Flooding Risk from 2011 Thaw Outlined

February 18, 2011; 5:29 AM ET
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The risk of major flooding across the nation remains rather low into early next week, but there will be some minor problems and ice jam concerns.

Most rivers across the nation were below flood stage as of Thursday morning, February 17, 2011, but an increasing number of rivers were rising, compared to the start of the week. A few were expected to climb above flood stage into the weekend.

Runoff from melting snow was working into some stream and rivers over the Plains and Midwest and was leading to rising water levels. The runoff and the problems it creates will spread into parts of the Northeast over the next couple of weeks.

A flood warning was issued by the National Weather Service for the Illinois River in La Salle and Bureau counties Thursday. The river was forecast to peak just above flood stage, leading to lowland flooding.


There are some years with little or no late-winter and spring flooding issues and others that bring widespread flooding problems. The unfolding thaw will pose "some risk" to northern areas. This National Oceanic and Atmospheric Administration river gauge map shows a lot of green (no flooding). However, more and more yellow and orange colors were showing up this week. Yellow, orange, red and purple dots progress from rivers gauges reporting levels near flood stage to major flooding.

A portion of the Blackwater River in Missouri had risen to flood stage Wednesday morning and had climbed roughly 15 feet in 48 hours. Part of the Little Wabash River in Illinois was just above flood stage. Minor flooding was occurring along the Petite Saline Creek in Missouri.

Officials in Fargo, N.D., were not taking any chances after two years in a row of major flooding and major flooding in four of the last six years. Filled sandbags were being stockpiled and stored in recent weeks for potential use at a later date this winter or spring.


More than 20 inmates from the Cass County jail help at the sandbag filling machine on the first day of sandbagging operations Monday, Feb. 14, 2011, in Fargo, N.D. With a third straight major flood predicted along the Red River in Fargo and neighboring Moorhead, Minn., the voluntary preparations at a city warehouse dubbed Sandbag Central are starting early this year. (AP Photo/Dave Kolpack)

The Red River of the north flows from south to north, similar to many rivers in northern Canada and Russia. This action often leads to springtime flooding in that the headwaters thaw out first and empty into frozen areas below.

The warm-up that began over the weekend and will come into full bloom into many northern parts of the nation this week will lead to significant melting of the snowcover. In many cases, the snowcover will be totally wiped out by the thaw.

Warm, dry winds and little or no rainfall will help to get rid of much of the snowcover in a way as to minimize runoff and not lead to widespread stream and river flooding.

However, there will be rises on many of the rivers and some small streams will approach bank full over portions of the Midwest and the Northeast in the coming weeks. For the most part this is a normal springtime process, but there will be some trouble spots. (The Passaic River in New Jersey and the Connecticut River in New England are examples of some rivers to keep an eye on in the next few weeks, due to the extent of existing snowcover in their basins.)

Though not expected to be a widespread problem, the risk of isolated ice jams will increase over the Midwest and the Northeast this week.

As stream and river levels rise over frozen portions of the waterways, the ice breaks up and flows downstream. The chunks of ice may then clog up downstream, perhaps creating a natural dam. The clog or ice jam then forces water to rise up stream and spill into low lying areas along the river.

It appears it will stay cold enough over the northern Plains, the Upper Midwest and northern New England with a lack of big rainstorms to minimize this concern greatly in the short term.

However, you can still get an ice jam during a thaw without heavy rain.

The area approaching a marginal moderate risk of flooding stretches form parts of the central Plains to the Ohio Valley states, parts of the mid-Atlantic and southern New England.

Flood watches have been issued by the National Weather Service for parts of western New York for the potential of ice jam flooding.

Farther south from the southern Plains to the Southeast, the risk of flooding is negligible due to a lack of moisture in recent snow, no snowcover or lack of rain altogether.

Away from streams and rivers, urban flooding problems will continue as the snow melts, while piles of snow and debris lead to blocked storm drains.

Water running off your roof into frozen downspouts or onto frozen ground can lead to basement flooding.

As we stated earlier on AccuWeather.com, beware as those puddles on some roads may be quite deep containing potholes!

In rural areas, standing water will lay in some fields for a time.

Where the water flows across the road by day and subsides at night, ice can form on these untreated areas.

Otherwise, flooding aside, the next couple of weeks are going to be a rather sloppy period in the history of the winter of 2010-2011.

Just remember, even though while we seem to be breaking the back of winter and much of the nation will have their share of warmth in the coming weeks, the pattern can easily flip for a couple of days. There have been some surprise heavy snowstorms into the first part of April.

The areas that are most likely to get more episodes of snow over the next seven days or so stretch from the northern Plains and northern Great Lakes to northern New England. However, putting shovels away in areas farther south is not recommended.

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