May temperatures were cool, averaging 4 to 6 degrees below normal. All locations reported below normal temperatures. Gillette 4SE in northeast Wyoming was the warm spot, averaging 2.5 degrees below normal. Wright 12W in northeast Wyoming was the cold spot, averaging 7.6 degrees below normal.
May was a very wet month. Rainfall for the month averaged 180 to 200 percent of normal. Only Dupree 15SE and Kirley 6N reported below normal precipitation. The wettest area was across northeast Wyoming where precipitation averaged 250 to 300 percent of normal. The driest areas were across central and south central South Dakota where precipitation was 90 to 110 percent of normal. The wet spot was at Wright 12W in northeast Wyoming, where precipitation was 361 percent of normal. Dupree 15SE was the dry spot with only 65 percent of normal precipitation. The precipitation surplus for the month averaged 2.66 inches.
Snowfall was light in May. Across the Bear Lodge Mountains and northern Black Hills 1 to 3 inches of snow fell. On the plains of northeast Wyoming and northwest South Dakota snowfall was a trace to an inch, with no snow reported elsewhere on the South Dakota plains.
May storm summary...
May 9…A strong upper level disturbance brought severe thunderstorms and flooding to the region. Tornado touchdowns were reported in far northeastern Pennington County and across central Haakon County. Flash flooding was reported in Newcastle, where 4 inches of rain fell in an hour. Flash flooding was also reported in northern Meade and southern Perkins County as strong thunderstorms dropped 3 to 4 inches of rain in less than 2 hours. Large hail was reported across southern and central portions of western South Dakota. The largest hail reported was 2 inches in diameter, 3 miles northeast of Quinn in Pennington County.
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.
May 18-20…A deep, slow moving upper level low pressure system brought heavy rains to western South Dakota and northeast Wyoming. The storm dropped 1 to 2 inches of rain over the region, with 2 to 4 inches of rain falling along the eastern and northeastern foothills of the Black Hills. The heaviest rain reported was 4.00 inches, 3 miles northwest of St. Onge in Lawrence County, and 3.07 inches, 3 miles southwest of Rapid City in Pennington County. The heavy rains caused minor flooding of creeks and streams.
May 21-22…Another slow moving upper level low pressure system brought additional heavy rains to northeast Wyoming and far western South Dakota. Widespread rainfall of 1 to 2 inches fell over northeast Wyoming, the northern Black Hills and far western portions of Butte and Harding counties. The heaviest rains fell across the Bear Lodge Mountains and in the northern foothills of the Black Hills where 2.0 to 3.0 inches of rain was reported. The heaviest rain reported was at Bear Ridge in Lawrence County, where 3.35 inches of rain fell. The heavy rains produced widespread flooding of creeks and streams.
May 24…An isolated severe thunderstorm dropped 1.45 inches of rain on Upton in Weston County producing flooding of roadways in the town. The storm also dropped quarter size hail 5 miles northwest of Rozet in Campbell County.
May 29-30…An upper level low pressure system brought 1 to 1.5 inches of rain to northeast Wyoming…the Black Hills and southwest South Dakota. The heaviest rains fell along the eastern foothills of the Black Hills where 1.5 to 2.5 inches of rain fell. The heaviest rain reported was 2.58 inches 7 miles southwest of Rapid City in Pennington County. The heavy rains produced minor flooding of creeks and streams.
|LOCAL EXTREMES||Rapid City||Lead||Gillette|
|Max. Temp.||76 degrees||8th||67 degrees||8th, 9th||75 degrees||8th|
|Min. Temp.||27 degrees||3rd||26 degrees||2nd, 14th||23 degrees||2nd|
|Precipitation||5.88 inches||7.33 inches||7.04 inches|
|Snowfall||Trace||3.0 inches||0.0 inches|
|Max. Precipitation||2.05 inches||19th||1.39 inches||22nd||1.55 inches||10th|
|Max. Snowfall||Trace||14th||2.0 inches||14th||0.0 inches|
|REGIONAL EXTREMES||Western South Dakota||Northeast Wyoming|
|Max. Temp.||89 degrees||Cedar Butte 1NE||9th||76 degrees||Devils Tower||9th|
|89 degrees||Midland||8th||76 degrees||Dillinger||8th|
|Min. Temp.||17 degrees||Lodgepole 5SW||2nd||18 degrees||Upton 14ENE||2nd|
|Precipitation||Western South Dakota||Northeast Wyoming|
|Max. Precipitation||9.34 inches||Fort Meade||8.29 inches||Newcastle|
|Min. Precipitation||1.96 inches||Dupree 15SE||5.29 inches||Weston 1E|
|Max. Snowfall||3.7 inches||Custer||1.5 inches||Upton 14ENE|
|Min. Snowfall||0.0 inches||0.0 inches|
|Max. Precipitation||2.75 inches||Bear Ridge||22nd||2.87 inches||Hulett||22nd|
|Max. Snowfall||3.7 inches||Custer||19th||1.1 inches||Sundance||1st|
|MONTHLY RECORDS||WESTERN SOUTH DAKOTA AND NORTHEASTERN WYOMING|
|LOCATION||DATE||NEW RECORD||OLD RECORD||DATE|
|Camp Crook||May||7.26 inches precipitation||6.93 inches precipitation||1982|
|Devils Tower, WY||05/22/2011||2.50 inches precipitation||2.27 inches precipitation||05/06/2007|
|Newcastle, WY||05/10/2011||2.76 inches precipitation||2.34 inches precipitation||05/26/1929|
|Newcastle, WY||May||8.29 inches precipitation||6.00 inches precipitation||1991|
|Winner||May||53.7 degree avg. temperature||54.2 degree avg. temperature||2008|
|Wood||May||52.3 degree avg. temperature||52.4 degree avg. temperature||2002|