Issued by NWS North Central River Forecast Center
AGUS73 KMSR 241739
Hydrometeorological Forecast Discussion
NWS North Central River Forecast Center Twin Cities/Chanhassen MN
1240 PM CDT Wed Aug 24 2016
In the last 24 hours, a MCS thunderstorm complex developed in
northwest Iowa yesterday afternoon. This storm intensified with
multiple rounds of storms as it tracked along the Minnesota-Iowa
border and over northeast Iowa into Wisconsin overnight. Less
intense storms moved across most of the rest of Iowa, northwest
Illinois, Missouri and parts of North Dakota and northern
Minnesota. The heaviest rain fell in a broad line from the Iowa
Counties of Howard and Chickasaw, across Winneshiek, and Allamakee
counties into Crawford and Richland counties in Wisconsin. There,
five to six inch rainfall totals were common with 8.46 inches
observed in Decorah Iowa. Quarter to one and a half inch totals
were scattered across neighboring parts of Iowa, Minnesota,
Wisconsin and Illinois. The North Dakota showers dropped only a
tenth or two.
This morning, the MCS has re-oriented into a faster moving line of
thunderstorms and is now moving through Illinois and Wisconsin
into Michigan. Light showers are trailing behind the line,
including parts of Iowa near last night`s epicenter. As the day
moves on, afternoon development is expected on the south end of
the boundary in northern Missouri and is expected to expand
overnight into central Illinois. Widespread totals are expected
to be in the one to two inch range in this area, but higher
amounts are likely depending on location and movement of storms.
Tomorrow, the surface boundary begins to fall apart, as surface
high pressure moves in. Upper level atmosphere support still
exists into the weekend though, so less organized thunderstorms
are still likely each day... especially in the southern two-thirds
of the NCRFC area. Rainfall totals should be lower in the one to
two inch range, topping out around three inches. Placement of the
forecast is more difficult and dependent on differential daytime
heating of the surface.
The heavy rain described above over northeastern Iowa is causing
major flooding in the Turkey and Upper Iowa River Basins.
The forecast precipitation for the next 24 hours is not expected
to cause additional flooding. However, there is significant
uncertainty in the amount and location of the forecast
precipitation. It is possible that we could see rainfall amounts
similar to those reported in northeastern Iowa this morning.
For additional and more in-depth information concerning river
forecasts, precipitation and all hydrometeorological information
in the NCRFC area of responsibility, please refer to the NCRFC
web page at: http://www.weather.gov/ncrfc
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