June 4, 1999 Oglala, SD, Tornado

Tornadoes:

Tornadoes - Kyle, Martin, Oglala, Pine Ridge, and Slim Buttes Oglala Lakota, Jackson, and Bennett Counties Date June 4, 1999 Time (Local) 6:30, 6:40, 7:10, 7:30, and 7:45 pm (end times unknown) F Rating F0 to F2 Est. Peak Winds 135 mph Path Length Estimated 15 mi (max) Max Width 400 yards Injuries/Deaths 1 fatality; 54 injuries Summary: A powerful tornado ripped through Oglala, with a total of five confirmed tornadoes on this day. Track Map

Tornado ratings are assigned based on the amount of damage they cause. The tornadoes in Oglala Lakota, Jackson, and Bennett Counties 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

Additional Facts

1. The Red Cross estimated that 123 homes sustained major damage, and an additional 139 sustained minimal damage. FEMA deemed 49 homes beyond repair, and were demolished.
2. One person was killed during this event, over 40 injured, and 22 had to be sent to area hospitals.
3. The one recorded death from this event was the first fatality from a tornado in western South Dakota since 1939, and only the third ever recorded in western South Dakota.
4. Very large hail also was reported in the area. Grapefruit-sized hail (4" in diameter, see the "Photos" section) was observed 2 miles west of Oglala, with golf ball and baseball-sized stones reported in Oglala.
5. At the time of this writing, it appeared that the storm complex responsible for the Oglala damage was intermittently producing tornadoes from 5:30 pm to almost 8 pm—for 2 1/2 hours.

Photos

NWS Storm Survey Photos

Drs. Brian Klimowski and Matthew Bunkers from the NWS office in Rapid City, SD, went to the Oglala area early on June 5 to conduct a damage survey and assess the severity of this event. The damage that was observed generally was in the F1-F2 range, with the most severe damage just to the east of the main intersection in Oglala. One, or perhaps two, tornadoes were responsible for the most severe damage.

With the lack of trees and structures in the area, it was difficult to identify any "path" of the tornado(es). If the tornado was retrograding at the time it struck Oglala (moving westward as it was rotating around the mesocyclone), the damage could have been caused by one tornado. However, if the tornado(es) were moving with the storm and low-level circulation, there likely would have been two tornadoes to explain the damage that was observed over the Oglala area.

The area in and around Oglala also experienced very strong straight-line winds from the north to northwest, which accounted for F1-type damage on the western and northern parts of Oglala. The images below are typical of what was observed north and south of the main intersection in Oglala, where F1-type damage was noted.

Large hail observed the day after the Oglala tornado

Further to the east, several locations experienced F2-type damage. The spread of the debris indicated that there was one, and perhaps two F2 tornadoes that affected the area. One such area was near the primary church in town. Below, you can see a mix of F1 and F2 damage---from the movement of framed structures off their foundations (below left), to the destruction of an unsecured framed structure that was tossed 80 feet (below middle), and the destruction of a mobile home that was sheltered within trees (below right).

One-half to three-quarters of a mile further to the east there was a more continuous region of severe (F2) damage. In this area, all of the telephone and utility poles were snapped and tossed, mobile homes were thrown over 100 yards (below left and middle) with debris strewn over a quarter of a mile, and a relatively "new" framed house was leveled (below right), with wood projectiles in the ground 100 yards downstream.

Radar

Radar images from the Oglala tornado event are below. The first image (below left) shows the storms as they appeared at 5:29 pm MDT, close to the time that the first tornadoes were reported in Nebraska. Though the storm was quite distant from the radar at this time, it exhibited may classic features of a severe supercell, including strong rotation, an appendage (possibly a "hook"), and a bounded weak echo region (BWER,  below right).

Radar reflectivity at 5:29 pm MDT on June 4, 1999	Radar reflectivity at 1.5 degree elevation at 5:19 pm MDT on June 4, 1999

An hour later, at 6:29 pm MDT (below) we received our first confirmation of a tornadoes in South Dakota. At this time, two tornadoes were reported west of Pine Ridge. The Doppler velocity image (below right) shows two areas of high gate-to-gate shear, indicating the possible position of these two tornadoes. The northernmost tornado was within the well-formed hook echo west-northwest of Pine Ridge. Note a second supercell to the southwest of the first storm, just entering South Dakota at this time (below left). This second storm also exhibited a hook echo, and eventually produced a tornado about 5 miles north of Pine Ridge.

