Digging deep to predict spring floods

A wide-ranging sampling of the snowpack around the region started Monday morning, which will provide the National Weather Service and other weather observers with key information as they determine whether record snowfalls around the region will turn into spring floods.

If there's going to be flooding in Minnesota or the surrounding states this spring, the first indication may come from a loop on the snowmobile trail at the edge of the Lamprey Pass Wildlife Management Area in Anoka County. Technicians from the Army Corps of Engineers started their work there, checking to see how much water is in the snow.

Hydrological technician Bill Odell pushed a 3-foot metal tube into the snow, pulled it out and dumped the contents into a gallon plastic bag, banging on the side to get all the snow out.

"Each location we go to, we'll collect five samples and we'll average that out over the specific location," he explained. "Over the next week and a half to two weeks, we'll be traveling about 4,000 miles to about 110 different locations. Each of those locations will give a representation for that general geographic area."

Odell takes the bag and weighs it on a scale in the back of his truck. He records each stop on a page in a three-ring binder. In Columbus, Minn., it's about 20.4 inches of snow with about 4 ounces of water — the equivalent of 4 inches of water standing on the ground if it all melted at once.

By itself, that doesn't tell you much. But over time, the Corps has been gathering minute detail of what happens in winter and what happens the following spring.

"Each year we come back to the same location, so we can kind of get that same feel for what the conditions are year to year for that area and that region," Odell said.

And while the amount varies widely from place to place, climatologists say they're seeing one thing right now: lots of snow.

The most recent flood forecast issued Thursday showed most of the state had between 18 and 36 inches of snow on the ground, according to Pete Boulay, climatologist with the Minnesota Department of Natural Resources.

"And if you take that snapshot for Feb. 28, compare it to all the previous end of Februaries ... a lot of places are in the near deepest snow for that date," Boulay said.

That includes some of the big flood years — like 1965, which had what the National Weather Service called the "flood of record" for the Mississippi for most of Minnesota. That year, there was about 13 inches of snow on the ground at the end of February — although Boulay said it was the 37 inches in March that really made the difference.

Other factors come into play as well, like whether it gets cold enough at night to pause snowmelt, or the snow melts continuously and more quickly.

But Patrick Loch, spokesperson for the Corps, said a lot of eyes will be on the data that Bill Odell collects as far north as the Canadian border through mid-March. The U.S. Geological Survey monitors the information, as do the Corps planners that summon bulldozers and dump trucks to fight big floods.

"We're going to use this data for the National Weather Service for their forecasting, and our interest is because we'd be part of that emergency response," he said. "But also, our operations division, we're going to want that information as we continue to operate these structures, whether the flows are high or low."

There are all kinds of other numbers that go into flood forecasting, like the thickness of winter ice, how much rain fell last fall, and how far down the soil is frozen. All told, they point to a likelihood of flooding that's already well above normal. But what happens in the next four to six weeks will probably make all the difference.