NewsMarch 21, 2013

Drought and Floods in NOAA's ‘Mixed Bag’ Spring Outlook

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Daniel Yawitz

By Daniel Yawitz

The West and South will continue to face more drought this spring, while the Midwest is likely to see heavy rains and some serious flooding as the northern snowpack melts, according to a seasonal forecast released by the U.S. government on Thursday.

The Seasonal Outlook, a product of the National Oceanic and Atmospheric Administration (NOAA) provides national forecasts for temperature, precipitation, droughts and flood risks for the months of April, May and June, in order to help the public better prepare for the risk of extreme weather events.

Seasonal Drought Outook, March 21 2013.
Click to enlarge the image. Credit: NOAA

 “The big story for the upcoming spring appears to be the expectation that drought will continue across large parts of the South-Central and Southwestern United States, even expanding into California and Eastern Texas,” said Mike Halpert, acting director of the Climate Prediction Center in a video accompanying the outlook.

“Some of those areas, in particular in the central part of that region, have experienced drought now for over a year, and at this time we just don’t see relief coming during the next three months.”

More than half—51.86 percent—of the continental U.S. is currently under some form of drought, with most of those impacts centered in the West, Southwest, and parts of Georgia and Florida, according to the U.S. Drought Monitor. The seasonal drought outlook calls for those conditions to persist and deteriorate over the western half of the country. However, drought is expected to ease over most of the Southeast, and impacts are likely to be short-lived in Florida, which enters its rainy season in June.

Temperatures are forecast to be above average in most of the country this spring. The South-Central U.S., which has suffered the most from drought, has the greatest probability of experiencing above-average warmth.

While temperatures are unusually cold this time of year for some of the country – caused in part by a blocking pattern over Greenland – that pattern is expected to change rapidly in early April, as spring temperatures begin to take over.

Above-average temperatures are forecast in the Eastern two-thirds of the country, although the areas with the highest probability of above-average warmth are in Texas, Oklahoma, and New Mexico, which is likely to make drought conditions there even worse.

U.S. Spring Flood Risk, March 21 2013.
Click to enlarge the image. Credit: NOAA

A sudden change in temperatures could increase the risk of flooding in the Midwest and far northern High Plains, since it could cause the snowpack to melt to early. Late-season snows have left a thick snow cover over the frozen ground in the northern parts of the country. As temperatures start to climb in early April, that snow will turn into runoff. If it gets too warm too quickly, the snow will melt before it can seep into the frozen ground, and lead to serious flooding.

The areas at greatest risk for floods this season are in the Dakotas and Minnesota, in the Red River and Sioux River basins. Areas of the Upper Mississippi Valley, such as southern Wisconsin and Missouri, as well as the lower Mississippi delta, are also at risk. There is a higher risk for floods this spring than in 2012, but floods are not expected to be as severe as they were in 2011.

Flood risks in the Midwest are also exacerbated by the high probability of increased precipitation in the Great Lakes region.

The Seasonal Outlook makes its forecasts based on a combination of climate models, weather forecasts and current climatological observations, such as snow pack, soil moisture, temperature, pressure systems, and global weather patterns like El Niño, which is exhibiting a neutral signal this year. However, the lack of a strong El Niño signal can make creating a forecast more difficult, so the seasonal forecast is far from a sure thing.

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