2011 Annual Climatic and Hydrologic Summary for
Western South Dakota and Northeastern Wyoming

Temperature and Precipitation Summary

Temperatures averaged 0.5 degrees above normal across the entire region for the year. For the first 6 months of 2011, temperatures were well below average, with February 6.5 degrees below average, and May 4.4 degrees below average. The second half of the year was much warmer, with October 3.4 degrees above average, and December 5.1 degrees above average. Gillette 4SE in northeast Wyoming was the warmest location, averaging 2.0 degrees above normal for the year. The coolest location was Winner, where temperatures averaged 2.2 degrees below normal.

Precipitation averaged 118 percent of normal across the entire region, with the average surplus being 3.33 inches. Most locations received well above average precipitation from January through August, with January, February, and May averaging around 200 percent. The highest precipitation total was at Lead, where 34.44 inches of precipitation fell. Colony was the driest location, with only 14.45 inches. The wettest locations by percentage were Hermosa 3SSW and Hoover, receiving 143 percent of normal precipitation. The driest location by percentage was Edgemont, receiving only 85 percent of their yearly average precipitation. Newcastle set both May and all-time monthly records, with 8.29 inches of rainfall that month. This exceeded the 6.00 inches that fell in May of 1991, and surpassed the 6.35 inches of precipitation that fell in June of 1999. Camp Crook measured 7.26 inches, which broke the previous May record of 6.93 in May 1982, and their all-time monthly record of 7.18 inches that fell in June of 1941.

Snowfall averaged 150 percent of normal across the entire region, with the average surplus being 20 inches. The snowiest months were January and February, with most locations receiving 250 to 300 percent of their normal snowfall totals. March and April snowfall was also above average for most locations. With the warmer and drier conditions in the Fall and early Winter, snowfall averaged slightly below average for November and December. The highest snowfall total was at Lead, where 164 inches fell. Colony had the least amount of snow, with only 39 inches for the year. The snowiest location by percentage was Ludlow 3SSE, receiving 356 percent of normal snowfall. The least snowiest location by percentage was Gillette 4SE, receiving only 72 percent of their average yearly snowfall.

Click here for 2011 precipitation totals

Significant storms of 2011

Snowstorms of 2011

The first significant snowfall of 2011 occurred on January 8, when 6 to 12 inches of snow fell on the northern Black Hills and Bear Lodge Mountains, with 3 to 6 inches on the plains of northeast Wyoming and western South Dakota. Two weeks later on January 22, an upper level disturbance brought 4 to 9 inches of snow to the northern Black Hills and Bear Lodge Mountains.
 
A series of upper level disturbances moved across the region on February 5 through 7, bringing 18 to 24 inches of snow to the northern Black Hills and Bear Lodge Mountains, with only light snowfall amounts on the plains. Two weeks later on February 19 and 20, a strong upper level disturbance brought 10 to 18 inches of snow to northwest and central South Dakota. Elsewhere on the South Dakota plains 5 to 10 inches of snow fell. A few day later, on February 23-24, a strong upper level storm system brought 8 to 12 inches of snow to the southern and central Black Hills, southwest South Dakota and across Weston County in northeast Wyoming. Across the west central and south central plains of South Dakota, 4 to 8 inches of snow fell.
 
March was a quiet month with only one significant snowfall. On March 26, a strong upper level disturbance brought 4 to 8 inches of snow to northwest South Dakota.
 
A strong storm system moved across the central Plains on April 14, dropping 6 to 12 inches of snow across south central South Dakota. Elsewhere on the plains of western South Dakota, 3 to 6 inches of snow fell. A few days later on April 19, an upper level storm system brought 3 to 7 inches of snow to northwest South Dakota. On April 22,
a strong upper level disturbance brought 6 to 12 inches of snow to the northern Black Hills and Bear Lodge Mountains.  A few days later on April 26, an upper level disturbance moved across the region and brought 4 to 6 inches of snow to the higher elevations of the northern Black Hills and Bear Lodge Mountains.
 
A very strong winter storm crossed the area late on November 18th and through the 19th, dropping significant snow across much of the area. Snowfall amounts ranged from 10 to 20 inches across most parts of northeast Wyoming and the Black Hills, with a narrow strip of 4 to 8 inches of snow falling across eastern Pennington and Haakon counties.
 
