May 2013 Climatic Summary
 
May temperatures across the entire region were very close to average for the month. The location with the coolest departure from average was Spearfish, which was -2.3 degrees below normal, while the location with the warmest departure was Gillette, at 2.2 degrees above normal.
 
Precipitation in May averaged around 150 percent of normal across the entire area.  The wettest areas were across Northeast Wyoming, the northern Black Hills and Bear Lodge Mountains, and across northwestern portions of South Dakota, where 125 to 300 percent of normal precipitation was reported. Lemmon received 9.16 inches of rainfall during the month, which was 321% of normal. The highest rainfall total for the month came from Lead, where 12.23 inches fell. The locations that missed out on the plentiful precipitation were across the southern and central Black Hills, with Mt. Rushmore receiving only 37% of normal precipitation. Snowfall for May was confined to the higher elevations of Northeast Wyoming and the Black Hills, where less than 2 inches fell.
 
May storm summary...
 
May 17th & 18th – A weak area of low pressure moved into the Northern Plains, producing some scattered thunderstorms. Dime to half dollar sized hail fell in several locations across Northeast Wyoming and western South Dakota. The strongest storms produced 2.50 inch hail near Devil’s Tower on the 17th, and 4.00 inch hail southeast of Dupree on the 18th. Some minor flooding was observed in southern Ziebach County.
 
May 19th – 21st – A vigorous slow moving low pressure system brought copious amounts of rainfall to much of the area. Three day rainfall totals for many locations ranged from an inch to over 6 inches. Upslope enhanced rainfall produced 6.51 inches of precipitation in Lead during this 3 day event.
 
May 23rd – A strong low pressure system moving out of the Northern Rockies produced very gusty southerly winds across much of Northeast Wyoming. Sustained winds of 40 to 45 mph were common, and wind gusts ranged from 55 to 80 mph in many locations.
 
May 25th – Another round of severe thunderstorms moved through Northeast Wyoming and northwestern South Dakota during the afternoon and evening hours. Quarter to golf ball sized hail fell from these storms. The strongest storms passed through Perkins County, where hail up to 3.00 inches in diameter fell.
 
May 26th – Additional severe thunderstorms developed across Northeast Wyoming during the afternoon and evening. Quarter to half dollar sized hail fell in a few locations.
 
May 27th & 28th - Another round of severe thunderstorms developed across the Black Hills area and moved across southern South Dakota. Dime to half dollar sized hail fell in many locations. Hail to the size of 2.00 inches fell near Upton in Wyoming. A brief tornado destroyed 2 mobile homes and damaged several homes in Allen, SD on the 28th.
 
May 30th – Another strong low pressure system brought 1 to 2 inches of rain to many locations. Heavy rain and some minor flooding occurred in the Rapid City area, where 4 to 7 inches of rain fell in a short period of time.
 
 
LOCAL EXTREMES
Rapid City
Lead
Gillette
Temperature
Temperature
Date
Temperature
Date
Temperature
Date
Max. Temp.
89
13th
82
13th
90
13th
Min. Temp.
31
1st
21
1st, 2nd
20
1st
Precipitation
Rapid City
Lead
Gillette
Monthly Data
Amount
Date
Amount
Date
Amount
Date
Precipitation
4.25
 
12.23
 
4.27
 
Snowfall
0.0
 
T
 
0.0
 
Daily Data
Amount
Date
Amount
Date
Amount
Date
Max. Precipitation
2.25
29th
3.55
20th
1.88
30th
Max. Snowfall
 
 
T
1st, 9th
 
 
 
 

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