June 23, 1998 Tornadoes near Rapid City, SD

Tornadoes

Tornado #1 - 15 mi North of Rapid City, SD Meade County Date June 23, 1998 Time (Local) 6:03 to 6:13 pm F Rating F0 Est. Peak Winds 85 mph Path Length Unknown Max Width Unknown Injuries/Deaths 0 Summary: A picturesque tornado developed in an open area north of Rapid City and remained nearly stationary. It was seen by many people in the Rapid City area. Photo of Tornado #1 by Molly Zeitler Photo of Tornado #1 by Tom Warner

Tornado #2 - 17 mi Northeast of Rapid City, SD Meade County Date June 23, 1998 Time (Local) 6:30 to 6:35 pm F Rating F0 Est. Peak Winds 85 mph Path Length Unknown Max Width Unknown Injuries/Deaths 0 Summary: About 17 minutes after the first tornado dissipated, a second, short-lived, thin tornado developed just to the east of the first. Photo of Tornado #2 Near Ellsworth AFB

Tornado #3 - 21 mi Northeast of Rapid City, SD Meade County Date June 23, 1998 Time (Local) 6:50 pm (end time unknown) F Rating F0 Est. Peak Winds 85 mph Path Length Unknown Max Width Unknown Injuries/Deaths 0 Summary: The third, and final, tornado developed due east and about 15 minutes after the second tornado dissipated. This was in open country. Based on radar data, this arguably was the "strongest" tornado. Photo of Tornado #3 by Ron Racicky Photo of Tornado #3 by Tom Warner

Tornado ratings are assigned based on the amount of damage they cause. The tornadoes in southern Meade County were rated using the original Fujita tornado damage scale (http://www.spc.noaa.gov/faq/tornado/f-scale.html). In 2007, the National Weather Service began using the Enhanced Fujita (EF) scale (http://www.spc.noaa.gov/faq/tornado/ef-scale.html), which is an updated F-scale developed by a team of meteorologists and wind engineers.

The Enhanced Fujita (EF) Scale classifies tornadoes into the following categories:

EF0 Weak 65-85 mph	EF1 Moderate 86-110 mph	EF2 Significant 111-135 mph	EF3 Severe 136-165 mph	EF4 Extreme 166-200 mph	EF5 Catastrophic 200+ mph

Radar

The tornado-producing storm was initiated downstream (downwind) of the Black Hills, about 20 miles northwest of Rapid City, at approximately 4:30 pm MDT. The storm quickly became severe, and soon developed a vivid hook echo (first image below, left), with strong convergent rotation (second image below, right) by 5:41 pm. The first tornado developed within this initial mesocyclone at 6:03 pm, about 15 miles to the north of downtown Rapid City. Note that the reflectivity features were not as striking at the time of the tornadic development as they were about 20 minutes earlier (see second row of images below). This initial tornado lasted approximately 10 minutes, becoming quite visually impressive, even from the Rapid City NWS office. At about this time, the radar showed a secondary appendage/hook echo quickly forming on the southwest flank of the initial storm.  By 6:30 pm, a thin, rope-like tornado formed east of this new mesocyclone/appendage, which lasted about 5 minutes. At this time, the storm exhibited two strong mesocyclones and appendages (hooks). As the storm slowly progressed to the east, the primary (eastern) mesocyclone strengthened considerably and produced the third tornado from this storm at 6:50 pm. This was the last confirmed tornado with this storm, though it continued to exhibit strong rotation for over another hour or two. This series of tornadoes was perhaps one of the best observed tornadic events from Rapid City, as all three were easily visible from many locations.

Radar Images for Tornado #1

Radar reflectivity at 5:41 pm, 22 min prior to tornado #1	Radar velocity at 5:41 pm, 22 min prior to tornado #1

Radar reflectivity at 6:02 pm, 1 min prior to tornado #1	Radar velocity at 6:02 pm, 1 min prior to tornado #1

Radar Images for Tornado #2

Radar reflectivity at 6:32 pm, 2 min after to tornado #2 developed	Radar velocity at 6:32 pm, 2 min after to tornado #2 developed

Radar Images for Tornado #3

Radar reflectivity at 6:52 pm, 2 min after to tornado #3 developed	Radar velocity at 6:52 pm, 2 min after to tornado #3 developed

Radar Algorithm Output for all Tornadoes

Here is a listing of the WSR-88D tornado detection algorithm (TDA) algorithm output for this event. TVS stands for tornadic vortex signature, which is a tight rotational couplet observed by the WSR-88D at the lowest elevation scan (0.5 degrees). ETVS is an elevated TVS that is not evident on the lowest elevation of the radar (i.e., it is above 0.5 degrees).

Environment

The atmosphere was very unstable throughout much of the early afternoon of June 23rd, with weak (20 kt or 23 mph) southwest flow aloft. Several strong, but transient storms formed in this unstable (CAPE ~ 2000 J/kg,  lifted index = –6) environment in a convergent area downstream (to the northeast) of the Black Hills (approximately 20 miles north-northwest of Rapid City). Some large hail (up to 1.75" diameter) was reported with these short-lived early afternoon storms. From 1:00 to 4:00 pm, the atmospheric wind shear increased significantly (as the surface winds strengthened out of the southeast), and the atmosphere further destabilized (CAPE ~ 4000 J/kg, lifted index = –13), allowing for the explosive formation of more organized (supercellular) tornadic storms. The atmospheric conditions within which the storms developed are well represented by the skewT/logP and hodograph displays from the June 24th, 00Z (6:00 pm MDT, June 23rd) Rapid City sounding (seen below). More information about the displays below can be found here.

SkewT/lopP display from the weather balloon released at NWS Rapid City (valid 6 pm MDT)	Hodograph display from the weather balloon released at NWS Rapid City (valid 6 pm MDT)

The surface maps showed a southeast surface wind that was bringing moist and unstable air into the Black Hills area. Temperatures at the Rapid City Airport from 3:00 to 5:00 pm where around 77°F and dewpoints were 65-66°F. This air was feeding into the tornadic thunderstorm to the north of Rapid City.

Surface weather map centered on the Black Hills (valid 3 pm MDT)	Surface weather map centered on the Black Hills (valid 5 pm MDT)