By Alex Sosnowski, Expert Senior Meteorologist
Mar 16, 2012; 11:00 AM ET
A lack of snowcover is the major contributor to low spring river flood risk for much of the nation according to the National Oceanic and Atmospheric Administration (NOAA).
Spring snowmelt is traditionally a major player in spring flood potential for northern river systems, including the Connecticut, Delaware, Ohio, Missouri, Mississippi and Susquehanna rivers as well as the Red River of the North.
Unusual and extensive warmth over much of the nation this winter translated to a lack of snowcover at this critical stage of the season.
Snowcover which lays around for weeks and months during the winter tends to accumulate moisture. This moisture is then released in the spring and is a major catalyst for river flooding, especially when combined with a sudden thaw and/or heavy rain.
The lack of prolonged cold weather has resulted in little or no ice formation. As a result, the risk of ice-jam flooding is also low in most areas.
Stream and river flows over much of the nation are currently near or below normal, which is another strike against spring flooding.
Even in the Upper Midwest and northern Plains, which have been hammered by major flooding in recent years, the risk is below normal.
Excessive Rainfall Always a Wild Card
Heavy rainfall can occur just about anywhere during the spring. It is a time of year when weather systems overall are rather strong and there is typically an increasing supply of moisture from the Atlantic, Pacific and the Gulf of Mexico as these water bodies slowly warm.
There are a few areas in particular to keep an eye on.
The NOAA outlined a couple of locations they are concerned with.
The Ohio and lower Mississippi river basins have received above-normal rainfall in recent weeks. Portions of these areas will likely continue to experience above-normal rainfall into the spring.
Since there is little or no snowmelt feeding these rivers in upstream locations, if there is river flooding in these locations, it should not equal the magnitude of last year.
Isolated areas of flash flooding are always a concern entering into the thunderstorm season during the spring and fall. And, it seems the warmth has brought on an early start to strong and drenching thunderstorms this year.
The ground in portions of Kentucky, Tennessee, Ohio and West Virginia are saturated. Slow-moving, drenching thunderstorms with the potential for flash flooding will continue to affect these areas through this weekend.
While the Northwest has received below-average snow and rain this winter, recent moisture-rich storms combined with the potential for additional storms of the same caliber in the coming weeks can drive up river levels and lead to flash flooding of smaller streams.
The St. Patrick's Day Storm will raise the risk of flash flooding in the West (including Southern California).
Mike Smith, Sr. Vice President and Chief Innovation Executive of AccuWeather Enterprise Solutions, has a concern for portions of the central and southern Plains for the week of March 19-25.
Smith in his blog states that recent bouts of heavy rain in the south-central U.S. and the potential for heavy rain next week in much of the same area could drive flooding problems in the region.
Smith believes the area of concern in the short term extends westward and includes not only the lower Mississippi Valley, but also part of the central and southern Plains to eastern Texas.
The St. Patrick's Day Storm hitting the West this weekend will be a slow-mover over the Central states next week with the risk of severe thunderstorms, tornadoes and flooding.
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