Upslope enhanced snowfall occurred over the northern Black Hills into the Bear Lodge Mountains late in the evening on November 30th and continued into December 1st,  bringing multiple reports of over 6” snowfall.   The heaviest snow was in the Deadwood area, where 11” was reported. 

2011 Convective Weather 

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. 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 Reservoir on July 25, and Spearfish on July 31.
 
Rapid City was pounded by large hail several times. 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. 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.
 
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.
 
A rare, late season convective system brought severe weather to the area in early October. Several thunderstorms produced large hail, strong wind gusts, and even several funnel clouds on the 6th. Extensive damage to trees, power poles, and outbuildings occurred in Newcastle and throughout Weston County.
 
Seven tornadoes were reported in 2011, with four of them causing damage.
 
Three tornadoes occurred on 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 area 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 Slim Buttes. 

Windstorms of 2011 

A strong cold front moved across the region on March 11, bringing northwest winds of 35 to 45 mph with gusts in excess of 60 mph to northeast Wyoming and western South Dakota. The strongest wind gust in northeast Wyoming was 76 mph, 2 miles northeast of Echeta in Campbell County. In South Dakota the strongest wind gust was 71 mph, 5 miles west of Spearfish.
 
A strong upper level disturbance moved across the region on April 22, bringing strong northwest winds to southwest and south central South Dakota. Sustained winds of 30 to 40 mph with gusts in excess of 60 mph were common across southwest and south central South Dakota. The strongest wind gusts reported were 70 mph, 2 miles east of Okreek, and 64 mph, 6 miles west of Parmelee, both in Todd County.
 
A deep low pressure system moved across the region on April 30, bringing strong northwest winds of 35 to 45 mph with gusts in excess of 65 mph to western South Dakota and northeast Wyoming. The strongest wind gust across northeast Wyoming was 70 mph, 2 miles southeast of Colony in Crook County. Across western South Dakota winds gusted to 82 mph at Buffalo, 76 mph at Newell, and 75 mph at Faith and Wall.
 
On May 16 a tight pressure gradient produced southeast winds of 35 to 45 mph with gusts to around 60 mph across northeast Wyoming and far northwestern South Dakota. Winds gusted to 65 mph, 25 miles north of Weston in Campbell County, and to 59 mph at Buffalo in Harding County.
 
A very strong cold front moved through the northern plains the evening of September 19th and the early morning hours of the 20th. Wind gusts of 50 to 70 mph were common across much of the area. 

2011 Flooding Summary 

January began as usual with no flooding being reported. However, a brief January thaw at the end of the month caused some slight ponding of water near normally dry creeks and in low lying areas.
 
In February, snowmelt and ice jams caused flooding in western South Dakota. On February 14th, snowmelt and ice jams caused flooding along White Clay Creek, Wounded Knee Creek and Porcupine Creek in Shannon County. Several unnamed BIA roads were flooded and 6” of water was reported over a section of Highway 18 about 5 miles east of Oglala at White Clay Creek. In Bennett County, Spring Creek, Bear Creek, Bear in the Lodge Creek caused flooding across a few county roads due to overwhelmed culverts. The flooding in Shannon and Bennett Counties lasted until February 17th.
 
A February thaw created ice jam flooding on the White River. On February 15, an ice jam formed about two miles upstream from the Highway 44 Bridge near Interior. The ice was 6” to 8” thick and caused flooding of pasture land near the river. Downstream the ice jam caused minor to moderate flooding at the White River near the Highway 83 Bridge and at the Highway 47 Bridge south of Reliance. Ice jam flooding continued along the White River near Oacoma into early March. Minor flooding occurred, but cold air moved back into the area, allowing the flooding to subside by March 4.
 
As warmer weather made a return by mid-March, so did the flooding. Minor flooding was reported along the Little Missouri River, Little White River, and the Belle Fourche River, while moderate flooding was reported along the Moreau River, Cheyenne River and White River.
 