Radar reflectivity at 6:29 pm MDT on June 4, 1999	Radar velocity at 6:29 pm MDT on June 4, 1999

At 6:40 pm, the tornadic storm moved into the Oglala area. The radar images below show that the extremely strong low-level circulation was just to the south of Oglala at this time. This coincides well with the damage which was observed in the area, with the most severe damage located just to the south and east of the main Oglala intersection.

Radar reflectivity at 6:40 pm MDT on June 4, 1999	Radar velocity at 6:40 pm MDT on June 4, 1999

The two storms that passed through the Oglala area slowly merged into one storm from 7 to 7:45 pm. At 7:50 pm, the storm assumed "high precipitation" supercell characteristics, with much precipitation wrapping around the mesocyclone. Several tornadoes also were sighted at this time near the town of Kyle. In summary, the loop of radar images (below right) demonstrates the evolution of the Oglala tornadic supercell.

Radar velocity at 7:50 pm MDT on June 4, 1999	Reflectivity loop from 4:54 to 8:10 pm MDT on June 4, 1999

Environment

The 4 June tornadic supercell developed within an environment which demonstrated the classic features for a tornadic event, including strong instability, high low-level moisture, strong vertical wind shear, and a midlevel short-wave trough moving through the area. This brief discussion discusses these features as they were exhibited during the 4 June Oglala tornado event. Data from 00Z on June 5th (6 pm MDT on June 4th) were used for most of the analyses.

Beginning with the higher levels of the atmosphere, the 500 mb height / vorticity at 00Z (below, from the 00Z analysis of the ETA model) exhibited an unseasonably strong and deep trough over the southwestern United States, with nearly meridional flow through the panhandle of Nebraska and western South Dakota. A relatively strong short-wave trough was evident in this flow moving to the north through the Panhandle of Nebraska and southwestern South Dakota. These features also are well-represented in the DIFAX charts at 300mb, 500mb, 700mb, and 850mb (see below).

Eta 500 mb heights/vorticity and vorticity advection at 00z on June 5, 1999	300 mb DIFAX upper-air map at 00z on June 5, 1999	500 mb DIFAX upper-air map at 00z on June 5, 1999

700 mb DIFAX upper-air map at 00z on June 5, 1999	850 mb DIFAX upper-air map at 00z on June 5, 1999

The upper-level flow above the surface fostered the development of a strong surface low pressure over northeastern Colorado, which wrapped copious moisture westward into southwestern and central South Dakota. This is evident in the RUC surface analysis (below left) by the high dewpoints (shaded) that were in the upper 60s and lower 70s in this area. The copious surface moisture, combined with the relatively cool atmosphere aloft, created a locally very unstable atmosphere (below right).  Lifted Indices of less than –10 C were present over the area, with CAPE of 2500 to 3000 J/kg. The most severe storms formed and moved mostly along the instability axis that extended from southwestern South Dakota to south-central South Dakota.

RUC surface MSLP, dewpoint, and wind analysis valid at 00z on June 5, 1999	RUC lifted index and surface wind analysis valid at 00z on June 5, 1999

The visible satellite image and surface observation composite at 23z (5 pm MDT) shows the relationship between the position of the thunderstorms that were forming in northwestern Nebraska to the surface features (below left). As can be inferred from the surface analyses above, and the observations in the image below, an area of convergence was present along the moisture gradient north of the axis of highest dewpoints in western South Dakota. A well-defined line of cumulus (as well as the thunderstorms that later became the Oglala storm) was oriented along this region of convergence (moisture gradient), which extended from south of Douglas, WY, northeastward to north of Aberdeen, SD. Note also the position of the surface low pressure (MSLP contoured in white) south of the tornadic storms. This is a common orientation for northern plains tornadic events. You may also want to check out the DIFAX surface chart at 00Z (below right).

Visible satellite, surface observations, and MSLP at 5 pm MDT (23z) on June 4, 1999	Surface map at 6 pm MDT on June 4th (00z on the 5th)

The aspect of the vertical profile of the wind (wind shear) is critical in determining what types of storms will form on a given day. During the evening of June 4th, there was strong wind shear between the surface and 6 km AGL, with values of 44 to 50 m/s (as demonstrated by the hodographs from the Rapid City balloon information, and the Merriman, NE, profiler). In addition to the strong shear, the storm-relative helicity was high in both wind profiles, ranging from 125 to nearly 500 m2/s2.

Sounding for Rapid City at 6 pm MDT 4 June 1999 (00z the 5th)	Hodograph for Rapid City at 6 pm MDT 4 June 1999 (00z the 5th)	Hodograph for Merriman, NE, at 6 pm MDT 4 June 1999 (00z the 5th)