Heavy April showers turning Minnesota puddles into ponds

Even with May around the corner, Mother Nature is proving to be unrelenting.

Heavy rain and chilly temps turned puddles into small lakes, sump pumps were working overtime and no one seemed sure whether to wear a rain coat or a parka. Waterlogged ground, combined with wind gusts pushing 40 miles per hour, likely caused a tree to topple onto a house in St. Paul and a massive retaining wall in Minneapolis to come tumbling down. Up North, freezing rain brought down power lines.

And no letup appears to be in sight. Heavy rains and strong winds are forecast through Friday, with a chance of snow Tuesday night and into Wednesday.

In Minneapolis, flooding closed Wirth Parkway from Golden Valley Road to Plymouth Avenue. It could remain closed until Thursday if rains continue as forecast.

Monday's rain alone, .67 inch by 4 p.m., pushed this April from the ninth-wettest to fourth-wettest on record. Total rainfall for the month through late Monday afternoon was 5.61 inches, almost exactly 3 inches more than the April average and closing in on the record of 7 inches.

"It would be a trick to do it," said assistant state climatologist Pete Boulay, noting there are only two days left in the month. "I'd need another juicy event."

When was the last time it rained so much in April? That would have been last year. The 5.22 inches of rain in April 2013 had been fifth most on the books until Monday, when it fell to sixth.

No serious risks of river flooding were posted by the National Weather Service as of Monday.

Uprooted trees are often a problem during aggressive storms, said Brad Meyer with the forestry division of St. Paul's Parks and Recreation Department.

"It's not unprecedented by any means," he said of the fallen trees, a result of what foresters call windthrow. Already the department has removed five trees over the past couple of days, and Meyer said he expects to remove a few more by week's end.

A combination of tree health and wind and rain working in tandem significantly weakens a tree's resistance. While healthy trees have a little flexibility to them, a diseased tree may be more rigid or have weaker trunks and branches that are eaten away by decay, said Craig Schmidt, a hydrologist with the National Weather Service.

But healthy trees with especially full foliage may also be at heightened risk because the net of flexible branches and leaves act as a sail that better catches the wind, Schmidt said.

Waterlogged soil also plays a role in uprooting trees, Schmidt said. Soggy ground means that roots loosen up and become almost suspended as moisture makes its way farther into the earth. This weakens a tree's anchor to the ground and diminishes its ability to stand up to wind, he said.

"A lot of trees out there look perfectly healthy," St. Paul's Meyer agreed. But because of soggy soil these trees "will come down without rhyme or reason."

Apart from trimming and keeping tabs on the health of the trees in your yard, there isn't much you can do to prevent storm damage to trees, Schmidt said.

Meyer said to look out for new movement in trees, such as leaning or exposed roots that haven't always been there. "That's the easiest sign to tell if it's a hazardous tree," he said. Being watchful of newly planted trees that have yet to take root is also a good idea, he said.

Staff writer Bill McAuliffe contributed to this report.