May 2010 Climatic Summary

May temperatures were cold, averaging 2 to 4 degrees below normal. All locations reported below normal temperatures. Spearfish was the warm spot, averaging 1.4 degrees below normal. The cold spot was at Wright 12W in northeast Wyoming,  where temperatures averaged 6.9 degrees below normal.
Precipitation in May average 30 to 50 percent above normal. The wettest areas were across northeast Wyoming and northwest South Dakota where precipitation averaged 150 to 200 percent of normal. The driest areas were across south central South Dakota where precipitation was 50 to 75 percent of normal. The wet spot was at Maurine 10 SW where precipitation was 220 percent of normal. Mission was the dry spot with only 45 percent of normal precipitation. The precipitation surplus for the month averaged 1.28 inches.
Snowfall in May was well above normal. Across the northern Black Hills and Bear Lodge Mountains 1 to 3 feet of snow fell. Elsewhere, on the plains of northeastern Wyoming 2 to 6 inches of snow fell, with most areas on the plains of western South Dakota receiving 4 inches or less.

May Storm Summary...

On May 1…An upper level storm system brought 6 to 12 inches of snow to elevations above 5500 feet in the northern Black Hills and Bear Lodge Mountains.

On May 4…A deep low pressure system in North Dakota produced a strong pressure gradient across western South Dakota. Strong northwest winds of 35 to 45 mph with gusts in excess of 60 mph were common. The strongest wind gusts reported were 76 mph at Buffalo and 70 mph, 23 miles northeast of Newell.

On May 5 and 6…An upper level storm system brought 4 to 8 inches of snow to far northwest South Dakota, the Bear Lodge Mountains and far northern Campbell and Crook counties in northeast Wyoming.

On May 10 through 12…A slow moving upper level trough brought heavy rain and snow to the region. During the three days 10 to 18 inches of snow fell above 5500 feet in the Black Hills with 4 to 10 inches falling below 5500 feet. Snowfall of 1 to 4 inches fell on the plains of northeast Wyoming and southwest South Dakota. Rainfall totals of 1.5 to 3.3 inches were common across the region with the heaviest total along the northern and eastern foothills. Minor flooding occurred along the Belle Fourche river in Crook County in northeast Wyoming.

On May 18…An isolated thunderstorm dropped nearly 4 inches of rain in less than three hours over Crook County in northeast Wyoming. Flash flooding was reported along Oak Creek, Hay Creek and Beaver Creek. Oak Creek Road and Mona Road were severely damaged. At one crossing, during the worst part of the flooding, the water was at least 3 feet above the road and was over 30 feet deep around 630 PM. There was a lot of debris and the water cut away at the road base at all of the culverts in the area.

On May 21…Scattered thunderstorms brought heavy rain and large hail to portions of western South Dakota. Quarter size hail was reported across Fall River and Ziebach counties. Heavy rains produced minor flooding along small streams and creeks in Ziebach, Shannon, Custer and Pennington counties.

On May 22…Scattered thunderstorms brought large hail to central and south central South Dakota. There were several reports of nickel to quarter size hail. The largest hail reported was the size of golf balls 2 miles southeast of Winner in Tripp County.

On May 24…A strong low pressure system moved across the area producing tornadoes, large hail, damaging winds and widespread flash flooding. Tornadoes were reported 3 miles southeast of Plainview and 8 miles southwest of Faith in Meade County, and 6 miles northeast of Chance in Perkins county. The tornado in Perkins county destroyed a school and heavily damaged a ranch. There were also numerous reports of winds gusts of 60 to 70 mph. The strongest wind gust was 70 mph, 8 miles northwest of Usta in Perkins County. The thunderstorms produced heavy rains that caused flash flooding in Meade, Pennington, Fall River, and Custer counties. Numerous roadways were flooded with some roads being washed out. There were numerous reports of hail in excess of 1.5 inches in diameter. The largest hail reported was 4.25 inches in diameter near Maverick Junction in Fall River County and 4.00 inches in diameter 2 miles northwest of Buffalo Gap in Custer County.

On May 26…A strong upper level disturbance produced severe thunderstorms with large hail across northeast Wyoming. There were numerous reports of quarter size hail or larger. The largest hail to fall was the size of golf balls in downtown Gillette.

On May 29…A strong upper level disturbance produced severe thunderstorms with large hail and heavy rains across south central South Dakota. There were numerous reports of quarter size hail or larger. The largest hail to fall was the size of baseballs in Colome in southern Tripp County. Heavy rains of 2 to 4 inches produced minor flooding of streams and creeks in southern Tripp County.


LOCAL EXTREMES

Temperature Data

Rapid City

 

Lead

 

Gillette

 

 

Temperature

Date

Temperature

Date

Temperature 

Date

Maximum Temperature

88 degrees

28th

86 degrees

28th

82 degrees

28th

Minimum Temperature

21 degrees

8th

17 degrees

8th

18 degrees

8th

Precipitation Data

Rapid City

 

Lead

 

Gillette

 

Monthly Data

Amount

Data

Amount

Date

Amount

Date

Precipitation

5.19 inches

 

5.90 inches

 

4.82 inches

 

Snowfall

3.5 inches

 

23.0 inches

 

4.0 inches

 

 

 

 

 

 

 

 

Daily Data

 

 

 

 

 

 

Maximum Precipitation

1.81 inches

10th

1.46 inches

10th

1.10 inches

10th

Maximum Snowfall

3.1 inches

12th

7.0 inches

10th

3.0 inches

6th


REGIONAL EXTREMES

Temperature Data

 

Western South Dakota

 

 

Northeastern Wyoming

 

 

Temperature

Site

Date

Temperature

Site

Date

Maximum Temperature

94 degrees

Interior 3NE
Winner

28th, 29th
23rd

89 degrees

Newcastle

29th

Minimum Temperature

15 degrees

Mt. Rushmore

9th

16 degrees

Upton 14 ENE

8th

Precipitation Data

 

Western South Dakota

 

 

Northeastern Wyoming

 

Monthly Data

Amount

Site

Date

Amount

Site

Date

Maximum Precipitation

7.49 inches

Mt. Rushmore

 

5.60 inches

Sundance

 

Minimum Precipitation

1.63 inches

Mission

 

2.86 inches

Colony

 

Maximum Snowfall

23.0 inches

Lead

 

8.8 inches

Wright 12W

 

Minimum Snowfall

0.0 inches

Several Locations

 

0.0 inches

Several Locations

 

 

 

 

 

 

 

 

Daily Data

 

 

 

 

 

 

Maximum Precipitation

2.85 inches

Dupree

22nd

1.36 inches

Sundance

10th

Maximum Snowfall

7.0 inches

Lead
Redig 11Ne

10th
6th

5.0 inches

Wright 12W

12th


MONTHLY RECORDS

LOCATION

DATE

NEW RECORD

OLD RECORD

DATE

Devils Tower, WY

May

48.5 degree average temperature

48.6 degree average temperature

1995


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