SIOUX FALLS, S.D. (KELO) — It was a lot like a hurricane whipping through the state.
The May 12 storm that covered roughly 300 miles in eastern South Dakota and killed two people brought winds of hurricane speed, said KELOLAND meteorologist Brian Karstens. Wind speeds of 75 mph or higher were reported and those are hurricane speed.
“Yesterday the sheer volume of reports the second highest total in the United States since 2004, for those hurricane force like winds in one single system. When you look at the plains of South Dakota it was a very historic day,” Karstens said.
Karstens said there were 169 reports of wind with about 60 of those reports of winds of 75 mph or higher.
The highest gust was 107 mph in Tripp.
The highest wind speed reported to the National Weather Service’s Aberdeen office so far was 102 mph at the state recreation area on Lake Cochrane, at the Minnesota border, Travis Tarver, a meteorologist with the NWS in Aberdeen said.
“The majority of our higher end was 80 mph to 90 mph,” Tarver said. “That was fairly widespread.”
The possible high winds that became reality were part of how the NOAA/NWS Storm Prediction Center categorized the risk from the storm.
Severe thunderstorm warnings can mainly be for small hail, Karstens said.
“But the categorization yesterday was a Particularly Dangerous Situation (PDS),” Karstens said. It was the first PDS of his 22-year career at KELOLAND, he said.
A PDS declaration from a storm could cross a threshold of severity, Karstens said. The severity could include 80, 90 to 100 mph winds.
“That watch that came out from the Storm Prediction Center yesterday at 3 p.m. signaled that,” Karstens said of a PDS. The potential for high winds and the potential damage was emphasized with KELOLAND weather reports throughout the late afternoon.
“This easily beats anything I’ve ever seen in South Dakota,” Karstens said
The storm risk was also declared as moderate, which means “we are getting to the higher end of risk,” said Travis Tarver, a meteorologist with the National Weather Service in Aberdeen. The categories are slight, enhanced, moderate and high, Tarver said.
“High risk, you usually see those in the southern part of the country with tornado outbreaks” Tarver said.
Three NWS survey crews were out on May 13 to evaluate storm damage and determine if it was caused by straight line winds or tornadoes, Tarver said.
The NWS did issue several tornado warnings on May 12.
A tornado was reported on May 12 in Castlewood which damaged multiple buildings including the school.
While the storm produced some reported tornadoes, it also showed that high winds can cause severe damage across a wide area, Karstens said.
The NWS in Sioux Falls covers 45 counties in a four-state area. Meteorologist Todd Heitkamp said only one county, Brule County, South Dakota, has not reported storm damage.
Perfect mix for a big path storm
“As far as the storm itself, it was a somewhat rare event,” Tarver said.
“Looking at the geography on this whole thing it started in portions of central Nebraska, it really intensified up to O’Neil southwest of Yankton,” Karstens said. “When it crossed the Missouri river into South Dakota, it continued to develop all way up to southeastern North Dakota and a big portion of Minnesota received wind as well,” Karstens said.
But why did it start and cut such a wide path of sustained wind?
“The atmosphere was angry,” Karstens said.
“The atmosphere was so primed and ready to go, it’s the things you see in textbooks that you teach about,” Tarver said.
An angry atmosphere was set up by wet conditions in North Dakota and drier conditions to the south, Karstens said.
Add in hot temperatures and humidity such as 94 degrees in Sioux Falls and southern winds.
Humidity was more like July or mid June, Karstens said.
The May 12 conditions were ripe for a storm but the tone was set months before when tornadoes happened in Iowa and storms happened in April in South Dakota, he said.
“We’re coming off the windiest April on record,” Karstens said.
The jet stream to the south is moving northward already as Texas as been heating up to 100 degree already this spring. North Dakota and even northeast South Dakota are wet.
And an Artic front is in a blocking pattern which helps to set up collision zone for weather, Karstens said.
“As long as North Dakota is wet we are in a clash zone,” Karstens said.
The clash or collision helped to cause the storm’s winds and lifespan, he said.
The warm front across the state helps storms sustain themselves, Tarver said. The May 12 storm also created its own cold pods which helped to keep it moving across the state.
There were pockets of tornadoes within the storm
“The atmosphere was behaving in such a way that the wind sheer at lower level altitudes was changing directions,” Tarver said.
That can create spin ups and brief circulation which can produce tornadoes, Tarver said.
“There was a lot going on yesterday,” Tarver said.
As to if it can happen again this spring or summer, Karstens said much depends on how wet is stays in northeastern South Dakota and North Dakota and how dry it stays to the south.
The weather pattern is in a LaNina which caused a tendency for more tornadoes in the south in 2008 and 2011, he said.
La Nina is a weather pattern of unusually cold ocean temperatures in the Equatorial Pacific, according to NOAA. It influences the hurricane season, has links to springtime tornado activity, and can increase the chance of drought in some regions.