March flooding - Gibbon

A pickup moves slowly through deep water at the north end of Gibbon’s U.S. Highway 30 overpass March 14.

KEARNEY — The short-term weather outlook University of Nebraska-Lincoln Associate State Climatologist Al Dutcher gave Feb. 5 at the South Central Water Conference in Holdrege predicted a tough calving season and wet planting season.

Dutcher told the Hub Monday he had no idea then about what was to come a month later. “The thing about this business is it will make you an honest fool real quick,” Dutcher said.

He was at the Kearney Holiday Inn — which was flooded in July — to give a spring flooding presentation to members of the Nebraska State Irrigation and Nebraska Water Resources associations. He joked that it’s easier to be accurate when describing what happened than when forecasting what will happen.

The widespread March floods were linked to a “bomb cyclone,” defined as when atmospheric pressure drops 24 millibars over 24 hours. Dutcher said it doesn’t happen often, but it likely will occur again.

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More rare was the mix of other factors that turned the March 13-14 winter storm into a historic Nebraska flood event.

Deep surface and upper atmosphere lows pulled up from the Southwest as Gulf of Mexico moisture wrapped around the system’s back side all the way to Canada. “It’s why there was such a precipitation event with this storm,” Dutcher said.

The lineup of other factors started with saturated soils from a wet 2018 growing season and fall.

Then came two distinct seasons in February: dry and warm the first two weeks and frigid and snowy the last two weeks.

As an example, he said that in the second half of February, the city of Valentine’s temperatures averaged 19 degrees below normal and there were eight consecutive days of snow.

More snow came at the start of March, along with high winds that moved much of it into ditches, Dutcher said.

The saturated ground froze, but there also was some melting below the frozen surface of the snow. He said that liquid froze again, creating a perfect layer to “easily slide water and have runoff” that had nowhere to go.

With temperatures averaging 24 degrees below average the first seven days of March, Dutcher said soils froze to 24 inches deep and ice grew to 18-24 inches thick in lakes and rivers. Ice broke loose during the bomb cyclone.

During the storm’s 18-24 hours, almost 1½ inches of moisture fell as rain and several inches of snow, he said, describing the conditions as a “cascading effect in areas with the greatest snowfalls and coldest temperatures.”

Dutcher said Nebraskans often see localized flooding in the spring, but now know that a repeat of conditions seen last February and March could be a sign to watch for bigger, more widespread floods.

The 2019 flood was the second or third such event in the Upper Midwest during the past decade, Dutcher said, including the 2011 flood in the Upper Missouri River Basin. However, the last similar flooding in Nebraska was in the mid-1960s.

“Expect the unexpected and don’t expect it every year,” Dutcher said about the weather. “... Don’t ask me when we’ll see it again. I can’t answer that.”

One reason, he added, is that the effects of climate change are not known.

“I hope we don’t have to have this discussion again in four or five years, or 20,” Dutcher said.“In my business, there’s no such thing as a normal year.”

One factor already on Dutcher’s spring 2020 flooding watch list is saturated soils. He told the Hub that because of wet conditions throughout the summer, soils are more saturated now and in a larger area of Nebraska than a year ago.

“But again, you still need to have the triggers” to produce flooding like what was seen in March, Dutcher said. “ ... What we don’t want is another big snowmelt in 24 hours or frozen streams with 1½ feet of ice that has to release at some time.”

He added that runoff choke points are among the factors to address before the next big flood, including culverts going into field and under highways in rural areas that couldn’t handle the high 2019 water volumes.

Dutcher said “The Perfect Storm” movie title is an appropriate description of what happened in March. Weather data and new technologies gave meteorologists the tools to watch the historic storm’s many parts come together over several weeks.

“To see it before your eyes, that’s the difference between this one and 40 years ago,” he said.

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