Overview of NCRFC Region Winter/Early Spring Conditions
There continues to be an above to much above normal chance of widespread flooding in the Upper Mississippi River basin including its headwater tributaries. Overall, the chance of flood risk throughout the remainder of the basins within the NCRFC area is normal to above normal.
Above normal precipitation and below normal temperatures have continued since our initial Spring Flood Outlook. Precipitation in February was 200 to 400 percent of normal with northcentral Wisconsin over 400 percent of normal. Soil moisture ranking from the Climate Prediction Center continues to show mostly above normal conditions across the NCRFC area. These very wet soil conditions have continued to produce normal to above normal streamflows across much of the region this early spring. As we have continued to receive above normal precipitation throughout late winter and early spring, the U.S. Drought Monitor continues to show no drought conditions in our region.
Deep frost continues throughout the area as a result of the continuation of well below normal cold temperatures. With above normal snowfall in February and the beginning of March, combined with the forecast of continued cold temperatures and additional precipitation, at least in the next couple weeks, the elevated flood risk trend continues.
Again, depending on Spring precipitation and temperatures in the coming months, we may see a rapid melt of the snowpack, leading to widespread flooding.
Widespread snow storms have continued across the Upper Midwest since our last flood outlook. As a result, the amount of snow water equivalent across the RFC region continues to be well above normal with widespread liquid equivalents in the 2 to 6 inch range. Persistent cold temperatures have prevented the snow from melting, but over time the snow has become more dense and is becoming ready to melt with warm temperatures and/or rain. The current snow line extends across northwestern Missouri through Davenport, IA to Chicago, IL through Grand Rapids, MI and into Bay City, MI. South of that line, little to no snow remains.
The climate outlook for March suggests the continuation of colder than normal temperatures across the entire NCRFC area with a possibility of transitioning to near normal temperatures. The precipitation outlook seems to keep the above normal chances for additional precipitation. This outlook suggests we may see a delayed snowmelt from these colder than normal temperatures in March. The three month outlook strengthens this suggestion that we may have a near normal temperature and precipitation pattern. If this pattern continues, the likelihood for a rapid melt scenario increases once the warmer temperatures arrive later this spring.
Again, with the fall precipitation saturating the soils, cold temperatures causing deep frost depths and current elevated liquid water equivalents in the snowpack, we continue to have an elevated chance of widespread spring flooding across the RFC area. Spring temperatures and precipitation amounts and patterns, again, will play a critical role in the melt/runoff amounts.
With this outlook, there is an above normal flood risk across Iowa, Missouri, Illinois, Indiana, Michigan, Wisconsin and the Mississippi headwaters in Minnesota. For a detailed discussion concerning the specific watersheds of the NCRFC area, please continue reading below.
GREAT LAKES DRAINAGE
Overall, the flood potential for this area remains above normal. Portions of northern and central Wisconsin, and northern and central Michigan will have an enhanced susceptibility to flooding in the next 90 days based on water in the snowpack combined with saturated and frozen soils.
Temperatures were on average about 10 degrees below normal with mostly two to three times the normal precipitation within the basin since our last outlook. These cold temperatures have continued to bring lake-effect snowfall. Additional snow is forecast in the next few weeks.
The extreme cold temperatures have persisted with ice production, with the Great Lakes having over 74 percent ice cover as of March 3rd. General ice thickness ranges mostly 6 to 12 inches with some of the peripheral shallower edges measuring 12 to 28 inches.
The snowpack remains very deep in the Upper Peninsula thanks to the repeated lake-effect, lending to a widespread snow water equivalent of 10 to 18 inches. The current snow cover is roughly from Holland, MI to Bay City, MI running northward. In Illinois, it extends from around Rockford to the north including all of Wisconsin. Soil moisture remains generally in the 90th percentile. Frost depth ranges from 6 to 12 inches in central to northern Michigan, and generally 6 inches to two feet across eastern Wisconsin with 2 to 4 feet deep in the Upper Peninsula.
Once again, the spring flood potential for this area continues to be above normal. There is widespread snow, giving the risk of flooding a higher probability. This may be even more distressed by the potentially warmer and drier El Nino pattern, if we get an early melt. Some areas have deep frost, which may increase runoff rates due to the frozen ground, especially if the frost does not go out of the ground until later in the spring, or if heavy spring rains are seen.
UPPER MISSISSIPPI RIVER DRAINAGE
Overall, the flood risk for this drainage area remains above to much above normal.
Above normal precipitation and below normal temperatures have continued since our last Spring Flood Outlook. Precipitation in February was as much as 3 to 4 times the usual amount for Minnesota and Wisconsin, and 2 to 3 times from Iowa into Illinois and Indiana. Record snowfall was recorded for many stations in Minnesota and Wisconsin, with above normal levels elsewhere across the basin.
