– In the teeth of a harsh northwest wind lashing across the barren white expanse otherwise known as Lake Pepin, Al VanGuilder and Bill Chelmowski are looking for spring.

Technically, this U.S. Army Corps of Engineers crew is taking its first measurements in its annual ice survey of this key stretch of the Mississippi River, trying to get an inkling for when the first towboat might break through to St. Paul to open the navigation season. So, yes, undeniably, by extension they are also looking for a glimmer of spring.

Forget the groundhog’s shadow; this is science.

“The first towboat to reach St. Paul is kind of a big deal,” said Patrick Moes, spokesman for the Corps. “It’s the first sign of spring. Especially this year, we could really use it.”

The survey is part of the Corps’ task of maintaining and monitoring the river’s navigation system, which is vital to the Upper Midwest’s economy. The weekly results are tracked by river shippers eager to get to work for the new season.

Nearly 5.5 million tons of commodities passed through Twin Cities river terminals in 2012, much of which was grain — 60 percent of the nation’s exported grains are shipped on the Mississippi. From southerly river ports, commodities like gravel, fertilizer, salt, cement, and coal also make their way to Minnesota.

Usually, the survey crew is out on the lake by mid-February — in 2013, the first measurement was taken on Feb. 13, exactly two weeks earlier than this year. To those anxious to ditch winter’s bitter chill, that might be the first discouraging clue about what this year’s ice foretells.

“We’re expecting to see a lot of ice thicknesses at levels that we’ve never seen before,” said VanGuilder, a supervising civil engineering technician who has been measuring the ice for the past 16 springs.

The ice measurements, taken at 17 points on the 21-mile-long lake, are typically done once a week until the first towboat punches through.

But with so much ice on Pepin now and more cold weather in the forecast, VanGuilder said, “we’ll probably skip next week’s measurement, just because we’re going to find such thick ice out here today. It’s not going to be worth our while to go out, because we’re not going to be seeing significantly warmer temperatures by then.”

Last obstacle

Lake Pepin, which starts south of Red Wing and extends to Reads Landing near Wabasha, is the last hurdle for the start of the river shipping season. The largest lake on the entire Mississippi, its size and depth — to more than 40 feet in places — slows the current and leads annually to a massive freeze-up.

Dan Cottrell, regional channel maintenance coordinator with the Corps, said 28 inches of ice is the thickest measured at Lake Pepin since the survey began. But he said this year he wouldn’t be surprised if it reached 36 inches in spots. The numbers should appear on the Corps’ website: www.tinyurl.com/ajy6fnt.

The 10-year average for the first towboat arrival in St. Paul is March 24, Cottrell said. Last year’s late spring pushed the date to April 9. But every year is a guess — there’s no predicting now how warm weather, rain and other factors will affect that pivotal date.

“This is in the hands of Mother Nature, and, as much as we might not like it, Mother Nature always wins in this deal,” said Lee Nelson, president of Upper River Services Inc. in St. Paul, which moves barges between river terminals.

Working in the cold

Out on the lake, VanGuilder revs up the 385-horsepower engine of the light airboat, the kind often seen in the Everglades. It bounces off the boat ramp and then skims atop the snow-crusted ice, bouncing off small drifts and brilliant in the morning’s crisp sunshine. The huge propeller drones like a small airplane, kicking up a huge wash of snow in its wake.

For safety, VanGuilder and Chelmowski are outfitted in heavy crash helmets and flotation jackets. At one spot, they stop, and Chelmowski pulls out the long ice auger that, whining like a chain saw, chews a small circle in the ice until a small fountain of river water burbles through. VanGuilder measures it with a marked steel rod.

The measuring points are located along the lake’s “sail line,” the route navigated by the towboats.

The men are looking for two types of ice. Blue, or black ice, is compressed and solid and harder to break through. White ice results from thawing and freezing cycles and as a result, holds air bubbles that make it softer.

“This is all blue ice,” VanGuilder said. “We won’t be seeing any white ice until later.”

The Corps does not have an ice-breaking ship for the Mississippi — being heavy craft, it would be difficult to navigate the ship through the 9-foot-deep channel used by the towboats.

Typically, shippers like to see ice less than 20 inches thick before trying to break through to St. Paul, though the first towboat last year smashed through a barrier 22 inches thick. The ice is broken by using an empty barge followed by a string of loaded barges to give it the extra oomph to plow through.

On this bitterly cold February morning, as VanGuilder pulls the measuring rod from the hole, a seasonal ritual he will repeat many times in coming weeks, he is asked half-jokingly if he can detect any sign of spring from beneath the ice shelf.

“Definitely not,” he replied, wryly.