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John Myers, Forum Communications Co., Published June 20 2012

Rain likely largest storm in Duluth history

DULUTH, Minn. – This week’s rainstorm might well be the largest in Duluth’s recorded history, dating back to the 1870s, said Dan Miller, science and operations manager for the National Weather Service in Duluth.

Tuesday’s 4.2 inches was second only to 5.2 inches on July 21, 1909, for a single calendar-day rainfall. But the two-day rain total of 7.25 inches in Duluth – and nearly 10 inches in Two Harbors – may indeed be a local record for a single storm.

“This is right at the top for rainfall and flooding events in the history of the city of Duluth, no question,” Miller said. “We’re looking to see how it compares. But in terms of infrastructure damage and impact on people, this is right there with 1972, if not more – at least from what we know of it.”

Although moisture levels are typically much drier during the winter, Weather Service meteorologist Dean Melde said an inch of rain usually equates to between 10 and 12 inches of snow. So the current system could have dropped 60 and 70 to 80 inches of snow on Duluth.

The water that fell simply had no place to go, Miller noted, as the ground was already saturated, and local streams and ponds were already full after soaking rains Saturday and Sunday.

The Tuesday-Wednesday freak rainstorm came in waves of downpours, some nearly 2 inches per hour, interspersed with lighter rain, from about 5 p.m. Tuesday into Wednesday afternoon.

The lingering downpour was spurred by an unusually large amount of moisture in the atmosphere that coupled with a slow-moving, virtually stalled front, said Dean Melde, meteorologist for the Weather Service in Duluth.

Meteorologists had forecast heavy rain potential for days, but they didn’t realize how heavy until about the time the rain started, Miller said.

Greg Spoden, Minnesota state climatologist, said this was the region’s “1 percent storm” or what old-timers used to call the 100-year flood.

“We really don’t have enough years of data to compare these to, but this was a storm you would have about a 1 percent chance of seeing on any given year. And you got it across a pretty wide area up there,” Spoden said.

The rainstorm also ranks among the larger in state history, Spoden said, but falls far short of the 16 inches received in 24 hours in August 2002 in Hokah in far southeastern Minnesota, which caused massive flash-flooding and millions of dollars of damage.

The infamous storm of August 20, 1972, dropped up to 4 inches on parts of Duluth in less than two hours, causing massive flash-flooding and damage in the city’s Hillside. Much the same as this week’s event, the 1972 storm came after the city already was saturated from ample rainfall in the weeks leading up to the storm.

According to storm documents from the University of Minnesota, the 1972 storm caused an estimated $12 million in damage and was called Duluth’s worst natural disaster to that point. To put that in perspective, that’s about $66 million in 2012 dollars.

In 1972, another heavy rain fell on Duluth on Sept. 20, up to 5.5 inches, just a month after the August flood, causing an estimated $1 million additional damage.

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John Myers writes for The Duluth News Tribune