2015 Early Spring Basin Conditions
NCRFC 2015 Spring Hydrologic Outlook will be released February 19, 2015.
Flood potentials analyses are based on current soil and snow conditions combined with a broad spectrum of potential spring weather conditions reflected in the climate record from 1949 to 2012. The analyses contain herein are very general. A quantified risk of flooding with respect to climatology is available through web graphics and tables at NWS Long_Range Flood Risk
The past two weeks have seen a few weather systems cross the Upper Mississippi, Hudson Bay, and Great Lakes basins. Precipitation amounts have been one inch or less north of Interstate 80 with amounts increasing to near two inches in southern Illinois. These amounts are near what can be expected at this time of year.
Temperatures over the past two weeks have been much colder than normal for the end of February. This has preserved what snowpack has accumulated to this point in the season. The cold temperatures have also kept the ground frozen all the way down to southern Illinois. This frozen ground situation will have to be monitored if a significant rain event comes before the soil can thaw in Missouri and Illinois. Rain on frozen ground can be a significant flood threat.
As always, ice jam flooding is possible during the spring melt period. Ice jams have been occurring all winter long as temperature patterns have varied above and below freezing several times this winter. The recent cold wave has allowed ice to reform on many rivers deep into Missouri and Illinois.
Drought conditions remain in place across the Red River Valley and adjacent portions of the Upper Mississippi basin. This will inhibit runoff production from snowmelt and spring rainfall.
All in all, the outlook for spring flooding has not changed much since the report two weeks ago. Portions of the Great Lakes watersheds in the favorable areas for lake effect snow have accumulated a snowpack and have a slightly increased risk for flooding. In addition, the upper Illinois river and its tributaries have experienced periodic flooding this winter and still retain a snowpack. This area of Illinois and northwest Indiana have a greater than 50 percent chance of flooding this spring. Elsewhere in the upper Mississippi watershed the risk for flooding is generally less than 50 percent.
The Hudson Bay drainages of Minnesota and North Dakota are impacted by drought conditions and a lack of a significant snowpack. The chance for flooding in this region is less than 50 percent.
The following basin synopses are the same as the February outlook and include discussion of fall and winter hydrologic conditions.
This will be the final outlook for the spring of 2015.
GREAT LAKES DRAINAGE
The fall season observed above normal precipitation from the western Upper Peninsula to Green Bay, eastward to Sault Ste. Marie and Alpena. Near normal precipitation was recorded from southeast Wisconsin to Saginaw, Detroit and northern Indiana. Soil moisture conditions are consider to be wetter than average in this area. Northeast Minnesota observed below normal fall precipitation and thus has below average soil moisture conditions.
The winter season has brought near to slightly below normal precipitation to most areas. The favored lake effect snow areas of northern Wisconsin, the Upper Peninsula, and areas of western and northern Lower Michigan in the lee of Lake Michigan have seen above normal precipitation. Southeast Michigan is also included in the above normal precipitation category. Snow water equivalent measurements indicate above average amount of water in the snowpack for this time of year in the areas described above.
Winter temperatures have been below average, pushing frost depths to near 3 feet in the western and northern areas while reported frost depths in Lower Michigan are 1 to 2 feet.
UPPER MISSISSIPPI RIVER DRAINAGE
Fall precipitation was near to slightly above normal across Wisconsin, Illinois, Iowa, and eastern Missouri. Fall precipitation was below normal in Minnesota. At the onset of winter, drought conditions had been established over the upper portion of the basin in Minnesota while near average soil moisture conditions prevailed elsewhere. Streamflow conditions as reported by the USGS were near normal for Minnesota, Iowa, and Missouri while being above normal in Illinois and Wisconsin.
Winter precipitation has been below normal across the basin with the exception of a small portion of central Iowa and the headwater basins of the Chippewa and Wisconsin rivers. Reported snow water contents are 3 to 4 inches in extreme northern Wisconsin and generally 1 inch or less elsewhere. Isolated areas of northern Illinois and northwest Indiana show around 2 inches. All in all the snowpack is well below historical averages.
Winter temperatures have been both above and below normal for long periods since November. February is running below normal following a relatively warm January. As a result, soil frost is again building across the basin with 2 to 3 feet reported in Minnesota and Wisconsin… 1 to 2 feet in Iowa and up to 1 foot in Illinois, Indiana, and Missouri. These reports are near normal for this time of year.
When looking at all these factors, the chances for widespread flooding due to snowmelt this spring are low. Much of the basin has normal or below normal risk for flooding. The Kankakee and upper Illinois River have a slightly elevated risk for flooding due to wetter soil moisture condition from periodic melts and having 1 to 2 inches of snow water content.
HUDSON BAY DRAINAGE
Red River of the North River Basin
Late summer and fall recorded below normal precipitation across the Red River Valley, with the highest deficits from normal in the central and southern portions. The winter season has continued with below normal precipitation with the largest deficits recorded in east central and northeast North Dakota. There has been less than 50 percent of normal precipitation in this region. The lack of snow cover and normal to below normal temperatures this winter has allowed the soil to freeze to near historical averages of 2 to 4 feet. With drought conditions having set in during the fall and below normal winter precipitation, the chances for spring flooding are well below average across the basin.
Devils Lake Basin
Fall season precipitation was well below normal. Winter precipitation to date has also been below normal. Current snowpack conditions indicate water contents near one inch in the northern watersheds to one-half inch or less in the Devils Lake area. The lack of snow cover and normal to below normal temperatures this winter have allowed the soil to freeze to near historical averages of 2 to 4 feet. At this time, there is a reduced chance of having total seasonal inflow near the historical normal.
Souris River Basin
The fall season recorded near average precipitation in the western basin and below average precipitation in the east. Fall temperatures were below norm, likely producing below average evapotranspiration. Topsoil moisture is considered near normal with subsoil moisture being above normal. Soil moisture levels become somewhat drier in the eastern portion of the basin. Winter precipitation has been near to slightly above normal with the higher amounts in the west. The winter has seen several thaw periods and thus visual accounts of the basin snowpack indicate below normal conditions.