The Black Hills Flood of 1972

Weather Summary

On the evening of June 9, 1972, heavy thunderstorms caused devastating flash flooding throughout Rapid City and the eastern foothills of the Black Hills; destroying homes, vehicles, businesses, bridges, and claiming 238 lives.

Surface map, June 9, 1972
Surface map on the morning of June 9, 1972.
500 mb analysis for June 9, 1972

500 millibar map for the morning of June 9,
1972 (approximately 18,000 feet above sea
 level).

Dense fog covered the eastern slopes of the Black Hills during the early morning of June 9. A large, cold high pressure system moved southward from Canada into the upper Midwest, pushing a cold front westward across the Dakotas to the eastern slopes of the Black Hills (see top map to the left). The air northeast of the front was very humid, with drier air southwest of the front. Above the ground, a ridge of high pressure extended from the Gulf of Mexico into Canada with a weak upper level disturbance over the Great Basin moving northeastward toward the northern Plains and light winds over the Black Hills area (see bottom map to the left). 
As the front moved slowly southwest during the morning, strong easterly winds brought additional moisture to the area. Dew point temperatures, a measure of the moisture in the air, were in the middle to upper 60s, about ten degrees higher than usual for early June. Upslope clouds formed over western South Dakota by the process of orographic lifting; when terrain forces air to rise, the air becomes saturated as it cools, and clouds develop (see graphic below).          

Two areas of thunderstorms developed over the

Idealized depiction of orographic lifting
Idealized depiction of orographic lifting.
Black Hills during the afternoon as the approaching disturbance made the atmosphere more unstable.  Rain over the northeastern corner of the Black Hills spread southward toward the Nemo area. Showers over the southern Black Hills and southeast of Rapid City moved northwest and intensified over the central Black Hills.  By 6 p.m., a nearly continuous line of thunderstorms covered the eastern Black Hills. The strong easterly winds along the ground and light winds above the hills kept the storms anchored in place.

The steep canyons channeled the high volumes of water that rushed toward the plains. Flood water from Deer Creek, Victoria Creek, Prairie Creek, and smaller drainages emptied into Rapid Creek above Rapid City, swelling the stream over 300 times its normal volume. Data from the stream gauge on Rapid Creek above Canyon Lake indicated that from 9:15 p.m. until 11:15 p.m., the water level rose approximately 12 feet in two hours. Flooding also occurred along Bear Butte, Elk, Box Elder, Spring, and Battle Creeks from Sturgis to Hermosa.

Around 12:30 a.m. June 10, the storms began to dissipate and move slowly to the east over the plains with no precipitation indicated by the Ellsworth Air Force Base weather radar by 6:30 a.m.

Total Storm Rainfall June 9-10, 1972

 

 

Precipitation totals (in inches) from sites 5 miles west of Rapid City, at Pactola Dam and 5 miles south-southwest of Sturgis.
Precipitation totals in inches from locations 5 miles
south-southwest of Sturgis, Pactola Dam, and near
Johnson Siding (5 miles west of Rapid City).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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