Temperature and Precipitation Summary for 2017

2017 Annual Climatic Summary for Western South Dakota and Northeastern Wyoming

Temperature and Precipitation Summary

Temperatures averaged 1.2 degrees above normal across the entire region as ENSO neutral conditions prevailed for much of the year. After a bitter cold December of 2016 - that extended into January of 2017, early spring was very warm with February and March at 5.2 and 4.7 degrees above average respectively. Temperatures were closer to average for April as cloud cover and precipitation increased. May was also near average, even though drier conditions were observed. June and July rose back above average, with July being very warm at 4.5 degrees above average. August was unsettled with temperatures 2.5 degrees below average. For the remainder of 2017, temperatures were closer to average with the exception of November at 3.4 degrees above. Much of western South Dakota and northeast Wyoming enjoyed one of the warmest Thanksgivings on record, with temperatures in the 60s and 70s for turkey day. This prolonged period of dry weather and above average temperatures late in November into early December led to a large wildfire in the Custer State Park area. The warm and dry conditions, combined with strong northwest winds, allowed the Legion Lake fire to grow more than 30,000 acres in less than a day. Mild and dry conditions persisted into the third week of December. Then, on the first full day of winter, the weather pattern finally turned much cooler.

Precipitation only averaged 80% of normal across the entire region in 2017, which was almost exactly the same percentage the area saw in 2016. Most of western South Dakota and northeastern Wyoming continued to see persistent drought conditions for much of 2017. During the early portion of the year, precipitation averaged slightly above average. But slightly above average precipitation during January and February typically does not alleviate drought conditions due to the fact that minimal precipitation falls during the winter season on average. January typically only averages 0.5 inches across the area, and February averages 0.6 inches.

After slightly above average precipitation in January and February, the next three months were well below average, with only April near average. March and May were both less than 60% of average. The lack of appreciable precipitation continued into June (70%) and July (60%), which pushed much of the area into moderate to severe drought. A few areas across the South Dakota plains entered extreme drought by the end of July. Thankfully, the rains returned in August and September, along with cooler temperatures, helping to temper the growing threat for large wildfires in the early fall period. The later fall months were drier again, with precipitation around 50-60% of average in October and November. The first half of December continued to be dry, but an active weather pattern returned to the area on the first full day of winter and continued through the end of the month. Precipitation ended up being slightly above average for December.

The highest annual precipitation total for the area was observed at Mount Rushmore, where 22.12 inches of precipitation fell. The Sundance, Wyoming station received the most precipitation by percentage, at 119% above average. Bison, South Dakota was the driest location, with 9.49 inches. They also were the driest location by percentage, receiving only 55 percent of their yearly average precipitation.

Yearly snowfall averaged 97% of normal across the entire region. January, February, and December were all above average. January and December were the snowiest, with the average surplus around 3 to 4 inches. The highest annual snowfall total was at Wright, Wyoming, where 80.5 inches fell. Lemmon had the least amount of snow, with 21.0 inches for the year. The snowiest locations by percentage were Interior, receiving 179% of normal snowfall. Lead received the least amount of snow by percentage at only 42% of their average yearly snowfall.

2017 Temperature Extremes

2017 Precipitation Extremes

* Data is from the automated weather station where snowfall amounts are not available.

2017 Notable Weather Events

Winter storm tracks in early 2017 favored southern South Dakota, while areas farther north were much drier.  Eight to 15 inches of snow were reported from Oglala Lakota County eastward to Tripp County on January 24-25 while the Black Hills received only three to eight inches. Another storm left four to eight inches of snow, with localized amounts near 12 inches, over parts of northeastern Wyoming, the eastern slopes of the Black Hills and across far southern South Dakota on February 23-24.  The final winter storm on April 9-10 produced four to eight inches of snow over northern Campbell County, the Bear Lodge Mountains, and the Black Hills while a small swath of four to twelve inches of snow fell across parts of Jackson, Mellette, and northern Tripp Counties.

Precipitation amounts varied across the region during the rest of the winter into early spring with only a small area of abnormally dry conditions noted over northeastern Wyoming by the beginning of May.  However, just over 50% of average precipitation during May—normally the wettest month of the year—led to a rapid intensification of drought conditions.  Much below normal rainfall continued through the summer.  By early July, the entire area was at least abnormally dry with severe drought covering much of northwestern South Dakota and areas of extreme drought persisting east of the Black Hills through the rest of the year.

The dry conditions also contributed to a rather mild severe weather season.  The Rapid City NWS office issued only 183 severe thunderstorm warnings—the fewest number since 1996 (the previous lowest was 187 warnings in 2002).  Some of the significant storms during the summer included:

A band of severe thunderstorms spawned several tornadoes over eastern Wyoming and the Nebraska panhandle on June 12.  Although the storms weakened by the time they reached South Dakota, quarter sized hail and 70 mph wind gusts were reported, and a small tornado was spotted southwest of Allen but caused no damage.  The straight line winds blew over a semitrailer on Interstate 90 near Kadoka.

A wind storm with gusts to 75 mph swept across southwestern South Dakota on June 27.  The Custer County Airport station recorded a peak gust of 69 mph, which is the highest gust ever recorded at that site. The Custer YMCA building lost a section of its roof, several signs were blown over and broken, and numerous trees were blown down.

The strongest storm of the season pounded the Newell area with baseball sized hail and wind gusts over 90 mph on July 18.  Several sheds and numerous trees were toppled, building and car windows were broken, and crops destroyed.

One of the most active thunderstorm days was August 14 when severe thunderstorms tracked from the northern Black Hills over Rapid City.  Large hail damaged roofs and heavy rain caused localized street flooding on the north side of town. Later in the evening, stationary thunderstorms dropped baseball sized hail and two to four inches of rain over northern Oglala Lakota County, causing flash flooding along Porcupine Creek from Rockyford to Porcupine.  A family took shelter in a church and was stranded overnight before being rescued.

Three to five inches of rain fell during the morning of August 25 across southern Ziebach County. Runoff caused flash flooding along Ash and Rattlesnake Creeks and water ran over several county and BIA roads.

The second of only two tornadoes for the year touched down on August 26.  The brief rope tornado damaged some trees south of Oelrichs near the Nebraska border.

The 2017-18 winter season started with strong winds.  Both Rapid City Regional Airport and the downtown NWS office recorded 50 mph wind gusts on eight days between December 4 and 14.  The winds continued during the nighttime hours and contributed to the rapid spread of the Legion Lake Fire in Custer State Park on December 11-15.