Overview of NCRFC Region Winter/Early Spring Conditions
There is a significantly elevated chance of flooding in the Upper Mississippi River drainage area and the Hudson Bay drainage area, particularly along the Red River of the North. Overall, 101 forecast points show a 50% or greater chance of moderate to major flooding, with the greatest concentration of flood risk along the Mississippi River and Red River of the North. Tributaries to these basins also have a significantly elevated flood risk. While the flood risk in the Great Lakes drainage basins is also elevated, it is mostly of minor to moderate flooding.
Above normal rainfall occurred during last calendar year (125 to 150% of normal). In the early summer the NCRFC received near normal amounts of precipitation, climbing to above normal in the later months. The fall was extraordinarily wet in September and October, with precipitation accumulations as much as 300% of normal over most of the NCRFC. November was comparatively dry, with normal to slightly above normal precipitation accumulations. As a result soil conditions going into the winter were saturated and currently stand in the 95th to 99th percentile over the most of the NCRFC. During the winter months, the pattern of above normal precipitation continued. The accumulated precipitation in North Dakota is as high as 300% of the mean with 150%-200% of the mean seen across Minnesota, northern Wisconsin and the Upper Peninsula.
Widespread coverage of significant snow across the NCRFC basins began at the end of November. Five large scale snowstorms deposited above normal amounts during the late November to January timeframe. While the fall and early winter showed a concentration of precipitation across the northern areas of the NCRFC, in the latter half of January and early part of February, precipitation patterns shifted to the south, driving accumulations in Iowa, Illinois and lower Michigan. Currently 1-4" of snow water content exists across eastern North Dakota, Minnesota, northern Wisconsin and the Upper Peninsula with as much as 6-10" of snow water content found in the basins near Lake Superior.
Very wet soil conditions combined with the late summer and fall rainfall have driven well above normal streamflows across the entire NCRFC. Currently, the U.S. Drought Monitor shows no drought conditions within our region. As far as recent temperatures go, a widespread arctic blast came across the Midwest in mid-November, but December was above normal. From January to February 13th, above normal temperatures have prevailed driving a denser snowpack through a cycle of daytime melting and nighttime re-freezing.
Generally, frost depths are near normal throughout the area. This is a result of the mid-November cold snap that occurred with little to no snow cover on the ground at the time. Most soils were very wet and when it did snow it provided an insulating layer preventing deep freezing of the soils. With the areas of little to no snow cover, the recent warmer than normal temperatures have led to shallow frost depths.
The outlook for March suggests slightly colder than normal temperatures and slightly higher than normal precipitation across the entire NCRFC area. This suggests we may build a greater snowpack and have a below normal snow melt pattern. While there is a great deal of uncertainty in this outlook, it reinforces the likelihood of a rapid melt scenario once the warm temperatures arrive later this spring.
With 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 elevated water content in the snowpack, we have a well above normal chance of widespread spring flooding across the NCRFC area. As usual, spring precipitation and temperature patterns in the coming months will determine the snowmelt rate and runoff timing. Based on these conditions we expect a high probability of seeing widespread flooding.
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 is well above normal.
Fall began with temperatures above normal throughout September, but turned much colder than normal for October and November. December was milder with slightly above average temperatures and a pattern shift to well above normal temperatures for January and the beginning of February across the Upper Mississippi River basin. Overall, January and early February temperature readings were 2 to 8 degrees above normal. This recent temperature pattern has allowed snow to become more dense and ready to melt with various amounts of snowmelt already occurring, which is very unseasonable for late winter/early spring. In fact, temperatures rose to 53 degrees in some areas in southern Minnesota and southern Wisconsin. This is about 20 degrees above average.
Generally, the fall was abnormally wet across the drainage area. Both September and October were extremely wet in southern Minnesota, southern Wisconsin, northern Iowa and northern Illinois with well over 200 percent above normal precipitation. November saw a drier pattern with near normal amounts, then back to over 2 times the normal in December for most of Minnesota and Wisconsin, though precipitation accumulations the southern part of the drainage area were near normal during this period. Starting in January, the precipitation pattern shifted to the south, driving up accumulations in Iowa, Illinois and Michigan but remaining at near normal levels in the north.
Snowfall across southern Iowa, the northern half of Missouri, and western and northern Illinois has been near to below normal so far this winter. However, as of February 4th, snowfall has been 1 to 3 times the typical amount for the winter season in the north. Current snow cover is highest in an area from eastern North Dakota, through northern Minnesota and into northern Wisconsin. Depths of 18 inches to 2 feet are common. Farther south, snow cover is about the normal distribution for this time of year with the snow line extending from Des Moines, Iowa to LaCrosse, Wisconsin.
