2014 Early Spring Basin Conditions
Hydrologic conditions in the NCRFC area have not changed significantly since the issuance of the last outlook two weeks ago. (Detailed discussion of specific basin hydrologic conditions from the February 20 issuance of this product can be referenced below ).
Precipitation during the last two weeks has been within climatological normals across the area, causing little change to our probabilistic distributions this issuance. Ice remains a significant complication and flooding risk factor across northern Illinois, northern Indiana and Lower Michigan, where the rainfall and snowmelt event that occurred at the time of the last outlook caused minor and moderate flooding. A return to below normal temperatures has refrozen a lot of the breakups in place, and ice will start to move again when temperatures moderate. Ice is also significant in other areas of the region, with portions of the Upper Mississippi mainstem seeing ice approaching record thickness.
Additionally, frost depths across the region are deeper than what is usually observed at this point in the season. It remains to be seen how this will impact runoff rates. A fast melt will have increased runoff rates as infiltration will be limited. An extended melting period will allow melt water to slowly work its way into the soil and aid in the thawing process. At this time, meteorological models are indicating that there is little chance of a rapid and significant warm-up within the next few weeks.
Flood risk due to ice and frozen ground enhanced runoff are not captured well within our hydrologic model simulations, so risk in areas where these complications exist may see higher levels than what is captured in our current probabilistic distributions.
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
GREAT LAKES DRAINAGE
The Great Lakes watersheds of Minnesota, Wisconsin and Michigan are generally characterized by normal to above normal soil moisture conditions going into the December freeze-up. Winter precipitation has been up to 75 percent above normal in the Lake Superior basins and near to 25 percent above normal in the Lakes Michigan and Huron basins. Snow cover is deep across the region with water contents ranging from 2 to 4 inches in western Lake Michigan basins to 3 to 6 inches across Lower Michigan and northern Indiana. Snow water contents in the Lake Superior basins are 4 to 6 inches in Minnesota and northern Wisconsin, and 2 to 8 inches across Upper Michigan. Ground frost west of Lake Michigan is 2 to 4 feet, while east of the lake, frost penetration is negligible across the western half of Lower Michigan, increasing to near 6 inches in central Michigan and northern Indiana. The deepest frost in Lower Michigan is in the east where up to 20 inches has been observed.
The southern Michigan and northern Indiana watersheds have a moderately increased risk for flooding with a high risk for flooding in the Grand basin, especially from Ionia to Lake Michigan. Flood risk is near normal for the Minnesota and Upper Michigan watersheds. Flood risk is slightly above normal in the Wisconsin and northern Lower Michigan watersheds.
UPPER MISSISSIPPI RIVER DRAINAGE
The Upper Mississippi River watershed is generally characterized by near to below normal soil moisture conditions going into the December freeze-up. Winter precipitation has been above normal across central Minnesota and northwest Wisconsin with somewhat below normal precipitation observed across the rest of basin all the way down to St Louis. Snow cover is present across the entire watershed. Snow water contents across Minnesota and Wisconsin range from 2 inches in the south to 5 inches in the north. Snow water contents across Iowa range from one-half inch in the Des Moines basin, to 2 inches in the eastern basins. Across Illinois and Missouri, snow water contents are 2 to 3 inches in the Chicago area, decreasing to 1.5 inches from Moline to Peoria, and around one-half inch in and around St Louis. Due to the persistent cold temperatures across the Midwest this winter, the ground has frozen down to 3 feet across Minnesota and Wisconsin, 2 feet across Iowa and northern Illinois, and 1 foot of frost is observed across eastern Missouri and southern Illinois.
There is a somewhat elevated risk of spring flooding across much of Wisconsin, the northeastern quarter of Illinois and northwest Indiana. Risk is below normal in the south and west portions of the basin, increasing to near normal across eastern Iowa, western Illinois and much of Minnesota. The mainstem Mississippi river has a climatologically normal risk of minor flooding with a diminished risk for moderate or higher level flooding.
HUDSON BAY DRAINAGE
Red River of the North River Basin
The Red River of the North has a snow cover from 1 to 3 inches of water content. The water contents are highest in the northwest Minnesota watersheds. Soil moisture levels are near to somewhat above normal across the southern valley and near to somewhat below normal across the northern valley. Frozen ground depths are reported to be 2 to 3 feet. Surface storages such as potholes, marshes and lakes are at normal capacities having seen some refill in 2013 after the drought of 2012.
There is a somewhat elevated risk for minor flooding and a near normal risk for moderate or higher level flooding across the southern tributary rivers and mainstem Red. Across the northern tributary rivers there is a normal to slightly below normal risk of flooding, while on the mainstem there remains an elevated risk for minor flooding and normal flood risk for moderate and higher levels.
Devils Lake Basin
Snow water equivalents across the Devils Lake basin range from 2 to 2.5 inches; which is near normal for this time of year. Soil moisture conditions and 2 to 4 feet ground frost penetration are at seasonally typical levels. At this time the outlook is for a relatively normal runoff volume into Devils Lake this year.
Souris River Basin
The Saskatchewan portion of the basin has observed a relatively dry fall and winter to date. Runoff is expected to be below normal. The North Dakota side of the basin saw above normal fall precipitation and relatively wet soils going into freeze-up. Snowfall has been near normal with snow water contents of 1 to 2 inches. Frozen ground depths are 3 to 4 feet. There is a normal risk for spring flooding in the Souris basin from Sherwood, ND to Velva, ND. Downstream from Velva to the Canadian border there is an increased risk of minor to moderate flood levels and a normal risk for floods above the moderate level.
This is the first of two spring flood outlooks. With a few more weeks of winter still to come, flood potential conditions will likely change.