Minnesota: from drought to flood potential in a month

The days of talking about the expanding drought are over, at least for the time being, as more rain moves into parts of the state. Minnesota has gone from a widespread moderate to severe drought in early May, to potential flooding in early June.

 

 

All it took was a few good rain events and the state is now considered to be drought free. While a little rain could still be used in parts of the north, many areas are now pretty saturated and could use a week or two of dry conditions. But this is fairly normal for Minnesota. June is our wettest month averaging more than 4 inches of rain statewide. The majority of our heavy rain and flooding events actually occur in the month of June with rains typically trailing off slowly the rest of the summer. 2014 was a perfect example with near record rain and flooding in May & June, but by August, much of the area was parched from several weeks of warm temperatures and sunshine.

So how do we know when flash flooding can occur? The National Weather Service uses soil moisture reported conditions from the Regional Climate Centers across the country as well as recent rainfall to assess potential flash flood amounts over each county in the US. It is then thrown onto a map that looks like this…

 

This is a map that shows the amount of rainfall it would take over a 3 hour period to produce flash flooding over the area. You can see the counties that are wetter or dryer than others OR have more pavement. For example, the heart of the Twin Cities metro would take slightly less rain than areas around it because of all of the paved areas. Much of southern Minnesota would need 2-3" of rain over the course of 3 hours to hit this criteria. Because of the anticipated widespread heavier rains expected Thursday, the National Weather Service issued the Flash Flood Watch showing that conditions are favorable for flash flooding.

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