Today ended up being a big day for releasing weather data and forecasts, so let’s take a look at the news:

First of all, the Weather Service issued its final Winter 2007-08 forecast. Because of the strengthening La Nina in the Pacific, the revised forecast slightly extends the boundaries of the wet/dry warm/cold areas it predicted in it’s preliminary October forecast. If conditions go according to the forecast, it’s going to be wetter than normal in the Pacific Northwest and in the Ohio/Tennessee Valleys, and drier than normal for much of the southern half of the country, including virtually all of Georgia. It’s also going to be warmer than normal for most of the country, except the Pacific Northwest, with the heart of the heat in the Plains States.

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Accuweather.com has released its Winter 2007-2008 forecast, and it calls for much warmer temperatures than normal for most of the country. Long range forecaster Joe Bastardi says that the beginning and end of the season will probably be closest to normal, but the period from mid-December through February could be one of the top ten warmest winter periods, with the bulk of the warmth centered over the Tennessee Valley and the Carolinas.

Bastardi also has a warning for the drought starved southeast:

“We will know in the next three to four weeks whether a storm from the tropics might arrive to help the southeast drought situation. If that doesn’t materialize, those states are looking at a very dry winter, with precipitation amounts less than half of normal in some areas.”

A combination of La Nina conditions and warming Atlantic Ocean temperatures are the chief culprits for the warm weather. East of a line from the Great Lakes to the Southwest could see temperatures above normal 75% of the time.

Update 10/25/07 - here’s a link to a more detailed winter forecast from Accuweather.

The National Weather Service has issued its predictions for the upcoming winter, and for most of the country, the outlook is for warmer than usual temperatures. The persistent drought in the Southeast is also a concern in the press release put out by NOAA. Here’s a look at the predicted temperatures from December, 2007 through February 2008:

While the greatest chances for above normal temperatures are in the southern Plains states, virtually the entire country with the exception of the Northwest is expected to be warmer than normal. Cooler than normal temperatures aren’t predicted for anywhere in the country. Part of this is due to the long-term trend towards warmer temperatures compared to NOAA’s base years of 1970-2000, and the other part is due to the La Nina conditions expected this winter, particularly in the southeast. Even though temperatures are predicted to be warmer than normal, the Weather Services says that on a nationwide basis, they should be cooler than the 2006-07 winter.

As far as the chance of precipitation goes, much of the southeast and southwest is predicted to be drier than normal, while the northwest is going to be wetter than normal, both due to the La Nina conditions. Also predicted to be wetter than normal is much of the Midwest.

The weather service stressed that this outlook isn’t a snowfall forecast for the season, claiming that it’s difficult to predict exact snowfall patterns more than two weeks out, which is true. I’m a bit surprised that NOAA used the long range outlooks they issued back on September 20th as the basis for their winter outlook, when an updated one is due out in a week, and should in theory be more accurate. Perhaps they wanted to be ‘in the lead’, prior to other forecasters making their predictions.

The Weather Service provided further confirmation to what it had been hinting at for the past several months yesterday, when it issued a news release reporting a developing La Nina condition. The expectation is that La Nina conditions will continue to develop over the next three months, and provide a wintertime La Nina weather pattern. This expectation is backed up not only by observation, but by computer modeling.

If La Nina conditions develop, what can we expect for this winter? According to statistics gathered during previous La Nina years, there is a 49% chance of less than normal precipitation in North Georgia from January through March, and a 60% chance that temperatures will be above normal. There’s only an 8 percent chance of below-normal temperatures, but there is still a 32% chance of above normal precipitation.

La Nina conditions occur when sea surface temperatures in the Pacific Ocean are below normal for more than three months in a row. It is the opposite of El Nino conditions, where equatorial ocean temperatures are above normal. The last time we had a La Nina episode was back in 2000.

A trough in the Eastern part of the United States is going to bring us a real taste of winter weather in the first part of the week leading up to Thanksgiving. There is a reasonable chance of snow flurries overnight Sunday into Monday, but don’t panic — there’s no chance of accumulation. By Tuesday night, temperatures will drop to around 30, or even the upper 20s. You can expect gusty winds throughout the period, so all in all, it’s not going to be a great start to the week.

By Wednesday, the low pressure system will move away from us, allowing warmer temperatures back into North Georgia, with highs possibly brushing 70 degrees by the weekend. The long range prediction is for warmer than normal temperatures through the first of December.

November so far has proven to be colder and wetter than normal. Our rainfall of 3.61 inches measured here is about 170% of normal for the month to date, although if we don’t get more rain it will be about normal for the month. It has been cooler than normal — about two degrees below average so far. So, maybe warm weather for the Thanksgiving weekend will even things out a bit.

Kirk Melhuish of WSB radio has released his winter forecast. It largely follows the pattern of the other major forecasters, with a cooler than normal winter, and normal precipitation. Kirk does think that we’ll have a better chance than normal for an ice storm, though.

The National Weather Service also issued its final update to the winter forecast. While the predicted near normal temperatures and normal to slightly more than normal precipitation is unchanged for the Southeast, the meteorologists have changed their prediction for the Southwest from normal to equal chances of above or below normal temperatures.