Current snow cover is highest across Minnesota and Wisconsin with depth of 1 to 2 feet common. Further south, snow continues to be more widespread than in a typical year, with at least some snow cover seen all the way down into central Missouri and southern Illinois. Water equivalent in that snow cover is as much as 3 to 5 inches for much of Minnesota, and into central Wisconsin. Snow water of 6 to 8 inches is seen across northern Minnesota and into northern Wisconsin, with even higher amounts in the Arrowhead. Further south, snow water from 1 to 3 inches is on the ground for much of Iowa into southern Wisconsin, with less than an inch south of a line from Des Moines to Milwaukee.
The soil moisture ranking from the Climate Prediction Center continues to show above normal conditions across the area. Streamflow is normal to above normal, and there are still some rivers that have ice activity causing some jamming and flooding. Frost Depth is 2 to 3 feet across parts of Minnesota and Wisconsin, but diminishes further to the south. Depth from Iowa into southern Wisconsin ranges from 6 to 18 inches, with depth less than a foot from Missouri up into southern Michigan.
Taking all of these factors into account, the flood potential for the Upper Mississippi River basin continues to be above to well above normal this spring. High soil moisture and high snow water content on the landscape, combined with a delayed melt and frozen ground late in the season, suggest that when we finally do see warm spring temperatures arrive, the melt is more likely to melt quickly. With ice in the rivers and frozen ground, the resulting runoff looks to generate a high potential for flooding. Also, depending on just how fast the melt occurs, or if we get spring rainfall, we may end up with moderate to major flooding, especially on the mainstem Mississippi River.
We will continue to closely monitor conditions as we move into spring. Conditions over the remainder of March and into early April will be key in determining just how the eventual flooding situation unfolds.
HUDSON BAY DRAINAGE
Red River of the North River Basin
There is an elevated risk of spring flooding along the Red River mainstem, current soil moisture is near normal with winter precipitation well above normal in some areas of the basin.
Late winter and early spring have brought about one and a half to two times the normal amount of precipitation in the Red River Basin, especially for tributaries in northwestern Minnesota.
February and early March temperatures continued the overall well below normal trend this winter. There have also been a few widespread storm systems that brought some additional snow to the region. Basin-average snow water equivalents have increased to around 3.5 inches in the northwest to 4 to 5 inches in the southeastern portion of the basin. Between 150 to 200 percent of normal precipitation has fallen surrounding Minot and near Fargo, North Dakota since November 1st, with near normal amounts since January 1st.
Snow depth remains above normal for the headwater area of west-central Minnesota reaching up into southeast and central North Dakota at about 16 to 24 inches. Northeastern North Dakota to northwestern Minnesota has a current snowpack of near two feet. The Red River is currently experiencing near normal flows for this time of year.
Ice thicknesses on USACE reservoirs continue to be above normal, suggesting similar conditions in the rivers with a higher risk for break up ice jams. The effects of ice jams are not included in any of the long range probabilistic outlooks. Red River ice thickness is above normal based on February measurements with thickness ranging between 22 and 40 inches.
Frost continues to be deeper than normal. Frost depths of 3 to 4 feet have persisted with the frigid temperatures. This combination of wet soils and deep frost continues to lead to a higher potential for runoff due to the frozen ground, especially if the melt is sudden and accompanied by rainfall or more snow accumulates between now and the melt.
Souris River and Devils Lake Basins
The overall risk for flooding in these basins continues to be near to slightly above normal.
It has been extremely wet in February and early March across most of North Dakota, with precipitation between 175 and 300 percent of normal in the last 30 days. With the recent above normal snowfall, the abnormally dry designation in the U.S. Drought Monitor has been removed for the entire state.
Colder than normal temperatures have dominated in February and so far in March, continuing the trend of below normal temperatures this winter. Temperatures have ranged from 18 to 22 degrees below normal throughout North Dakota and Saskatchewan, Canada.
For the Souris basin, there continues to be a slightly below normal risk of flooding above Lake Darling, with risk increasing downstream to near normal from Minot to Bantry, North Dakota to an above normal risk downstream through Westhope, North Dakota.
Modeled snow water equivalents range from below normal in most of Saskatchewan to above normal in the North Dakota portion of the basin, especially the Willow and Deep River basins. Values range from 1.5 to around 4 inches of water equivalent and agree well with recent surveys in Saskatchewan and North Dakota.
River ice regularly contributes to ice jam flooding along the Souris. Releases from Lake Darling are controlled in the spring in order to mitigate impacts due to break up ice jamming.
In the Devils Lake basin, dry conditions have transitioned to wet starting late January. There has been little change in the soil moisture conditions since the last outlook. With current snow conditions, the lake is expected to rise slightly higher than normal by about a foot and a half. There does remain some uncertainty, however, with how the previous very dry soils will respond to the spring melt of the fairly substantial snowpack.
Frost depths continue to be generally deeper than normal. Additionally, there were a couple of melt cycles and rain events earlier in the winter, some of the water ended up frozen in the top layer of soil and in artificial drainage networks. This could contribute to frozen ground impacts, depending on the progression of the spring snow melt. Flood risk due to river ice and frozen ground impacts are not well captured in the modeling and outlook products.