Early February cold snap: Temperatures dropped to 15 to 30 degrees below zero by the morning of February 1 as cold Arctic air moved over the northern Plains. Gusty winds dropped wind chill values into the -30 to -50 degree range. Although several observing sites set daily record lows; including Hot Springs (-28), Oral (-27), and Devils Tower (-31), other stations did not reach daily record lows which were established during the region’s most extreme cold spells.
February snowfall records set: Several locations set record snowfall for the month of February, including Camp Crook whose 23 inches exceeded the previous record of 19 inches in 2007 and Long Valley with 24.9 inches, surpassing 20 inches in 1987. Both Rapid City weather stations recorded the second highest February snowfall and missed the monthly records by less than an inch. The Rapid City Regional Airport received 22.9 inches of snow, which is 16.6 inches above the normal snowfall of 6.3 inches. The record February snowfall is 23.7 inches in 1953. Downtown Rapid City’s 21.5 inches of snow is 15.2 inches above the normal snowfall of 6.3 inches. The record February snowfall is 22.0 inches set in 2001. Several other observing sites on the South Dakota plains recorded their second snowiest February: Bison had 21.8 inches, Dupree had 22.5 inches, Badlands received 17 inches, Mount Rushmore measured 19.4 inches, and Newell had 14 inches.
Early spring flooding: After a few days of unseasonably warm temperatures in early March, ice began breaking up along the White River on March 12, resulting in ice jams that lasted for more than a week from Interior to the Missouri River. Ice jams also occurred along the Belle Fourche River through Meade County and the Cheyenne River from near Elm Springs to Bridger, Cherry Creek, and Lake Oahe March 12-15. Rapidly-melting snow caused the first round of spring flooding along the Little Missouri River, Moreau River, and South Fork of the Moreau River in northwestern South Dakota in mid-March.
Damaging winds: Winds reached 35 to 55 mph with gusts near 80 mph on April 30. The winds blew over several trucks on northwestern South Dakota highways and toppled the large iconic sign for a rally campground near Sturgis.
Record annual snowfall: The winter of 2010-2011 was one of the snowiest winters in northwestern and west central South Dakota. Dupree and the Badlands National Park both set yearly snowfall records. Dupree’s 97.0 inches surpassed the previous record of 81.5 inches set in 1949-50. Badlands measured 66.0 inches; the previous record was 57.9 inches that fell in 1956-57. Both Bison and Camp Crook had the second highest yearly snowfall, measuring 67.3 inches and 100.4 inches, respectively; although well behind the records set just two years ago in 2008-09 (87.9 and 133 inches, respectively).
Heavy rain and flooding in May: Several large storm systems produced very heavy rain over the northern Plains in the month of May, which lead to flooding along the Missouri River through the summer. A single thunderstorm dropped as much as four inches of rain in an hour over Newcastle; flooding streets and basements. In the Black Hills region, two to four inches of rain fell May 19 and 20, with the heaviest precipitation along the eastern slopes of the Black Hills. The higher elevations of the Black Hills received several inches of snow with as much as a foot of snow reported in the Deerfield area. On May 21 and 22, another slow moving storm brought an additional one to two inches of rain to northeastern Wyoming, the northern Black Hills, and western Butte and Harding Counties. Two to 3.5 inches of rain fell across the Bear Lodge Mountains and the northern foothills. A third storm May 29-30 produced one to 1.5 inches of rain across a large area of northeastern Wyoming, the Black Hills, and southwestern South Dakota, with 1.5 to 2.5 inches of rain falling over the eastern foothills.
By the end of May, normally the region’s wettest month of the year, rainfall across northeastern Wyoming and western South Dakota totaled 150 to 300 percent of normal. Newcastle set both May and all-time monthly records, with 8.29 inches exceeding 6.00 inches that fell in May 1991 and surpassing 6.35 inches in June 1999. Camp Crook measured 7.26 inches, which broke the previous May record of 6.93 in May 1982 and monthly record of 7.18 inches that fell in June 1941.
May 2011 precipitation amounts over the northern Plains
May 2011 percentage of normal precipitation over the northern Plains
The rain caused widespread flooding across much of western South Dakota, especially Lawrence, Butte, and Harding Counties; and Crook and Weston Counties in northeastern Wyoming. Record flooding occurred along the Little Missouri River in western Harding County. The river gauge at Camp Crook measured a crest of 19.27 feet, which is 7.27 feet above flood stage, and exceeding the previous record crest of 17.67 feet set in 2009.
