Last week, NOAA's Climate Prediction Center issued their outlook covering the spring months of March, April and May. As seen in previous months, the forecast favors warmer than normal temperatures over most of the nation, from the East Coast to the Four Corners. Only the Pacific Northwest is highlighted for cooler than average weather. The Pacific Northwest, Ohio and Tennessee Valleys, and the southern Great Lakes have odds favoring wetter than normal weather. The Southwest and Gulf Coast are expected to stay drier than average. This will reinforce and expand the on-going drought in those areas of the nation. A well established La Nina was the driving factor in the forecast for the next few months and the Climate Prediction Center expects conditions to last into the spring.  La Nina occurs when the waters of the Pacific Ocean show a general trend of cooling, the opposite of an El Nino. During La Nina periods, the Jet Stream is not usually active in the Southern U.S. This usually leads to less storms systems and below average precipitation. Cooler than normal weather typically occurs across the northern tier of the country and occasionally wetter periods as well.