2023 Spring Flood Outlook - Updated March 23, 2023

Spring Flood Outlook Update  

Key Points

• Well above normal spring flood risk for the Mississippi River.  
   
• Near normal spring flood risk for local tributary rivers. 

• The flood risk has decreased slightly during the past 2 weeks due to drier than expected conditions in the local area. 

• This will be the last Flood Outlook issued, however the NWS Quad Cities will continue to provide regular updates throughout the lead up to and during the Spring Flood Season. 

Details 

The spring flood risk is well above normal for the Mississippi River, and near normal but increasing for local tributary rivers across the NWS Quad Cities Hydrologic Service Area. The flood risk has increased during the past 2 weeks due to additional snowfall in the upper portion of the Mississippi basin. For local tributaries the risk is also increasing due to moistening soils and higher current streamflows.

Snow water equivalent is much higher than average in the upper portion of the Mississippi basin and has continued to grow since the first outlook. Additional precipitation events and the rate of snowmelt in the upper Mississippi basin will be the main factors determining the severity of the flooding this spring.

Some factors contributing to the current risk levels include: 1) Lack of deep and widespread snowpack in the local area, while the upper reaches of the Mississippi River basin has above average snowpack. 2) A general lack of deep, hard frozen ground across the upper Mississippi River Basin. 3) Above average winter precipitation levels and above normal river levels.

.Key Takeaways…

* Even though the overall risk of spring flooding is well above average on the Mississippi River, this does not guarantee that high impact flooding will occur. The severity of any flooding will be determined by the key factors mentioned above. In particular, we will be monitoring the temperature and snowmelt trends in the Mississippi River headwaters and whether there are any large rain on snow events.

* Snow cover and snow water equivalent were well below normal across much of the local area, which decreased the overall flood threat. However, the snow water equivalent in the headwaters of the upper Mississippi River basin are well above normal and increased again from the previous outlook. A rapid snowmelt occurring over still frozen ground would increase the likelihood of high impact flooding on the Mississippi River this spring. A slow, steady melt would decrease that threat. 

 * Widespread above normal soil moisture levels in the local area reduces the capacity of the soils to soak in spring precipitation and does less to mitigate the near term flood risk as well as slightly increase the risk for prolonged flooding. We will continue to monitor soil moisture conditions as they have continued to moisten over the past months.

 * Lower than expected precipitation over the past 2 weeks have caused stream flows in the upper Mississippi watershed to currently be running near normal, meaning there is some added capacity to handle heavy spring rains than there was 2 weeks ago.

Many factors are considered when determining the overall flood risk for the upcoming spring season.  The combination of these influences factor into the final determination. These factors are discussed in detail in the next few tabs and also in the Statistical Hydrological Outlook linked below.

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Use the links below to find the Graphical Probabilities and the Numerical Probabilities, respectively.
 

Graphical Hydrologic Outlooks	Spring Flood Risk One-Pager (PDF)   (Mar 23, 2023)	Statistical Hydrologic Outlook   (Mar 23, 2023)
Images below are examples which link to the Wapsipinicon River near DeWitt. Find all other locations in the Quad Cities Hydrologic Service Area in the drop down menu below.       Select Location: Mississippi River at Dubuque L&D 11Mississippi River at DubuqueMississippi River at Bellvue L&D 12Mississippi River at Fulton L&D 13Mississippi River at CamancheMississippi River at Le Claire L&D 14Mississippi River at Rock Island L&D 15Mississippi River at Illinois City L&D 16Mississippi River at MuscatineMississippi River at New Boston L&D 17Mississippi River at KeithsburgMississippi River at Gladstone L&D 18Mississippi River at BurlingtonMississippi River at Keokuk L&D 19Mississippi River at Gregory LandingMaquoketa River at ManchesterMaquoketa River at MaquoketaWapsipinicon River at IndependenceWapsipinicon River at AnamosaWapsipinicon River at De WittCedar River at VintonCedar River at Cedar RapidsCedar River at ConesvilleIowa River at MarengoIowa River at Iowa CityIowa River at Lone TreeIowa River at Columbus JunctionIowa River at WapelloIowa River at OakvilleEnglish River at KalonaSkunk River at SigourneySkunk River at AugustaDes Moines River at KeosauquaDes Moines River at St FrancisvilleFox River at WaylandPecatonica River at FreeportRock River at ComoRock River at JoslinRock River at MolineGreen River at GeneseoLa Moine River at Colmar   Go

Current/Forecast River Conditions

Current Conditions	Forecast Conditions	Long-Range Outlooks

Link To Advanced Hydrologic Prediction Service (AHPS) and Additional River Forecast Resources

Flood Category Definitions

• Minor Flooding - minimal or no property damage, but possibly some public threat or inconvenience.
• Moderate Flooding - some inundation of structures and roads near streams. Some evacuations of people and/or transfer of property to higher elevations may be necessary.
• Major Flooding - extensive inundation of structures and both primary and secondary roads. Usually significant evacuations of people and/or transfer of property to higher elevations.  

