Flash flood watch as Twin Cities brace for 2-4 inches of rain

Dig out your umbrellas, because Wednesday is going to be a wet one.

Forecasters are predicting 2 to 4 inches of rain around the Twin Cities metro, with multiple rounds of severe thunderstorms sweeping southern Minnesota and continuing into Wednesday evening. A flash flood watch was in effect for 10 counties, including Sherburne, Isanti, Chisago, Wright, Hennepin, Anoka and Ramsey, from 10 p.m. Tuesday until 7 a.m. Thursday, said the National Weather Service in Chanhassen.

Soil is already saturated from recent storms, and river levels are higher than normal — increasing the chances of flooding. After a surprisingly wet August, storm systems will yield another heavy rainfall.

The sheer amount of water is unusual for mid-September and more typical of midsummer, said Craig Schmidt at the weather service.

The most rain we've seen in a calendar day this year was 2.17 inches on July 23, said meteorologist Paul Douglas. "So if we were to get 3 inches in the metro it would be the wettest day of the year to date," Douglas said. "I doubt we'll see 3 inches tomorrow, but we may see a rainfall total close to 3 inches by Friday."

Meteorologists are comparing this week's rain to September 2010, when 5 to 8 inches soaked southern Minnesota and caused major flooding.

"We're hoping we don't go quite that far with this one," said Schmidt, a service hydrologist. "If you've had problems in the past, then the potential is there again."

In preparation for the deluge, workers are limiting the amount of water passing through Grays Bay Dam on Lake Minnetonka, which regulates the flow from Minnetonka to the creek.

"Minnehaha Creek reacts in a flashy fashion to rainfall, [so] the water levels rise very quickly," said Telly Mamayek, communications director of the watershed. Typically, the creek will jump by about a foot per inch of rainfall.

Metro area residents may get a brief reprieve Wednesday morning, before rain returns in the evening hours. Large hail and damaging winds are also possible.

Minneapolis and St. Paul are likely to get 2 to 4 inches, while Rochester could top 4 inches. South central Minnesota, from Faribault to Northfield, and western Wisconsin will see the heaviest rain.

Liz Sawyer • 612-673-4648