Water content in the snow in the northern portions of Minnesota and Wisconsin is near 8 inches. Liquid equivalent of 3 to 6 inches is prevalent over a widespread area from North Dakota and Minnesota over to Wisconsin. Snow amounts of mostly a trace extend from Iowa into southern Wisconsin. Most of the snow, if not all, has melted from Missouri across most of Illinois and Indiana. Overall the amount of snow water content is well above normal in the northern regions of the Upper Mississippi drainage area and with the shift in precipitation patterns beginning in January it is possible that amounts in the southern area will rise through the end of winter.
Late December and mid January storms brought significant rain and snow to much of the region, along with a surge of warm temperatures. This thaw produced some melt, and the added rainfall did result in some minor flooding issues for portions of Iowa, Illinois, and Wisconsin, as rainfall amounts of 1 to 1.5 inches fell on frozen ground for both occurrences. With the above normal temperatures in both January and February, a sizable amount of snowpack melted, contributing to higher flows. The resulting rapid runoff led to some streams rising out of their banks, and ice to break up for a few localized ice jams. These and future ice jams will be an aggravating issue for future high flow events this spring. Refreezing of soils after the melt in January could pose a higher flood risk this spring.
Soil moisture conditions are well above normal across Minnesota and Wisconsin which are in the 99th percentile. Iowa and northern Illinois soil profiles are very wet too and are in the 90th percentile and wetter. Northern Missouri is also wet and is in the 80th percentile. Generally, as you progress south, there is an decrease in soil moisture, which is opposite of last year.
As a result of the above normal precipitation last year and especially the very wet fall months, streamflow across the region is running much above normal and even in the "high" category according to the U.S. Geological Survey. "High" indicates that the estimated streamflow is the highest value ever measured for that day of the year.
This year frost depths in the drainage are normal to below normal. Many areas are showing well below normal frost depths for this time of the year. This is a result of a combination of above normal wetness in the soil profile and snow insulating the ground prior to the deep freeze. Most depths are in the six inch to two feet range across much of Minnesota and into Wisconsin. Some reports are less than three inches in depth. There were several reports of farmers struggling to get in a very late harvest from the wet fall because the ground did not freeze, sinking equipment in the fields. Generally southern IA, northern Missouri and across Illinois, frost penetration is minimal to none.
Overall, the flood potential for this spring is well above normal for the Upper Mississippi River drainage. There is a persistent 50% or greater chance of major flooding along the Mississippi river down to lock and dam 19, and a persistent 50% or greater chance of moderate flooding from lock and dam 19 to St. Louis. We will continue to closely monitor conditions as winter closes and we enter the spring snow melt season. Conditions over the next 4-6 weeks will be key in determining just how the flooding situation will evolve.
GREAT LAKES DRAINAGE
Overall, the risk of flooding is above normal for the Great Lakes Drainage area. Most of the risk is of minor flooding with isolated points of moderate flooding possible.
Precipitation patterns in the Great Lakes were generally wet through the fall and early winter. In September, October and December, northern Minnesota, Wisconsin and the Upper Peninsula received as much as 300% above normal precipitation. Starting in January the precipitation pattern shifted to the south and has begun to drive up accumulations in lower Michigan. November temperatures were on average 5 degrees below normal. That colder than normal trend did not persist with December, January and early February generally 2-8 degrees above normal. These conditions favored lake effect snow. Currently basins bordering Lake Superior show as much as 8 to 12 inches of snow water equivalent. In the southern areas of the Great Lakes drainage area, the snow water equivalent is much lower. The southern half of lower Michigan and the southeastern corner of Wisconsin show 0-1" of snow water equivalent, with those values increasing northward in both states.
As with the rest of the NCRFC area, a wet year and particularly wet fall has driven 95th-99th percentile soil moisture and elevated stream flows going into the winter. Colder temperatures in November and sporadic cold snaps in December and January drove some ice production that further elevated river levels. In the Great Lakes themselves, however, ice production has been limited and ice cover is far less than what was observed in 2019 and 2018. Currently Lakes Superior and Michigan both show less than 15% ice cover. Lake Huron has more ice cover at just under 30% but this is still far less than what has been seen in previous years.
