* Drought covers 51 percent of continental U.S.
* Flood risk in northern Plains, Midwest
* El Nino not expected to be a big influence
By Environment Correspondent Deborah Zabarenko
WASHINGTON, March 21 (Reuters) - Lingering snow and colder-than-normal temperatures in much of the United States will give way to warmer-than-average weather and continued drought in areas that need moisture most, the National Oceanic and Atmospheric Administration said on Thursday its spring outlook.
Fifty-one percent of the continental United States is already in moderate to exceptional drought and that is expected to continue in California, the Southwest, the southern Rocky Mountain states, Texas and Florida, NOAA said.
The Midwest, the northern and central Great Plains, Georgia, the Carolinas and northern Alaska may see some relief from drought during April, May and June.
That could be an improvement over 2012, when two-thirds of the country experienced drought conditions and the vast majority of the United States saw record-high temperatures.
The next three months will also bring significant flood risk to North Dakota and northern Minnesota, with moderate flooding possible in the upper Mississippi River basin, including parts of Wisconsin, Illinois and Missouri, said Laura Furgione of NOAA's National Weather Service.
Minor flooding is possible for the lower Mississippi River basin and in the Southeast, including parts of Arkansas, Alabama, Mississippi and Georgia.
Spring is likely to bring above-normal temperatures to most of the continental United States and northern Alaska, except in the Pacific Northwest, the extreme northern Great Plains and Hawaii, which are expected to be cooler than normal.
"We have been experiencing a very unusually cold pattern with a jet (stream) far south of normal," Ed O'Lenic of NOAA's Climate Prediction Center told a telephone briefing. "As the sun gets higher in the sky, sooner or later that's got to stop."
That usually happens by late April, when temperatures are influenced by soils that are then dry and heat up quickly, O'Lenic said. In addition, temperatures in the northern Pacific can influence land temperatures and right now those ocean temperatures are in a relatively warm pattern.
The El Nino/La Nina pattern of warm or cool water in the equatorial Pacific, which can also have a powerful impact on U.S. weather, "is about as neutral as I've ever seen it," he said. In neutral periods, the influence of El Nino/La Nina on U.S. weather is at its lowest.
Snowpack this winter has been heavy in the northern United States, but that will not necessarily alleviate the drought in the country's mid-section, O'Lenic said. Five or six years of dry conditions are unlikely to be undone by seasonal precipitation.
Even this winter's heavy snowpack may not solve the problem, Furgione said.
Because the ground below the snow is frozen so thoroughly, the warm-up expected in April could make snow-melt run off frozen ground without soaking in, she said. (Editing by Christopher Wilson)