It’s official: The Yankton area is seeing one of its soggiest summers ever.
In the last two months, Yankton has received 16.90 inches of rain according to the National Weather Service, which is a record for the two months. The yearly average as of Aug. 2 is 15.40 inches.
Yankton isn't the only place that has received record rainfall this summer. Vermillion has received 19.25 inches of rain, also a record, during the last two months.
Wakefield, Neb., which is 70 miles southeast of Yankton, had its wettest two months of the summer in history with a total of 16.95 inches.
Tyndall recorded its second wettest June and July with 15.61 inches of rain, and Menno has received 14.27 inches.
The wet summer is an anomaly as well. According to the NWS, Yankton hasn't had a summer with this much rain since 1993. The only other summer that was wetter was in 1908.
“This is very abnormal; the rain usually doesn't pile up like it has in the last two months,” said Kyle Weisser of the NWS.
For the year, Yankton has unofficially received 28.26 inches of rain, almost double the current yearly average.
Weisser said some areas in South Dakota have gotten its yearly average in the last two months.
“Yankton, Sioux Falls and Sioux City's average is 22 to 27 inches, so a lot of sites are already over their yearly average,” he said. “I know a couple parts of Sioux Falls had 22 inches since June 1, meaning that they have had their highest annual rainfall in the last 60 days.”
The last seven months have reversed the drought of the last two years. In 2009, Yankton had a total precipitation of 21.03 inches, and in 2008 the total was 17.83 inches.
Weisser added that the NWS knows why it's raining more than usual.
“There is a pattern that has been drawn up with westerly winds that have been created by the way the jet stream runs right now, which had given us a better chance at low pressure systems like we have received,” he said.
However, Weisser said there is no explanation of why the jet stream has set up the way it has.
“It's just the luck of the draw,” he said. “Sometimes there are different oscillations such as El Nino or La Nina, and new research is being worked on for predicting wet summers and when they will happen. But right now, there is no answer to how they lock in the way they do.”
The record for yearly precipitation in Yankton is 38.2 inches, which was set in 1944, so the city has five more months to surpass that record.
But Yankton would still have to receive above average precipitation to surpass that mark since the normal amount for the last five months is eight inches.
“In August, September and October, we can still get some good events, but there is a way to go yet,” Weisser said. “We would still have to be above normal to break the record.”