March 20, 2008 — -- There is pain today from Texas to Pennsylvania with thousands of people forced to flee floodwaters in more than 250 towns and cities. And the National Weather Service says this week is a taste of things to come.
The government issued its outlook for the next three months today, and predicted an unusual risk of flooding in a broad arc from the Northeast to the mouth of the Mississippi.
"We urge the American people to heed these warnings," said Vickie Nadolski, the deputy director of the weather service, "and not take risks in heavy rain and flood conditions."
The culprits, said forecasters, are continued rain patterns and melting snow from a rough winter in many states.
Floods and droughts are often local phenomena. One county can suffer drought while adjacent counties have had enough rain to relieve the problem. But there has also been a La Nina this winter -- a giant swath of cool water that periodically appears along the equator in the Pacific Ocean and affects the flow of jet streams over it for thousands of miles.
While the La Nina appears to be easing, the forecasters said it has contributed to much of the excessive moisture in the midsection of the United States.
"Above-normal flood potential is evident in much of the Mississippi River basin, the Ohio River basin, the lower Missouri River basin, Pennsylvania, New Jersey, most of New York, all of New England and portions of the West, including Colorado and Idaho," said the weather service, which is part of the National Oceanic and Atmospheric Administration.
Forecasters said Wisconsin and northern Illinois have been unusually wet in late winter, leading to a 20 percent to 30 percent risk of major spring flooding along some rivers.
They also said that snows in parts of New England and upstate New York are a foot deeper than they typically are this time of year, and that snow in the mountains of Colorado and Idaho contain "150 [percent] to 200 percent of average water contained in snowpack."
As the snow melts, water will flow downhill to streams and rivers. But many of those streams and rivers, such as those in mid-Atlantic states, are already inundated.
"All the ingredients are there," said Joanna Dionne, a meteorologist at the weather service. "The soil is like a sponge. But it's already holding most of the water that it can. And then, if it rains, it will run off and cause flooding."
Amid their warnings, the forecasters said there is some good news: The deep drought in the Southeast is gradually easing. It had been severe enough to threaten the water supplies for parts of Tennessee and Georgia, including the city of Atlanta.
High snow in parts of the Rockies should also be a relief to people worried about wildfires in the mountains, said Douglas LeComte of NOAA's Climate Prediction Center.
"That huge snowpack we have in the West," he said, "is good news for the firefighters."