Overview of NCRFC Region Winter/Early Spring Conditions
The chance of flooding in the Upper Mississippi River drainage continues to be significantly elevated. This assessment includes the Hudson Bay drainage and the Red River of the North basin as well, with both basins continuing to have a significantly elevated chance of flooding. Overall, 68 forecast points show a 50 percent or greater chance of moderate to major flooding within the next three months (a significant decrease from the last update where it was 103). The overall number of forecast points may change slightly as a few last minute changes on the Red River of the North will be made after this issuance due to complications of the snow melt, current conditions assessment and technical issues. The Upper Mississippi River and Red River of the North continue to have the greatest concentration of flood risk as far as the mainstem rivers go. Tributaries to these basins continue to have a significantly elevated flood risk with the risk increasing as it progresses downstream. While the flood risk in the Great Lakes drainage basins continues to remain elevated, potential minor to moderate flooding is expected. The general trend of little to no precipitation over the past few weeks has lessened the overall flood risk across the area, but until all snow is gone and vegetation is established, the flood risk remains.
Soil conditions have remained saturated throughout the winter and into spring. Soil wetness remains mostly in the 95th to 99th percentile over the NCRFC area. Iowa and northern Missouri are the exception as the snow cover is long gone and fields have dried out quite a bit in late February and early March, the soil moisture ranges in the 70th to 90th percentile in those areas. It has been much drier than normal with the exception of near normal precipitation in the northern tier of Minnesota and the Upper Peninsula of Michigan since our latest flood potential outlook update. To demonstrate how dry the early spring has been, most of the NCRFC area has been in the 2 to 50% of normal range. The short term outlook calls for mostly widespread light precipitation with the concentration over central Iowa and Missouri over the next few days.
With the recent dry and warm pattern, a significant amount of snowcover has melted. Current snow water content has decreased and is currently 2-4 inches across eastern North Dakota, Minnesota and northern Wisconsin. The Upper Peninsula remains in the 8 to 12 inch range with as much as 18 inches of snow water content found near Houghton, Michigan by Lake Superior.
Of the reporting stations, well above normal streamflows remain across the entire NCRFC boundary. The U.S. Drought Monitor shows no drought conditions within our area as wet soil conditions have continued to prevail. Temperatures have remained to be above normal since our last update. On average, the temperatures have been one to three degrees above normal across the area. Temperatures have also shown a two degree maximum temperature average above normal in early March. The mid-term forecast has changed to near normal temperatures and slightly above normal precipitation for the third week of March.
Generally, frost depths remain near to below normal throughout the area. The snow line has been progressively migrating northward. Recent warmer than normal temperatures have caused a lot of melting and ground thawing, allowing frost depths to become shallower or melted out altogether. Again, with the continuing warm temperatures during the day and cool to freezing temperatures at night, frost depths should continue to play a lesser role in the spring flood potential. Looking at the mid to long term temperature forecast, a deep freeze is not expected which would prolong the remaining snow melt and potentially worsen the flood risk. The most likely scenario would be persistent well above normal temperatures coupled with significant spring rains which would elevate the flood risk.
The climate outlook for the latter part of March suggests a much higher than normal temperature pattern, but a near normal chance of overall precipitation. For the three-month outlook of March, April and May, near normal temperatures and slightly above normal precipitation is expected. With near to above normal temperatures forecast in the next few weeks, significant snow melt should continue. While there is a great deal of uncertainty in this outlook, it reinforces the likelihood of a fairly rapid melt scenario.
To summarize the overall flood risk, the main contributors are last year's above normal precipitation pattern deeply saturating the soils, near normal frost depths, high winter flows in the rivers and streams and current water content remaining in the snowpack. These factors will continue to produce a well above normal chance of widespread spring flooding across the NCRFC area. As usual, spring precipitation and temperature patterns in the coming number of weeks will determine the snowmelt rate and runoff timing. Based on current and forecast conditions we expect a high probability of seeing widespread flooding across our area.
For a detailed discussion concerning the specific watersheds of the NCRFC area, please continue reading below.
UPPER MISSISSIPPI RIVER DRAINAGE
Overall, the flood risk for this drainage area including its tributaries continues to be well above normal.
Nearly 5 to 25% of normal precipitation fell across the Upper Mississippi River basin since the latest update to the Spring Flood Outlook. Mid-western Minnesota was the driest area with only 1 to 2% of normal precipitation. All across Iowa, southern Wisconsin, southern Minnesota and northern Illinois saw well below normal precipitation. As far as temperatures go, most of the area was 2 to 3 degrees above normal across Minnesota, Wisconsin, northern Iowa and northern Illinois. Northern Indiana was just above normal in this timeframe.