On the Belle Fourche River, ice jams combined with snowmelt runoff caused flooding problems. On March 12 two ice jams were reported on the Belle Fourche River. The first ice jam was located at the Highway 34 Bridge about 20 miles east of Sturgis. This ice jam caused minor flooding along the river from about 5 miles upstream to about 10 miles downstream as the water backed up behind the jam, released and reformed downstream. The second ice jam was located in eastern Meade County near the confluence of the Belle Fourche and Cheyenne Rivers. Several feet of water backed up behind this jam and caused minor flooding.
 
On the Cheyenne River, releases began from Angostura Reservoir in February. By mid-month, ice breakup along the river was in full-swing. By March 12, several ice jams along the Cheyenne River caused flooding. A ranch in Meade County was surrounded by water due to an ice jam near the Meade/Pennington County line. Another ice jam was reported downstream near the Highway 34/73 Bridge. This ice jam, and possibly others, caused moderate flooding at the Highway Bridge upstream to the confluence of the Belle Fourche River.
 
On the White River, flooding was reported near Interior to the confluence with the Missouri River. Several ice jams formed, released and redeveloped between March 13 and March 18. At least three homes were reported to be surrounded by water. One home was located south of the Badlands, another was south of Belvidere and another was near the Highway 47 Bridge. Several other homes and ranches may have been impacted, but the NWS did not receive any other damage reports.
 
In Harding County, flooding of small creeks and streams caused minor flooding of County Roads in mid-March. On the Little Missouri River, flooding of agricultural land was reported from March 16 to March 23 extending from the Montana Border to Camp Crook. Also an ice jam south of the North Dakota/South Dakota Border caused flooding of a County Road west of Ladner along the Little Missouri River.
 
In Perkins, Ziebach and northeastern Butte Counties, flooding was reported on Rabbit Creek, the Moreau River, Thunder Butte Creek and the Grand River beginning on March 16. Eight to ten roads were closed in Perkins and Ziebach Counties due to the flooding. Releases from Shadehill Reservoir peaked at 3,500 cfs around March 21st. At the end of the month, flooding on most of the creeks and streams subsided. However, a few crossings downstream from
Shadehill remain flooded due to releases of 1350 cfs or so from Shadehill Reservoir. Flows on the Grand River above 600 cfs will cause flooding of downstream river crossings.
 
The flooding subsided for the month of April, but on May 9 in Newcastle, three to four inches of rain and hail fell in a little over an hour. This rain and hail caused flooding that overwhelmed the drainage system and caused significant damage. Damage from the flooding was mainly water in basement and washed out driveways, however some infrastructure damage (foot bridges) in a local park also occurred.
 
By the middle of May, a significant weather pattern shift occurred. During this time several, slow-moving, upper level disturbances moved through the area. These disturbances produced very heavy rainfall that caused flooding and flash flooding across portions of northeastern Wyoming and western South Dakota. Several counties in western South Dakota experienced significant flooding, especially Butte County, which had a no unnecessary travel advisory in affect for several days. The Little Missouri River at Camp Crook crested at a new record. The preliminary record crest is a gage height of 19.27 ft and 19,400 cfs on May 24. The previous record was 17.67 ft and 12,400 cfs in 2009. According to residents, water was in homes that were built before 1900 that have never had water in them before. Also the water threatened Highway 20 between Camp Crook and Buffalo.
 
On May 24, heavy rain caused flash flooding in Upton. Water was reported flowing down Main Street and Highway 16 due to runoff from the heavy rain. The official rainfall amount in Upton was 1.79 inches, but most of this rain fell in about an hour.
 
Flooding from the widespread heavy rain between May 21 and the end of the month was reported along the Belle Fourche River, Cheyenne River, Grand River, Elk Creek, Horse Creek, Rapid Creek, Horse Creek and Battle Creek. Counties with flooding included Crook and Weston Counties in northeastern Wyoming and Harding, Butte, Lawrence, Meade, Pennington, Custer, Fall River, Perkins, Haakon, Ziebach, and Jackson Counties in western South Dakota.
 
On June 11, one to two inches of rain and hail fell in an hour over southwestern South Dakota. Minor flooding of County Road 3 was reported in southeastern Fall River County. A slow moving thunderstorm during the evening of June 16 produced 2.4 inches of rain southeast of St. Francis. Runoff from this heavy rain damaged roads and left fence posts hanging in the air.
 
