National Weather Service United States Department of Commerce
2020 Spring Flood Outlook

 

This Spring Flood and Water Resources Outlook is for the Quad Cities Hydrologic Service Area (HSA), which covers portions of eastern Iowa, northwest and west central Illinois, and extreme northeast Missouri. This includes the Mississippi River from above Dubuque, Iowa to below Gregory Landing, Missouri and its tributaries. The primary tributary river basins include the Maquoketa, Wapsipinicon, Cedar, Iowa, Skunk, and Des Moines Rivers in Iowa, the Fox River in Missouri, and the Pecatonica, Rock, Green, and La Moine Rivers in Illinois.

Probabalistic Hydrologic Outlook

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

Graphical Hydrologic Outlooks

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.

Statistical Hydrologic Outlook

 

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Flood Outlook Overview

A wet fall of 2019 set the stage for elevated flooding potential for Spring 2020. Very wet soil conditions remain across a large portion of the Upper Midwest, with river levels running well above normal for late winter, and well above normal liquid water content in the snow across the northern half of the Upper Mississippi River watershed.

Current conditions suggest that the potential for reaching flood stage is above normal for nearly all rivers across eastern Iowa, northwest and west central Illinois, and northeast Missouri. The highest concern for flooding this season is for the Mississippi River, as current factors suggest reaching flood stage is expected, with high probabilities of reaching major flood stage from Dubuque, IA through Keokuk, IA.

The eventual severity of any flooding will depend on additional precipitation, the rate of snow melt, and spring-time rains. There will also be a risk for long duration flooding this season if soil moisture across the region stays very wet.

To note: even a gradual snowmelt with little rainfall this spring still assures at least minor flooding for the Mississippi River

Key Points:
  • The highest concern for flooding this spring is on the Mississippi River, where the risk for major flooding is much above normal. However, confidence is low at this time in exactly how severe flooding would be at any specific location.
  • Potential for widespread minor flooding is above normal for all rivers across the area.
  • Additional heavy snowfall, a rapid snow melt, and heavy spring rains would increase the threat for more severe flooding. On the other hand, little or no additional snowfall, a prolonged snow melt, and no significant spring rains would decrease the flood threat.
  • If high soil moisture levels persist, the threat for long-duration Mississippi River flooding will increase.

Current and Forecast River Conditions - Advanced Hydrologic Prediction Service (AHPS)

Observed Conditions Forecast Conditions Long-Range Outlooks

 

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.  

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

  • An expansive portion of the Upper Mississippi River watershed is observing extremely wet soil conditions. The flood risk will remain elevated until soils dry out.
  • Snowpack varies across the region. A substantial snow pack is in place across the Upper Mississippi River watershed, while watersheds for local Iowa, Illinois, and Missouri rivers have limited snow cover.

Seasonal Precipitation

For the winter season, December through mid-February, much of the local area has observed near to below normal precipitation. This has led to lower than normal snow cover across eastern Iowa, western Illinois, and northeast Missouri. On the other hand, further north in northern Iowa, Minnesota, and Wisconsin into the headwaters of some of the local rivers, precipitation has been above normal for the winter months. The precipitation this winter has either contributed to building the snow pack, or has kept river levels high as the precipitation either fell as rain or was snow that has already melted, with runoff already making it into the rivers.

The observed winter precipitation raises the risk for flooding on the Mississippi River, as well as rivers that have headwaters up into Minnesota, northern Iowa, and Wisconsin. These rivers include the Rock and Pecatonica Rivers in Illinois, and the Iowa, Cedar, and Wapsipinicon Rivers in Iowa.

 
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

River levels are running above normal for this time of year. They have remained at elevated levels since fall 2019. Following the extremely wet fall months, periods of rain and melting snow have kept the rivers from falling to baseline flows this winter.

The significance of high streamflows to flood risk is that a river with higher water levels will have less space for additional water. As a result, flood levels can be reached with lesser runoff then it would take given normal river levels for late winter/early spring.

 

Iowa Illinois Missouri
Images courtesy of the USGS

 

Soil Conditions

Wet soils have persisted through the winter months as moisture from last fall was locked into the soils during the cold season. There are areas where the soils remained thawed through portions of the winter, but stayed wet due to rain or snow melt with little or no evaporation occurring to allow drying of the soils.

