell which
produced the lightning flash over Pikes Peak. Both composite reflectivity
(defined as the maximum
The first discernible precipitation echo (>= 18 dBZ) associated with the cell which would produce the fatal flash was identified at 1841 UTC (Figure 4a). The accompanying cross section for this cell (Figure 4b) showed this small 22-27 dBZ echo just west of Pikes Peak massif extending to 6.1 km above MSL. The following volume scan (1846 UTC, Figure 5a-b) indicated the cell had grown both in height and in width. The cell now extended to an elevation of to 7.9 km above MSL, with a smaller core of 22-27 dBZ extending up to 5.8 km. By 1851 UTC (Figure 6a-b), the cell had continued to grow in width; extending horizontally 5 km just to the west of the Pikes Peak, but had decreased in height to 6.7 km. Reflectivity values had increased, and now ranged between 27-32 dBZ, and were in a layer between 5.2 and 5.4 km.
Examination of the Denver sounding indicated this layer was at the level
of the 0o C isotherm, and this layer of higher dBZ was likely
a mixture of graupel and
The 1856 UTC volume scan (Figure 7a-b) indicated the cell had increased in height once again, reaching up to 8 km. It was during this volume scan when the fatal cloud to ground lightning flash occurred. The most significant change between this image and the volume scan 5 minutes prior showed the maximum dBZ values (27-32 dBZ) now extended towards the ground, indicating the likelihood of frozen precipitation particles descending towards the ground. No reflectivity values of 35 dBZ or higher were noted in this volume scan, nor were they noted in the 1901 UTC radar volume scan (Figure 8a-b).
Prior research has shown cloud to ground lightning typically occurs when a radar echo of 35 dBZ or higher occurs at or above the height of the -10 oC level. The -10 oC level in this case was located at 6.1 km MSL. Radar analysis of this cell did indicate hydrometeors reaching above the height of the -10 oC level, but it did not show radar echoes greater than or equal to 35 dBZ reaching this level. This cell was also unique as it was quite shallow. Typical mid latitude convective updrafts reach up to 12 km (Weismann and Klemp, 1986), this cell reached a maximum height of 7.9 km.
The reason why this flash occurred may be explained by the isolated nature and height of the Pikes Peak massif. A cloud to ground lightning flash striking the top of Pikes Peak would have to travel a considerably shorter distance than if the same flash were to strike in nearby valleys or adjacent plains. Sounding data indicated the distance between the -10 oC level and the top of Pikes Peak was a mere 1.8 km. It is likely this reason why this storm with marginal radar characteristics was able to produce a cloud to ground flash.
This paper documents a shallow convective updraft which produced a cloud to ground lightning flash which fatally wounded a young male on top of Pikes Peak, Colorado. Radar data and lightning maps indicate this was the “first flash of the day” associated with this cell. Electrical characteristics of this storm did not follow known radar characteristics as the flash developed with lower radar thresholds than what is discussed in the literature. It is likely the relative isolation and height of Pikes Peak played a role in the development of this flash.
This case shows why people should be extremely cautious while hiking in the mountains during the thunderstorm season. Weak updrafts developing over high peaks can produce cloud to ground lightning flashes.
The authors would like to thank
(El Paso county search and rescue) for information regarding
the timing and specific location of the fatality,
Steve Goodman (NASA) for supplying information of the lightning flash,
and the staff of NWS Pubelo for their assistance with this document.
Figure 1. Topographical map (kft) withcounties labeled showing the Pikes Peak region. Pikes Peak is located in extreme west central El Paso county. KPUX (lower right) is the location of the radar used in this study.
Figure 2. One hour lightning plot map between
1800 and 1900 UTC 25 July 200. Three flashes (dashes) occurred during this
one hour time period. The flash in extreme west central El Paso county
is the top of Pikes Peak.
Figure 4a-b. KPUX Composite reflectivity data at 1841 UTC (a). The “X” in the center of the composite reflectivity plot marks the location of the top of Pikes Peak. Narrow line running southwest-northeast in (a) denotes the reflectivity cross section shown in (b). Height in (b) is measured with respect to mean sea level. Reflectivity bin values are as follows: light green (“18 dBZ”) range from 16-22 dBZ; mid green (“24 dBZ”) ranges from 22-27 dBZ; dark green (“29 dBZ”) range from 27-32 dBZ; and yellow (“34 dBZ”) ranges from 32-38 dBZ. See CD rom for colored images. The maximum reflectivity range at the 6.1 km level (20 kft) in (b) is 22-27 dBZ. Reflectivity scale in (a) and (b) are identical. Time stamp denotes when the volume scan began.