Southern Minnesota on alert as heavy rain forecast raises risk of flash floods

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Parts of southern Minnesota are at risk from possible flash flooding as the state prepares for a massive deluge of rain Thursday into Friday.

Meteorologist Paul Huttner wrote on MPR News' Updraft blog that remnants of Hurricane Blanca are heading to the Midwest, bringing potential "damaging and life-threatening" flash floods to southern Minnesota and northern Iowa.

The National Weather Service (NWS) issued a weather alert Wednesday afternoon, saying potential for flash flooding is "moderate to high" south of the metro area, as "fast rising streams, drainages and low spots should see some flooding Thursday into Thursday night."

Two to 4 inches of rain is expected to fall from Thursday afternoon through Friday morning, but as much as 6 inches could fall in local areas, according to the NWS office in La Crosse, Wisconsin.

"With some rivers already somewhat elevated from recent rainfall, there is a heightened concerns for bank full rises, and possibly minor to major flooding on some streams and rivers across the area," the weather service says.

An advisory issued by the Minnesota Department of Transportation warns motorists that "roads may be closed or restricted without warning as flash flooding is difficult to predict. "

MnDOT urges those who must drive during a storm to check their 511.org website for up-to-date road closing information.

But where the heaviest rain will fall is still uncertain, with the NWS Twin Cities saying one model predicts southern Minnesota will bear the brunt on Friday – with up to 3 inches falling on ground already saturated from Thursday night – but another model suggests the worst will fall in Iowa.

"The exact location of the heaviest rainfall remains in question. The latest information would place the heaviest rainfall axis from southeast Minnesota into north central Wisconsin," the weather service notes.

If the rainfall is at the maximum level being forecasted currently, it could lead to flooding on rivers flowing into the Minnesota and Mississippi in the southeast of the state and in Wisconsin, as well as the Minnesota River downstream from New Ulm.

The Pioneer Press reports the Twin Cities is set to get its biggest soaking of the year, with 2.4 inches of rain expected on Thursday and Friday.

This would comfortably beat the 0.79 inches that fell on May 10 and 11, the biggest rainfall in the metro area in 2015, and would be most rain seen in the Twin Cities since June 19 last year, when 4.13 inches fell, the Pioneer Press says.

It will mean a week of extremes for Minnesota, after temperatures in many parts of the state broke the 90-degree barrier on Tuesday.

According to Accuweather, temperatures in the Twin Cities on Thursday and Friday are likely to be cooler, in the 60s, before rising to the mid to upper 70s on what should be a sunnier weekend.

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