It is news that we feared we would hear: La Nina is back, and will likely strengthen over the next several months. You may recall La Nina is a cooling of the waters in the Pacific Ocean near the equator. The cooling of those waters has an impact on the position of the jet stream, and therefore impacts global weather patterns. In Oklahoma, La Nina patterns tend to produce milder than average weather, and also drier than average weather. That is exactly what Oklahoma does not need given the severe drought that is ongoing.
The La Nina pattern that was in place through the winter of 2010-2011, gradually faded over the spring. But the latest computer simulations and observations indicate that the waters have begun to cool again. Take a look:
You can see the blue areas in the Pacific Ocean off of the coast of South America representing the cooler than normal water temperatures. An intensification of La Nina would lead to a farther northward position of the jet stream in the United States, yielding wetter weather in the north. See the effects of the previous La Nina on rainfall in the United States:
The green areas indicate where rainfall was above normal over the 10 month period ending in July 2011, while the yellow, brown and pink areas are where rainfall was below average. So southern ares (including Oklahoma) were dry, while many northern areas had normal to above normal rainfall. With the forecast of another La Nina winter, it should come as no surprise that the outlook for Oklahoma is not good. The following maps show the prediction of temperatures and precipitation for the months of December, January, and February, otherwise known as meteorological winter:
The temperature forecast calls for temperatures to likely be above average across much of the south.
The precipitation forecast calls for a chance of below normal precipitation across the south. So the outlook is not promising for Oklahoma to see a major shift in the pattern that would bring relief from the drought that is hurting our state. In fact, it is very possible that we will see a continuation of the dry pattern lasting through the upcoming winter.