By the middle of June, a slow moving upper level storm system moved across the Rockies into the northern plains. This storm system produced widespread heavy precipitation across south central South Dakota on June 20-21. Precipitation amounts up to five inches were reported that flooded some basements. Many secondary roads in in Todd, Tripp, Mellette, Bennett and Jackson Counties had washouts due to flooding as well as water flowing over the roads.
 
Significant flooding occurred over the weekend of June 24-26 due to runoff from heavy rain. One complex of storms washed out roads and flooded ranches in the Midland area of central South Dakota. This storm also caused flooding on Ash Creek and Brave Bull Creek and caused a stock dam to fail and flood Highway 63 for up to 300 ft. The excessive rainfall and runoff also caused flash flooding in south central Meade County where a few County Roads were flooded and gravel was washed off roads in spots. In Hot Springs, the dip bridge at South 6th Street quickly flooded for fifteen minutes. In Rapid City, several streets had water running across them as the hail and rain overwhelmed the storm drains.
 
On July 1, early afternoon thunderstorms developed over western South Dakota. Runoff from heavy rainfall caused street flooding in Belle Fourche. The next day on July 2, early afternoon thunderstorms produced heavy rain over portions of northeastern Wyoming. Two to three inches of rain fell across portions of Crook County causing minor flooding along Cabin Creek and other small creeks and streams in central Crook County.
 
During the morning hours of July 7, one to three inches of rain fell in less than an hour over southern Perkins County. Runoff from heavy rainfall caused gravel and debris to be washed over Moreau River Road about five miles west northwest of Bixby. Brushy Creek and other small creeks and streams also had minor flooding. Later in the afternoon on the 7th, runoff from heavy rain caused flooding along Potato Creek just south of Potato Creek and water was reported running over stock dams in the same area.
 
On July 18, afternoon thunderstorms with heavy rain in northwestern South Dakota caused street flooding in Buffalo.
 
On July 22, an area of low pressure pushed through western South Dakota. Ahead of this system, abundant moisture was in place. A few of the stronger afternoon and evening thunderstorms produced flooding. Street flooding was reported in Rosebud, Faith, and Buffalo when one to two inches of rain fell in 30 minutes. In Harding County, runoff from heavy rain caused rural roads along Highway 85 north of Buffalo to become quickly inundated with water. Several roads, culverts and driveways were damaged by the flooding.
 

During the beginning of August, minor flooding occurred across northeastern Wyoming and western South Dakota. On the 3rd, two inches of heavy rain in less than an hour caused small stream flooding southeast of Keyhole Reservoir. On the 5th, minor street flooding occurred in Hermosa when small hail combined with an inch of rain fell in 15 minutes. On the 7th, minor street flooding occurred in Hermosa, Rapid City and Rapid Valley when storm drains became overwhelmed by a quick inch of heavy rain. As these storms moved east, runoff from heavy rain caused minor flooding around Red Shirt, along Highway 44 near Caputa and Farmingdale, and on Highway 40 southeast of Hermosa. By the middle of August, the area began to dry out and no reports of flooding were received for the rest of 2011.

2011 Temperature Extremes

Station
High
Date(s)
Low
Date
Buffalo*
97
June 29
-21
February 25
Cottonwood
106
July 18, Aug 2
-21
January 12
Faith
102
July 19
-18
February 2, 8
Gillette
104
July 19
-23
February 1
Interior
103
June 17, 18, 19, 20
-17
January 12
Pine Ridge *
104
August 23
-21
February 2
Philip *
105
July 19
-19
January 12
Rapid City Airport *
102
July 19
-20
February 2
Winner
103
July 20
-10
January 12

2011 Precipitation Extremes

Station
Rainfall
Date(s)
Snowfall
Date(s)
Buffalo *
1.74
May 19
Not Available
Not Available
Cottonwood
1.35
Ma7 20
7.0
February 20
Faith
1.20
July 26
14.0
February 20
Gillette
1.55
May 10
5.5
January 9
Interior
1.38
June 26
9.0
February 21
Pine Ridge *
1.63
May 19
Not Available
Not Available
Philip *
1.36
May 24
Not Available
Not Available
Rapid City Airport
2.05
May 19
9.7
February 20
Winner
3.24
June 21
9.0
April 15

* Data is from the automated weather station

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