The threat for river rises from snow melt or spring rainfall runoff due to very wet soils is high for the Mississippi River as the entire watershed is experiencing very wet to saturated soils. This means very little runoff will be able to be absorbed by the soils so runoff from both snow melt and rainfall will efficiently move into the river systems. Local watersheds will also have an elevated risk for high runoff from snow melt or rainfall this spring. These watersheds are observing very wet soils across the upper parts of the watersheds, with slightly less moisture in the lower parts.

Image courtesy of the NWS Climate Prediction Center
 

Snow Cover and Liquid Water Content

The snowpack is extensive across the region, with complete coverage extending from southwest Iowa to southeast Wisconsin and all areas north of that line. Snow depths range from a few inches on the southern edge of the snowpack and quickly increase going north, with the majority of the region measuring amounts in excess of one foot. The deepest snow is currently being observed over northern Wisconsin with amounts over 30 inches. These depths are anywhere from 2 to 24 inches above normal for early March.

The water equivalent in the snowpack is quite impressive, with widepread amounts of 2 to 6 inches of liquid in the snowpack. There are even some locations in the region that exceed 6 inches. Along the southern periphery of the snowpack, liquid water content is generally 1 to 3 inches.

The rate that this snowpack melts will be a primary determination of the severity of flooding that occurs.

 

 

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

 

Frost Depth

On average, temperatures have been above normal across the region this winter, with only limited periods of extreme cold. The lack of long periods of extreme cold resulted in below normal frost depths for portions of the Upper Midwest. Shallow frozen ground is being observed across the local area, with frost depths of less than 6 inches being observed for much of Iowa, Illinois, and northeast Missouri.

The depth of frozen ground not only contributes to the flood risk by simply implying any frozen ground will cause efficient runoff from snow melt or rainfall, but the depth of frozen ground is also a factor to how long it might take for the ground to thaw. The longer the ground stays frozen, the longer time it will take before the ground can begin to dry out, thus lengthening the period of time conditions remain at a higher threat for extreme runoff due to frozen ground or high soil moisture.

Frost Depths - North Central River Forecast Center
 

 

Ice Jam Flooding

Warm weather this winter has limited the development of thick river ice. Although colder temperatures in mid-January did cause some ice jam impacts on the Mississippi and Rock Rivers, all rivers observed diminished ice cover by mid-February. Many area rivers are presently observing little or no ice cover. Colder air will likely return yet this winter, so ice development and build-up is still possible. However, without a long period of extreme cold, the risk for development of thick river ice will be low. This keeps the risk for spring break-up ice jams low.

Drought

According to the U.S. Drought Monitor, there are no areas in the Midwest under drought conditions.

Image courtesy of the US Drought Monitor

 

Looking Ahead:

On average, warmer temperatures are expected through the remainder of February and into March, with high probabilities for above normal temperatures through the entire Upper Midwest during the last week of February. With high temperatures averaging around the freezing mark over the following weeks, the impact to the snow pack, and if it will cause river rises will depend on how warm daily highs get, and if lows drop below freezing during the overnight hours.

Rises above freezing during the day, with below freezing temperatures at night would promote a slow snow melt, and be favorable toward limiting the flood risk.

Precipitation outlooks for the next two weeks to three months keep the highest risk for above normal precipitation generally to the south and east of the region, but averaging above normal for much of the Upper Mississippi River watershed.

Above normal temperatures with below normal precipitation would be favorable for a lesser risk of flooding.

8 to 14 day Temperature Outlook 8 to 14 day Precipitation Outlook

 

March Temperature Outlook

March Precipitation Outlook


Additional Information can be found here:

Feb 14, 2020 Webinar Recording

 



River and streamflow information:

Flood safety and flood insurance information:

Precipitation, temperature, and soil moisture information:


Questions or Comments

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

Jessica Brooks
Service Hydrologist
National Weather Service
9050 Harrison St
Davenport, IA 52806
563-391-7094 ext 493
Email: jessica.brooks@noaa.gov