These above normal temperatures have brought on the spring melt. Widespread melt has occurred and is continuing. Soils remain saturated, but with minimal frozen ground conditions, some areas have been able to absorb this snow melt. Ponding is continuing, and low lying areas are filling with melt water. Streams are seeing rises and iced areas are breaking up with some break up ice jams causing flooding.
Current snow cover extends across central Minnesota to central Wisconsin. Hutchinson, MN and Marshfield, WI appears to be the southern extent of the snow line. The average depth is about 6 to 8 inches with deeper amounts in the Peninsula and northern Wisconsin areas where depths of 18 inches and greater are common. This continues to be near to above normal for this time of year.
Water content in the snow in the Mississippi River contributing portions of Minnesota and Wisconsin is 2 to 5 inches on average. A recent report of 1.5 to 2 inches of liquid equivalent was reported across south central WI and in the north central parts of WI, reports of 2 to 5 inches have prevailed. Across central MN, liquid equivalents ranged in the 2 to 3.5 inch range. Overall the amount of snow water content remains to be above normal in the northern regions of the Upper Mississippi drainage area.
Soil moisture conditions as reported from the Climate Prediction Center continue to be well above normal across Minnesota and Wisconsin which are mostly in the 95th percentile. Iowa and northern Illinois soil profiles remain wet, but are slowly drying out and are in the 80 to 90th percentile for soil moisture. Northern Missouri ranks in the 70th percentile and is showing a drying out as well. Again, with dryness prevailing, the southern portion of the Upper Mississippi River basin is drying out. As we see soils dry out especially in the northern part of the basin, melt water and ponded water will be able to be absorbed, lessening the flood risk.
Monthly average streamflows across the Upper Mississippi River basin remain above to much above normal with many stations in the "high" category according to the U.S. Geological Survey. These stations are located mostly within Minnesota, Wisconsin and northern Iowa. "High" indicates that the estimated streamflow is the highest value ever measured for that day of the year. Frost depths within the drainage remain to be near to below normal.
Current warm temperatures and snow melt have created a few break up ice jam flooding situations, primarily in Minnesota on the Cottonwood, Minnesota and Rush Rivers. The Cottonwood River near New Ulm broke its banks on March 4th going into Major flood where it destroyed a nearby street.
Overall, the flood potential for the spring melt remains well above normal for the Upper Mississippi River drainage, especially on the mainstem rivers. There is a 50% or greater chance of major flooding from Dubuque, IA along the Mississippi River down to Burlington, IA and a 50% or greater chance of moderate flooding from Keokuk, IA on down to St. Louis, MO. The major flood potential has decreased from St. Paul, MN to near La Crosse, WI since our last update.
We will continue to closely monitor observed and forecast weather conditions as we continue the spring snow melt season. Conditions over the next few weeks or so will be key in determining just how the flooding situation evolves.
GREAT LAKES DRAINAGE
Overall, the flood risk is near to above normal for the Great Lakes Drainage area. Most of this risk is minor flooding with isolated points of possible moderate flooding.
Since February 26th, precipitation has continued to be mostly dry with normals ranging between 2 percent of normal and near normal in eastern Wisconsin, Michigan, northern Illinois and northern Indiana. The exception to this is a portion of the Upper Peninsula above Lake Michigan, which has had normal to above 150% of normal precipitation for this timeframe.
Currently, basins bordering Lake Superior continue to show as much as 8 to 12 inches of snow water equivalent, which has not changed since our last update. Some areas of the basin are showing upwards of 18+ inches of liquid equivalent. The current snow line is just above Green Bay, WI and just north of Big Rapids, MI. Nearly 4 to 8 inches of snow water equivalent remains between Bear Lake and Gaylord, MI.
Soil moisture has remained extremely wet with values in the 95th to 99th percentile. The abundance of rainfall last year, has caused elevated streamflows throughout the winter and early spring. Temperatures since our last outlook update have shown a 2 to 4 degrees warmer than normal trend. This winter and spring has demonstrated limited ice cover on the Great Lakes and is far less than recent years observations. Currently, Lakes Superior and Michigan both show less than 8 percent ice cover. Lake Huron has more ice cover at about 16 percent, but still is far less than what has been seen in previous years.
