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John Myers, Forum News Service, Published June 15 2013

Duluth Flood, 1 year later: Weeks of rain set the stage for historic deluge

DULUTH, Minn. – Downpour. Break. More downpour. Streams overflow. Flash flood. Massive damage.

It’s easy to explain what happened on June 19 and 20 of last year. It’s a little more complicated to explain why.

The seeds to the June flooding actually were sewn in May when a wide swath of central and eastern Minnesota received near-record monthly precipitation, according to the Minnesota Climatologist’s Office.

At 6.61 inches, it was the sixth-wettest May in Duluth’s recorded history. Some parts of the city saw flooding, such as wet basements and water filling low spots on roads, when nearly 3 inches of rain fell May 23 and 24.

That typically would have been the biggest rain of a normal summer. And it was important, because all that May rain filled up wetlands, bogs, lakes and streams and completely saturated the ground.

But it was just a warm-up for what was to come.

Many areas received another 2 to 4 inches of rain over the first two weeks of June, again filling every natural body of water to the brim. Duluth, many people probably don’t recall, received a quarter-inch of rain June 10, nearly an inch June 13-14 and about the same amount June 16-17, two days before the big event.The natural system of moving water – or at least what remains of the natural system after development, dams, bridges and blacktop covered the landscape – was simply unable to handle any more.

Of course, much more water came when the June 19-20 deluge hit, an all-time record rainfall that in some areas exceeded the so-called 500-year flood event. According to the National Weather Service Hydrometeorological Design Studies Center, some areas of Duluth likely topped the 1-in-1,000-year rainfall for a 24-hour period.

“The ground never had a chance to recover. The hydrological system never had a chance to dry out,” said Dan Miller, science and operations manager for the National Weather Service office in Duluth.

Officially, the weather service at Duluth International Airport recorded 7.25 inches of rain over those two June days. But many nearby rain gauges showed 8, 9 and even 10.1 inches.

Stalled front, massive amounts of moisture

The meteorological explanation of what happened is rather simple. But the recipe may not come together the same way, in the same place, for another 500 years.

On Tuesday, June 19, a cold front that had moved south across the area the previous day began to return north as a warm front. That set up a stationary front just south of Duluth. This helped provide continuous “lift” or energy for thunderstorms that developed over east-central Minnesota tracking northeast into the Duluth area, the North Shore and into northwestern Wisconsin.

The official rainfall in Duluth on the June 19 was 4.14 inches. The thunderstorms finally ended June 20 when a strong cold front moved through during the afternoon, but not before dumping another 3.11 inches at the airport.

During the deluge, warm air and moisture continued to pour into the region from the south. It welled up over the Midwest, Miller noted, funneling directly into northeastern Minnesota and into the stalled front like smoke through a chimney that narrows at the top.

On Monday, June 18, the weather service issued a flash flood watch for much of northeastern Minnesota. By 7 the next night, the Duluth weather service updated to a warning that put it bluntly: “A high-end and life-threatening flash flood event appears to be developing across a large part of northern Minnesota.”

Usually, thunderstorms develop, move over an area and then go away as the front moves by. But on those two days, the front stalled, the thunderstorms kept developing over Aitkin and Carlton counties, and they kept moving over the Duluth-Superior, Wis., area.

“You could sit and watch (on radar) the cells develop one right after the other. They just kept hammering the same areas over and over,” Miller said.