In the Great Lakes drainage basin lake levels themselves present a serious issue. Lake Michigan-Huron is forecast to be above monthly record levels through June. Superior is forecast to be just below monthly record levels through June. Lakes St. Clair, Erie and Ontario are all forecast to be below record highs through June.
Frost depth is 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 2 to 9 inches.
Overall, the spring flood potential for this area is above normal due saturated soil conditions and heavy snow layers in the north. There is a greater than 50% chance of widespread minor flooding throughout the Great Lakes Drainage area with the potential for greater than 50% chance of moderate to major flooding observed at isolated locations. One complication in this drainage basin comes from the historic lake levels. Any wind events that set up across Lake Michigan and blow towards the shore of Wisconsin cause backwater events. Should we get a combination of widespread rain/melt and one of these shoreward wind events we can expect wide spread flooding issues of the Fox, East and Oconto rivers.
HUDSON BAY DRAINAGE
Red River of the North River Basin
Going into the fall months, precipitation was well above normal in September and October (200 to 400 percent of normal) and below normal in November. Over the winter months, precipitation has been above normal in eastern North Dakota and Minnesota. Given the elevated precipitation, most streams and rivers in the area went into the winter running at historically high baseflows.
November saw temperatures 2 to 3 degrees below normal. December brought normal temperatures to the basin while January brought temperatures ranging from 1 to 4 degrees above normal with early February following suit.
The month of December brought above normal snow water content. Early to mid January brought melt to the snowpack and by mid January above normal liquid equivalent dominated the basin. Snow depth is currently above normal between Fargo and Grand Forks at a depth of 18 to 20 inches with the remainder of the basin in the 12 to 14 inch range. Current water content in the snow in the Red River of the North basin is between 1 to 5 inches. An important point here is that we had an unusually early snowpack begin to develop at the beginning of December. Currently we are at 300%-400% above normal for precipitation accumulation from September through February in a solid stripe across Fargo and in the southern drainage basins of the Red River of the North.
Baseflows in the Red River basin were historic going into the winter, Ice thickness on USACE reservoirs is normal to below normal, suggesting similar conditions in the rivers resulting in a low to medium risk of break up ice jams, despite the high flows. The effects of ice jams are not included in any of the long range probabilistic outlooks.
Frost depths are generally shallower than normal this winter with depths of 18 inches to 2 feet being reported. Summer and fall rains have contributed to an abundance of soil moisture. The combination of above normal snow water content and deeply saturated soils suggests a high risk of large amounts of runoff, especially if the melt is sudden and accompanied by rainfall. Under current conditions, the flood risk in the Red River of the North is significantly elevated, with most forecast locations showing a greater than 50% chance of moderate to major flooding.
Souris River and Devils Lake Basins
As a result of the abundance of moisture last year the most current U.S. Drought Monitor map shows no drought classification anywhere in North Dakota.
Fall precipitation was well above normal in both September and October with a change to a below normal pattern for November and December. January and early February brought just below normal snowfall. Overall, the wetness of the soils should be the dominating factor in determining the flood risk in this region.
While November was 1-2 degrees colder than normal, temperature patterns shifted to 1-2 degrees warmer than normal starting in December. That pattern has persisted through mid-February.
In the Devils Lake basin, wetter than normal soil moisture conditions prevail. The unusually wet fall conditions have pushed baseflows up in the basin, resulting in a cold season rise of 0.7 ft in lake levels from September to February. This is highly unusual. With that rise and the wet conditions seen in the fall, there is a 90% chance of 1.5\\' rise and a 50% chance of a 2.5\\' rise in lake levels through September of 2020.
For the Souris basin, there is a below normal risk of flooding above Lake Darling, with risk increasing downstream below Minot to an above normal risk at Westhope. With reservoirs in Saskatchewan at or below February 1 target levels no further drawdowns are expected and there is capacity to store runoff at Rafferty and Grant Devine
Snow water content rankings are below normal in most of Saskatchewan and in the North Dakota portion of the basin, with snow water content of generally less than an inch throughout the Souris basin.
Frost depths are generally near to below normal this winter. Additionally, there were a couple of melt cycles and rain events throughout the winter and some of the water ended up frozen in the top layer of soil and in artificial drainage networks. Generally, soil moisture should be the dominant contributor to runoff rates during the progression of the spring snow melt.
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.
Flood risk due to river ice and frozen ground impacts are not well captured in the modeling and outlook products.
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High Plains RCC
US Drought Monitor