Frost depth continues to be 3 inches or less over lower Michigan. Deeper frost is present across eastern Wisconsin, northern Minnesota and the Upper Peninsula with values generally ranging from 3 to 12 inches.
Overall, the spring flood potential for this area continues to be above normal due to the saturated soil conditions and the heavy/wet snowpack in the north. There continues to be a greater than 50% chance of widespread minor flooding throughout the Great Lakes Drainage area with the potential for a greater than 50% chance of moderate flooding observed at one location on the Tyler Forks River near Mellen in the Bad River Basin. This moderate risk has decreased from 5 locations two weeks ago.
HUDSON BAY DRAINAGE
Red River of the North River Basin
There remains an elevated risk of spring flooding along the Red River of the North mainstem. This risk remains even though precipitation since our last February 26th update until now has been very dry (mostly 2 to 10 percent of normal) across eastern North and South Dakota and western Minnesota. Again, this elevated risk is a result from the well above normal soil moisture along with above normal snowpack remaining across most of the basin. The current snow water equivalent across most of the basin has lowered to 2-4 inches. Recent windshield surveys of the south valley, above Wahpeton, have shown little to no water ponding and about 50 to 80% of the snow cover gone. Most of the water has been observed to have soaked into the ground. This is good news, but caution should be placed as there has yet to be more melt up in the mid to northern part of the Red River of the North valley.
Since our revised outlook, temperatures have been about 2 to 3 degrees above normal throughout the basin. These warm temperatures that have spanned for a month or so now, have condensed and have begun the snowpack melt. As noted above, the warm weather has caused significant melt. With the current forecast, the melt process is expected to continue.
Current snow depth ranges from 8 to 18 inches across the valley. Snow depth between Fargo and Grand Forks remains to be in the 12 to 16 inch range. The remainder of the basin is in the 8 to 12 inch range.
Again, river flows in the Red River basin were above normal going into winter. Ice thickness on U.S. Army Corps of Engineers reservoirs remains to be normal to below normal, suggesting similar conditions in the rivers resulting in a low to medium risk of break up ice jams. The effects of ice jams are not included in any of the long range probabilistic outlooks.
Frost depths remain generally shallower than normal. These shallow depths may play a role in allowing more water to infiltrate into the soil. The combination of above normal snow water content and deeply saturated soils will continue to produce a high risk of large amounts of runoff. The near term risk of rainfall accelerating the melt and worsening the flood risk is low. Under current conditions, the flood risk in the Red River of the North is elevated, but potentially could weaken if the melt water absorbs into the soil or not. Most forecast locations continuing to show a 50% or greater chance of moderate to major flooding.
Souris River and Devils Lake Basins
For the Souris basin, there continues to be a below normal risk of flooding above Lake Darling, with risk increasing downstream below Minot to an above normal risk near Westhope, ND.
Precipitation has been on the dry side in the Souris basin (10 to 50% below normal), but has faired a little better than the Red River of the North valley since our latest update. Temperatures have been well above normal; mostly 9 to 11 degrees above normal in this same timeframe. The current snow cover extends mostly east of Rugby, ND with the majority of the snow in Westhope, Bottineau and Dunseith, ND. Most liquid equivalent amounts in these areas are under an inch. These snow amounts are below normal for this time of year.
The wetness of the soils could play a factor in determining the flood risk in this region. The soil moisture continues to range in the 90th to 95th percentile for most of the basin and depending on how and when the snow melts, it could worsen flooding conditions and impacts.
Reservoirs in Saskatchewan are currently at or below March 1 target levels, so no further drawdowns are expected. There continues to be capacity to store excess runoff at Rafferty and Grant Devine reservoirs. The Saskatchewan portion of the basin has continued to be drier than the North Dakota side through the fall/winter and early spring with soil moisture conditions indicating capacity for infiltration of snowmelt runoff.
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, wetter than normal soil moisture content continues. Much below normal precipitation has continued to persist across the area. Current snow water equivalent across the basin is an inch to over 2 inches. The unusually wet fall conditions have pushed baseflows high in the basin, resulting in a winter season rise of about 0.7 feet from September to date. The current lake level is approximately 1,449.0 feet. The lake level probabilities for summer are having a 90% chance of a 1.7 foot rise and a 50% chance of a 2.2 foot rise through September 2020.
Frost depths continue to be near to below normal. Generally, soil moisture should be the dominant contributor to runoff rates during 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.
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US Drought Monitor