December 20, 2017
Rapid City Weather Forecast Office
RAPID CITY, SD – Winter storm tracks in early 2017 favored southern South Dakota, while areas farther north were much drier. Eight to 15 inches of snow were reported from Oglala Lakota County eastward to Tripp County on January 24-25 while the Black Hills received only three to eight inches. Another storm left four to eight inches of snow, with localized amounts near 12 inches, over parts of northeastern Wyoming, the eastern slopes of the Black Hills and across far southern South Dakota on February 23-24. The final winter storm on April 9-10 produced four to eight inches of snow over northern Campbell County, the Bear Lodge Mountains, and the Black Hills while a small swath of four to twelve inches of snow fell across parts of Jackson, Mellette, and northern Tripp Counties.
Precipitation amounts varied across the region during the rest of the winter into early spring with only a small area of abnormally dry conditions noted over northeastern Wyoming by the beginning of May. However, just over 50% of average precipitation during May—normally the wettest month of the year—led to a rapid intensification of drought conditions. Much below normal rainfall continued through the summer. By early July, the entire area was at least abnormally dry with severe drought covering much of northwestern South Dakota and areas of extreme drought persisting east of the Black Hills through the rest of the year.
The dry conditions also contributed to a rather mild severe weather season. The Rapid City NWS office issued only 183 severe thunderstorm warnings—the fewest number since 1996 (the previous lowest was 187 warnings in 2002). Some of the significant storms during the summer included:
A band of severe thunderstorms spawned several tornadoes over eastern Wyoming and the Nebraska panhandle on June 12. Although the storms weakened by the time they reached South Dakota, quarter sized hail and 70 mph wind gusts were reported, and a small tornado was spotted southwest of Allen but caused no damage. The straight line winds blew over a semitrailer on Interstate 90 near Kadoka.
A wind storm with gusts to 75 mph swept across southwestern South Dakota on June 27. The Custer County Airport station recorded a peak gust of 69 mph, which is the highest gust ever recorded at that site. The Custer YMCA building lost a section of its roof, several signs were blown over and broken, and numerous trees were blown down.
The strongest storm of the season pounded the Newell area with baseball sized hail and wind gusts over 90 mph on July 18. Several sheds and numerous trees were toppled, building and car windows were broken, and crops destroyed.
One of the most active thunderstorm days was August 14 when severe thunderstorms tracked from the northern Black Hills over Rapid City. Large hail damaged roofs and heavy rain caused localized street flooding on the north side of town. Later in the evening, stationary thunderstorms dropped baseball sized hail and two to four inches of rain over northern Oglala Lakota County, causing flash flooding along Porcupine Creek from Rockyford to Porcupine. A family took shelter in a church and was stranded overnight before being rescued.
Three to five inches of rain fell during the morning of August 25 across southern Ziebach County. Runoff caused flash flooding along Ash and Rattlesnake Creeks and water ran over several county and BIA roads.
The second of only two tornadoes for the year touched down on August 26. The brief rope tornado damaged some trees south of Oelrichs near the Nebraska border.
The 2017-18 winter season started with strong winds. Both Rapid City Regional Airport and the downtown NWS office recorded 50 mph wind gusts on eight days between December 4 and 14. The winds continued during the nighttime hours and contributed to the rapid spread of the Legion Lake Fire in Custer State Park on December 11-15.