What Are The Risk Factors For Flooding? 

Many factors are have been considered when determining the overall flood risk for the Spring, with the combination of these influences factoring into the final determination. These factors are discussed in detail below.

Seasonal Precipitation

Precipitation from the winter into early Spring continues to average near to well above normal for all of the NWS Quad Cities Hydrologic Service Area (HSA), as well as locations to the north. Analysis from the Midwest Regional Climate Center (MRCC) shows locations mainly north of Hwy 30 in eastern Iowa and northwest Illinois around 100-175% of normal during the period. Further north, these values increase to around 200-300% of normal, especially from south central Minnesota into northwest Wisconsin. The well above normal precipitation is leading to increased soil saturation, increasing the risk of flooding from this category especially for the Mississippi River.

Below you will find graphics of the precipitation accumulated this winter season (left) and how this amount of moisture compares to normal in percentage (right). These graphics are courtesy of the Midwest Regional Climate Center.

River Conditions

Streamflow analysis from the United States Geological Survey (USGS) indicates the majority of the Upper Mississippi River watershed streamflows are near normal with a few above normal.  The significance of the normal to above average streamflows to flood risk is that a river with higher water levels doesn’t have as much capacity to hold higher amounts of runoff.

Iowa	Illinois	Missouri

Soil Conditions

Soil moisture remains anomalously high across portions of the Quad Cities HSA, including locations along and north of Interstate 80. While precipitation events have waned over the last few weeks, soils remain fairly statuated thanks to above normal precipitation during the winter months. Analysis from the CPC shows soil moisture ranking profile values around 80-95% across much of eastern IA and northwest IL, with these values continuing north into south central WI. Such levels of saturation will not be able to absorb heavy rains, leading to an increased local threat from this category.

Snow Cover and Liquid Water Content

Despite several warm spells across much of the Mississippi River Valley over the past few weeks, analysis from the National Operational Hydrologic Remote Sensing Center (NOHRSC) continues to show a healthy snow cover across much of the Missisippi River basin. Snow depths above two inches were mainly observed along and north a line from Estherville IA to Rochester MN, with the highest depths focused mainly from South Dakota into north central MN and northwest WI and the upper peninsula of Michigan. Here, snow depths range from around ten to forty inches, which is above to well above normal thanks to repeated amounts of snow over the past several months.

Regarding Snow Water Equivalent (SWE), the highest values were located in the aforementioned swath of heavier snow amounts from eastern South Dakota into northwest Wisconsin. Here, SWE values per NOHRSC ranged from around four to eight inches with some locally higher amounts near 10 inches. Values decreased significantly to the south.

Current Snow Depth               Current Snow Water Equivalent

Images courtesy of the National Operational Hydrologic Remote Sensing Center (NOHRSC)

Frost Depth

Frost depths remain rather shallow heading into March into the upper portions of the Mississippi Basin due to an early snowpack as well as above-normal temperatures. The loss of snow cover in February and early March over southeast Minnesota, far northeast Iowa and southwest Wisconsin did lead to a slight increase in frost depth in these areas. Overall, the frost depths in Upper Mississippi Basin range from around 5 to 11 inches, which is much more shallow than normal.  This should allow for a portion of any additional spring rain or snow that may fall across these areas to be soaked into the ground rather than converted to 100% runoff.  

Frost Depths - North Central River Forecast Center

Regional Frost Depths as of March 22, 2023

Ice Jam Flooding

Ice jam flooding is no longer a threat as any lingering ice has melted. 

Crest Timing 

River and Streamflow Information:

• National Weather Service: water.weather.gov
• US Geological Survey: water.usgs.gov/waterwatch
• Corps of Engineers: rivergages.com 

Flood safety and flood insurance information:

• NWS Flood Safety: www.floodsafety.noaa.gov
• National Flood Insurance Program: www.floodsmart.gov

Precipitation, temperature, and soil moisture information:

• National Operational Hydrologic Remote Sensing Center: www.nohrsc.noaa.gov
• NWS Graphical 7-Day Forecast: https://graphical.weather.gov/sectors/uppermissvly.php
• NWS Climate Prediction Center: www.cpc.ncep.noaa.gov
• US Drought Portal: www.drought.gov 

Questions or Comments

If you have questions or comments about this spring flood and water resource outlook please contact:

National Weather Service Quad Cities Hydrology Team
9040 Harrison St
Davenport, IA 52806
Email: cr.dvn-hydro@noaa.gov