Southern Wisconsin Could See Four Days Of Rain, Pockets Of 7 Inches Possible

MILWAUKEE, WI — Southern Wisconsin could see rain on and off for four straight days starting Friday, with forecasters warning that pockets of the region could pick up more than 7 inches by the time it clears out early next week.

The National Weather Service office in Milwaukee/Sullivan says a low pressure system will push into the region Friday and bring precipitation that lingers through much of the day Saturday. A secondary system may extend the rain into Sunday, and forecasters say a third system could bring yet another round of rain into Monday.

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"This could make for 4 straight days of rain and potential for higher end amounts," NWS said in its Wednesday afternoon forecast discussion, adding that the setup "could introduce potential for 3 to 5 inches of rain with pockets of over 7 inches from Friday through Monday."

Here is how the timing is expected to play out in the Milwaukee area.

Isolated showers and a slight chance of thunderstorms are possible tonight into Thursday morning, with mostly cloudy skies and highs in the upper 60s to 70. Friday itself looks quiet during the day, with highs near 69 and partly sunny skies, before showers and possible thunderstorms move in after 1 a.m. Friday night.

Rain becomes more likely Saturday, with a 100 percent chance of showers and storms and a high near 73. Chances continue at 40 to 50 percent each day from Sunday through Monday as additional rounds move through.

Deep atmospheric moisture is a key factor in how much rain falls. Forecasters say precipitable water values will run above 2 inches for much of the event, which they say could make for what the agency described as "a very efficient rainfall with some lightning intermittently."

That combination of a long duration event and high efficiency rainfall has forecasters watching for flooding. NWS said the prolonged nature of the system "does yield some concerns about flooding potential, especially in the areas with highest" moisture buildup, and that while widespread flash flooding is unlikely, the region cannot rule out "potential for significant ponding of water."

The highest totals will not necessarily fall on Milwaukee itself.

The point forecast for the Milwaukee area currently shows closer to 1.5 to 2 inches of rain through the weekend, well below the 3 to 5 inch range and the isolated 7 inch pockets forecasters say are possible somewhere in the broader region. Where exactly the heaviest band sets up remains one of the biggest open questions.

Forecasters were careful to note that major river flooding is not expected. Dry soils and lower river levels heading into the event should allow for decent water absorption, which should limit runoff even with the heavy totals.

The system will also stir up Lake Michigan. Gusty southeasterly winds are expected Saturday as the low pressure system approaches, with gale potential possible at times, before winds shift northeasterly Sunday. Gusts up to 30 knots are possible across the southern two thirds of the lake through Sunday.

Looking beyond Monday, forecasters say confidence drops significantly, though drier conditions are generally expected by midweek.