AccuWeather.com

By Alex Sosnowski, Expert Senior Meteorologist

Mar 19, 2010; 5:45 AM ET

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While many rivers over the northern Plains are rising to familiar levels of the past couple of years, some communities are seeing rivers rise to new heights as snowmelt accelerated this week.

Temperatures surged into the 40s and 50s over the region during the first part of the week.

While the massive snowpack over the northern Plains has shrunk substantially, there are still hundreds of square miles where the snow contains from 4 to 8 inches of water.

New Weather Impacts

AccuWeather.com Meteorologists remain concerned that freeze and thaw cycles, combined with several storms with rain and eventual runoff from new snow over as many weeks, may eventually add to the flooding problems.

The storm affecting Colorado and the central Plains will miss much of area experiencing the worst flooding. However, some snow will fall over portions of flooded Iowa.

This and other storms to follow could result a prolonged recession of flood waters or eventually in new rises of rivers and streams in some areas.

The upcoming pattern over the next month points toward several storms or more over the central and northern Plains with rain and/or snow.

As a result, the prediction of exact river levels in the area and downstream locations in the weeks ahead are very complex and uncertain.

Because of its size and massive watershed, the central and lower Mississippi River from Missouri and Illinois on south could remain above flood stage for months. The river was just beginning it rise in the Deep South this week.

The Situation Now

Some rivers, such as Red River of the north, will remain at or above flood stage for weeks. Generally the larger the river the longer the flooding cycle.

There have never been back-to-back years of major to record flooding along the Red River in its 110-year history according to National Oceanic and Atmospheric Administration hydrologists.

At Fargo, the Red River may come within a couple of feet of the record mark of 40.8 feet set just last year. The river is forecast by the National Weather Service to crest near 38 feet by early next week.

The Red River, which flows from south to north, will rise significantly to major flood levels above Fargo in the weekend and beyond.

Portions of the James (of the northern Plains) and Little Sioux rivers have set record levels this week.

Officials are closely watching the levees in the Des Moines, Iowa area. The Des Moines and Raccoon rivers around Des Moines were at moderate to major flooding levels at midweek and were expected to remain at this mark well into next week following a crest over the next several days.

In areas where there is still substantial snow on the ground, such as much of North Dakota and northern South Dakota, ice jams can lead to rapid rises on area streams and rivers. Farther south, this danger has essentially passed.

Agricultural Impacts

In addition to the threat on individual communities, some unprotected agricultural areas will be under water for weeks.

The flooding is occurring much earlier that what typically occurs. The flooding cycle or cycles could run their course, perhaps allowing the ground to dry out in time for the corn and wheat planting season.