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Posted at 02:15 PM ET, 03/17/2011

NOAA warns of north central U.S. flood threat


(Source: NOAA.)
NOAA issued its spring outlook today and is warning about the potential for “record flooding” in the North Central U.S. for the third straight year.

Snowpack in parts of the north-central U.S. contains some of highest water content levels observed in 60 years. The water-logged snow along with prospects for above average precipitation as temperatures warm are the primary reasons officials are concerned.

Jack Hayes, director of NOAA’s National Weather Service, cautioned the situation should be taken “very seriously.”

Here are key excepts from NOAA’s release that summarizes its outlook:

Areas of highest flood risk:

...the Red River of the North, which forms the state line between eastern North Dakota and northwest Minnesota, the Milk River in eastern Montana, the James and Big Sioux Rivers in South Dakota, the Minnesota River, the upper Mississippi River basin from Minneapolis southward to St. Louis, and a portion of lower New York, eastern Pennsylvania and northern New Jersey. Many metropolitan areas have a greater than 95 percent chance of major flooding, including Fargo, Grand Forks, St. Paul, Davenport, Rock Island, Sioux Falls and Huron. Devils Lake in North Dakota has an 80 percent chance of reaching two feet above last year’s record of 1452.1 feet.

Possible contributing factors for flooding.

...heavy late summer and fall precipitation, which leaves soils saturated and streams running high before the winter freeze; heavy winter snowfall resulting in deep snowpack; stable below-freezing temperatures throughout the winter delaying snow melt; frozen and/or saturated ground which inhibits infiltration of water into the soil, rapid snowpack melt due to warming springtime temperatures; backwater flooding due to ice jams; and heavy spring rainfall accelerating snow melt and adding to the high volume of water already in river systems.

NOAA’s spring outlook focuses on the flooding potential in the North Central U.S. and Northeast but also summarized information about temperatures and precipitation across the rest of the country:

* Temperature: Odds favor above-average temperatures in much of the southern half of the U.S., and below-average temperatures from the Pacific Northwest to the northern plains.
* Precipitation: Odds favor drier-than-average conditions from South Florida and along the Gulf Coast through Texas and into the Southwest. Wetter-than-average conditions are favored across parts of the northern plains.
* Drought: From the Southwest, across the South and northward to the mid-Atlantic, drought has been spreading and deepening since the winter and is forecast to persist in spring. Wildfires will be an increasing threat, especially when humidity is low and when winds are high.

As we discussed in an earlier post, the contrast between colder than average temperatures over portions of the northern U.S. and warmer than average temperatures over the southern U.S., may enhance the likelihood of severe weather during the spring months in between (especially from Arkansas and Missouri into Tennessee and Kentucky) - though the NOAA outlook does not specifically address severe weather potential.

NOAA’s outlook indicates equal chances for above/below average temperature and precipitation in the D.C. metro region.

By  |  02:15 PM ET, 03/17/2011

Categories:  U.S. Weather

 
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