After three months of very hot weather here in Northwest Ohio, your all probably wondering what will happen this fall and winter. Well, I have finally compiled my own forecast for the coming four months, based on ENSO conditions, Pacific Multi-Decadal Oscillation, NAO, and analog past years. Since Accuweather nor NOAA has succeeded with coming up with a seasonal forecast, for this fall or winter, I was forced to do quite a bit of research and insight. As a side note, this is only a preliminary forecast, do not treat this as official or as accurate, because a lot of things may change before this fall/winter season begins. Much of my research was done with the Climate Prediction Center's forecasts for ENSO, NAO, and the Arctic Oscillation. Some of it is based off of trends that have been observed in the last several winters and over the last year and a half.
In the last month and a half, the Climate Prediction Center has issued multiple forecasts on ENSO, and they have finally issued something called a La Nina Watch. In the watch statement, the Climate Prediction Center expects near-neutral to slightly negative ENSO values to continue into late November and early December, which is quite a bit different last year (last year we had rapidly falling temperature anomalies in the Pacific leading to a very strong La Nina). This combined with La Nina like conditions still present over most of the North Hemisphere (abnormally strong jet stream over Canada, enhanced convection over Indonesia, drier than normal conditions over western South America, enhanced hurricane activity over the Atlantic Ocean, etc.), will result in the return of conditions similar to last fall and early winter. According to the La Nina watch, SST (sea surface temperatures) anomalies have been falling gradually in Nina region 3.4 and Nina region 4, which has lead the Climate Prediction Center's forecast to call for weak La Nina to return by December (-0.5 to -1.0 degrees below normal). Computer model ensemble forecasts are pointing to a gradual fall into La Nina conditions by November and December, with some computer models such as the CFS and the NCEP CFSv2 models trending toward moderate La Nina conditions by late December. Also, there is usually a historical tendency for strong La Ninas to be followed by slightly weaker La Nina. With all of this in mind, expect La Nina-like conditions to continue or amplify over the coming months. This means wetter than normal conditions in the Pacific Northwest, a drier Southern US (which is really bad news for the areas in the exceptional drought currently ongoing across a large portion of the Southern US, this will help it become one of the worst droughts ever recorded. For more information on the drought visit
http://droughtmonitor.unl.edu/.), very wet conditions for the Ohio Valley and adjacent Great Lakes, very warm temperatures across most of the Southern U.S., and no climate inclinations over the Northeast (keep in mind that these forecasts are for the months from December through February, and are not in any way forecasts for this fall.) Another major factor in my winter forecast is the North Atlantic Oscillation. This factor determines where and how strong the jet stream will be positioned over the North Atlantic and North America. Generally, during positive periods of the NAO, there is a strong 500 millibar ridge over the central Atlantic, with strong above normal geopotential heights, while over the Iceland there is a strong 500 millibar trough with much below normal geopotential heights. This situation will lead to a strong south-north pressure gradient and a very strong jet stream blowing from North America across the the North Central Atlantic toward Europe. This leads to cool, wet periods during the summer and mild, stormy periods during the winter over Europe. Generally the NAO does not have much of an effect over North American weather patterns during the summer. In the strong negative phase of the NAO, there are generally above normal geopotential heights near Iceland and Greenland (indicating an upper level ridge) and below normal heights and a much weaker pressure gradient between the central Atlantic and Iceland. This type of pattern causes the jet stream to be obstructed well to the north and causes it to move through Greenland and Iceland. During the winter this causes a major trough across the Midwest and Eastern United States, leading to extreme cold and snow. The same thing also happens in Europe. One thing about the NAO is that it can be never be predicted that accurately more than three weeks in advance. But many meteorologists when making a long-range forecast with the NAO, look for trends and patterns that could help predict what the pattern will be like in the next several months. Over the last three years, the NAO has been predominantly negative, which explains the cold winters and giant snowstorms for the East. I'm going to stick with the fact that the NAO will continue to be negative for this winter. Also, the NAO has been predominantly negative this summer. Therefore, I believe that this pattern will continue, leading to me to believe that a trough will dominant the winter pattern ( but not as strong of a trough as last year, as the NAO has been closer to neutral this year).
With these two major factors in play, I believe that this winter will be quite similar to last winter. Mainly because of a developing La Nina, present La Nina-like conditions, the forecast of a predominantly negative NAO, I believe that many parts of the US will not receive a break from frigid and snowy winter weather. Even the places that don't receive extreme weather (such as Texas, Oklahoma, and New Mexico) will still be in exceptional drought, and with a new La Nina developing, drought conditions will get worse. Let's start with the West Coast. Due to La Nina conditions, the much of the West Coast (from Central California on northward) will be very wet again, with below normal temperatures allowing for another great skiing season across the Sierra Nevada and the Cascades. Expect major spring and summer flooding in 2012. In the Rockies and Northern Plains, I would expect another snowy year but with the storm track shifted south of the area and how deep the area of below normal temperatures is expected to be, I would only expect the heaviest snowfall to be during December and March. Temperatures will again be much below normal across the Northern Plains and Rockies. In the Ohio Valley and Great Lakes, the jet stream expected to remain over this area throughout the winter mainly because of a developing ridge in the southeast part of the United States. This region will be extremely wet and snowy throughout the winter with frequent cold outbreaks, but not to the extent of last year's frigid temperatures. Spring flooding will be prevalent again and along with still wet soils could produce another major Mississippi flood in Spring 2012. Over the Northeast and Mid-Atlantic Coastline, I am expecting below normal temperatures for the northern half of the region, while the southern half (south of Pennsylvania) will experience normal temperatures to above normal in extreme southern sections. Precipitation will more than likely be above normal for this region as the jet stream will ride right through the middle of it. Several major Nor-easters could develop again this year, bringing much above normal snowfall to areas from Washington D.C. To Boston, MA. Across the South (from Georgia and Florida to Texas), drier than normal conditions will prevail due to the already dry soils and a ridge that is expected to develop over the southeast. This will cause the exceptional drought to spread to Georgia and Florida, and leading to more wildfires. Temperatures will also be warmer than normal, which will not help the situation at all. Occasionally there could be a significant storm system that could bring northern parts of the south winter precipitation (sleet, freezing rain, snow), but they would be much more likely over Arkansas, Oklahoma, Missouri, and Texas. Finally, in the Southwest, temperatures are expected to border line normal and above normal, mainly because of drier than normal conditions. I expect drier than normal conditions to expand across the Southwest causing a redevelopment of the drought in many areas. Only northern parts of the Southwest (central California, the Sierra Nevada) are expected to receive above normal precipitation.