Warmer & humid summer: Downtown Rapid City’s high temperature hit 101 degrees on June 29—the first time since 2007 that triple-digit temperatures were recorded in June. The Rapid City airport reached the century mark on July 18. Residents of our relatively-dry region also had to deal with higher humidity levels. Typical summer dewpoints, which is a measure of water vapor independent of the air temperature, are in the 50s, with an average of 55 degrees in July. July 2011 had a mean dewpoint of 60.5 degrees and dewpoints often near 70, more common in eastern South Dakota.
Mild tornado season: Seven tornadoes were reported in 2011; four of them caused damage.
The severe weather season started with three tornadoes during the evening of May 9. One tornado caused minor damage at a ranch north of Philip and was rated an EF-1 on the Enhanced Fujita Scale. Another tornado was reported shortly afterward near Ottumwa, but no damage was noted in this area. Later that night, a third tornado crumpled a large electrical transmission tower and snapped trees northeast of Wall. Winds were estimated at 115 to 130 mph, which classified this tornado as an EF-2.
A tornado destroyed part of a barn, rolled large steel calf shelters, blew down steel stockade walls, and lifted a calf shelter over a nine foot fence west of Redig in southern Harding County on June 12.
A very small tornado touched down briefly near Okreek in northeastern Todd County on June 14.
Many people viewed a small tornado southwest of Newell on July 1, but it caused no damage.
A large tornado tracked over the Slim Buttes in eastern Harding County on July 18, dissipating before it reached SD Highway 79 south of Reva. It blew over a semi-trailer and several large trees and caused minor damage to buildings when it first touched down west of the Slim Buttes.
Wild hail season: The National Weather Service office received 316 reports of hail 1" diameter or larger. The largest hail stone reported was the size of a softball (4 ¼") near Camp Crook in western Harding County on July 22, when a series of thunderstorms dropped large hail across the county. Four storms produced hail three inches in diameter (larger than a baseball). Large hail damaged cars and buildings throughout the Black Hills during the summer: Hill City on June 25, Upton on July 2, Custer on July 7, Pactola on July 25, and Spearfish on July 31.
Rapid City was pounded by large hail six times. On April 21, penny-sized hail blanketed the east side of town. A barrage of three inch diameter hail and 70 mph winds damaged buildings, vehicles, and trees on the west side of town on June 24. Quarter-sized hail fell again over parts of Rapid City area the two days. Ping-pong ball sized hail and 70 mph wind gusts caused extensive damage on the south side of town on July 27. Golf ball sized hail fell across Rapid City August 7. The final storm dropped half-dollar sized hail across the east side of town on September 1. The city Growth Management office issued over 2,000 building permits for residential roof repairs with an estimated cost of more than 13 million dollars. Another victim was the large concrete Apatosaurus dinosaur statue on Skyline Drive, whose paint was chipped by the hail stones.
Thunderstorms generated 275 reports of wind gusts 60 mph or higher with 23 reports of hurricane force (75 mph) or higher gusts. The strongest wind was a 94 mph gust measured by the automated station at the Lemmon Airport on July 31. Wind gusts uprooted about 100 trees at Devils Tower National Monument June 12. A thunderstorm downed large trees and fences in Sundance the night of July 8. Microburst winds tore the roof off a shed and tossed it into a nearby hotel in Wall on July 21.
Lightning ignites wildfires: The Whoop Up fire east of Newcastle near the South Dakota state line began July 18 and grew to more than 10,000 acres due to hot and dry conditions. Lightning ignited the Coal Canyon fire north of Edgemont on August 11, which burned over 5,000 acres. The Rourke fire north of Gillette covered more than 4,000 acres after it started August 22.
Warm fall days: Temperatures heated up into the upper 80s and 90s on October 1-3, setting records at many sites. The Rapid City Regional Airport’s high of 96 degrees on October 2 was a new record high for the month of October, breaking the previous record of 94 degrees most recently recorded on October 1, 1995. The Rapid City NWS office’s maximum temperature was 94, five degrees above the previous record of 89 degrees set in 1997. The heat prompted the issuance of Red Flag Warnings for extreme fire danger. Several prairie fires spread quickly by gusty winds and scorched thousands of acres, including the Okreek Fire that started between Winner and Mission.
Rare October thunderstorms: Severe thunderstorms produced large hail, strong wind gusts, and even several funnel clouds on October 6. Extensive damage to trees, power poles, and outbuildings occurred in Newcastle and throughout Weston County.
November snow storm: A storm left a narrow band of heavy snow across western South Dakota November 18 and 19. The Rapid City Regional Airport set a 24 hour November snowfall record with a total of 13.8 inches, while downtown Rapid City had 10.7 inches—the second highest 24 hour November snowfall. The storm produced the bulk of the month’s snowfall total of 14.6 inches, which was the third highest November snowfall at the airport, behind 33.6 inches in 1985. The Rapid City NWS’s snowfall totaled 11.6 inches for fourth place in November snowfall.