Dangerous Flash Flood Threat Continues in the Upper Midwest, Including Parts of Iowa, Minnesota, Wisconsin

Jon Erdman
Published: September 22,2016
Flash flooding and river flooding have returned to parts of the Upper Midwest, and the threat for additional heavy rain will persist through early Friday.
(MORE: Flooding Slams Midwest, Prompting Flash Flood Emergency, Stranding Vehicles)
A swath of 3 to 14 inches of rain pummeled parts of central and southern Minnesota, northern Iowa, and western and central Wisconsin Wednesday into early Thursday, triggering flooding of homes, mudslides, road washouts and rapid river rises.

Three-Day Rainfall, Flood Reports

This hilly region had already been hit with flooding rain multiple times over the past several weeks since mid-August, so any additional heavy rain would quickly run off over saturated ground.
Some notable reports of flooding reported to the National Weather Service include:

• Clark County, Wisconsin: Over 60 roads closed
• Greene, Iowa: Multiple homes flooded with sandbagging occurring; flooding reported to be near 2008 levels
• La Farge, Wisconsin: West side of town flooded
• Minneapolis/St. Paul: Flooding on northwest side of the metro; I-94 closed at U.S. 169
• Nashua, Iowa: Flooded basements
• Viroqua, Wisconsin: Four feet of water on Main Street 
• Waseca, Minnesota: A few homes evacuated; U.S. 14 closed; many roads flooded with stalled vehicles; 13.91 inches of rain.

(INTERACTIVE: Storm Reports Map)
Some rivers have been pushed into major flood stage or may do so this weekend into early next week.
Parts of northeast Iowa may see crests that are only second to the records set in the floods of June 2008. This includes the Cedar River at Charles City, Janesville, Waterloo and Cedar Rapids. Though it should be noted that in some locations like Cedar Rapids, the crests will be several feet short of the 2008 records.
(FORECAST: NWS River Stages)

Current Radar with Watches and Warnings

(MORE: View National Interactive Radar Map)

How Much More Rain?

In some ways, the setup for this resembles a classic mid-summer Midwest heavy rain event – namely, a stalled, roughly east-to-west-oriented frontal boundary being intercepted by a nose of deep moisture, supplied by a "low-level jet stream" a few thousand feet above the surface.

The meteorological setup for heavy rainfall in the Upper Midwest this week.

In this pattern, multiple clusters of thunderstorms form and stall over a given area. In this case, the clusters are stalling over an area saturated from heavy rain in recent weeks.
Flash flood watches remain in effect in southeast Minnesota, northern Iowa and southwestern Wisconsin into Friday afternoon.
Additional clusters of thunderstorms are possible into Friday morning, before the front finally lifts north as a warm front during the afternoon.
Where any thunderstorms train, or continuously redevelop over the same area, an additional 1 to 4 inches of rain is possible into Friday morning, on top of what has already fallen. Most of that rain will likely fall within a short period of time.

Forecast Rainfall Through Friday

Another round of rain looks likely to move in this weekend ahead of a cold front. If the cold front moves slower than forecast, additional heavy rain and flash flooding are possible.
(MAPS: 7-Day U.S. Rainfall Forecast)
Don't underestimate the power of flood water. Never drive through flood waters of unknown depth. The majority of flash flood depths occur in vehicles. Turn around, don't drown.
MORE: Flooding in Louisiana