The Mother’s Day weekend storm brought late-season weather misery to much of the country over the weekend, and continues to cause trouble in the Northeast US. And, it looks like the rainy weather is likely to continue.

The storm initially caused tornadoes in Oklahoma and Missouri before moving into Georgia early Sunday morning. The Atlanta area was placed under a tornado watch as early as Saturday afternoon and the storms struck overnight, with two EF2 tornadoes striking in Carroll and Douglas counties shortly after 4 AM. It had a 25 mile long path, and caused large scale property damage.

An hour later, a third tornado tore into Clayton county near I-675. Also an EF2, this storm had a 13 mile track into Henry, Rockdale and Newton counties with wind speeds of up to 130 MPH. Further south, yet another EF2 tornado caused considerable damage in the city of Macon when it went through Bibb and Twiggs counties, including destroying two businesses and creating a lot of damage at Macon State College.

The fifth tornado caused one death and three injuries as it moved through Laurens county north of Dublin around 6:30 AM. It destroyed several mobile homes in its seven mile path. It was also an EF2. Another tornado touched down near Vidalia around 7:30 AM, and the Weather Service thinks that more tornadoes may have touched down elsewhere in the state.

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The Climate Prediction Center is issued it’s latest update to its Drought Outlook for November through January. The forecast relies both on the current drought conditions in the southeast, along with the typical weather patterns seen during La Nina winters.

The latest outlook, shown at right, calls for the development of drought conditions along virtually all of the Gulf Coast, and the Atlantic Coast, from the Georgia border south through Florida. This change from the previous forecast is in line with what would be expected in a La Nina winter, which calls for dry conditions in the southeast, and with the end of the 2007 hurricane season on November 30th.

Meanwhile, the forecast calls for some improvement in Tennessee and Kentucky, which typically receive more precipitation during La Nina winters. For the portions of Georgia already in an exceptional drought, well, no changes there.

Last week’s rain did little to improve drought conditions in Georgia, although it did provide some relief to Alabama and the Carolinas:

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Georgia State Climatologist David Stooksbury held a press conference today in Athens to discuss the latest Georgia drought conditions, and to explain what he thinks might occur weather-wise over the winter and spring of 2008. Much of what might happen through the next six months depends on the strength of the developing La Nina, including the chances of being able to refill, at least partially, Lakes Lanier and Allatoona.

There is now general agreement that La Nina conditions are developing in the Pacific. La Nina, and her partner El Nino, are descriptions of the two phases of the warmth of the Pacific Ocean surface temperatures compared to normal. In El Nino conditions, temperatures are warmer, while the reverse is true for La Nina. Most climate observers feel that La Nina conditions strengthened in September.

In a press release accompanying the news conference, Stooksbury said,

“The effects of the La Niña pattern differ with its strength. These differences are critical across north and central Georgia, potentially having major impacts on the current drought and the region’s ability to recover this winter and spring.”

If the La Nina conditions remain weak, then there is actually a greater chance of precipitation across extremely north Georgia, and normal precipitation across the piedmont area. In a moderate to strong La Nina, the chance of more than usual precipitation will be limited to the extreme northwest corner of the state. In either case, it’s likely to be warmer and drier over the southern half of the state. You can see the impacts in the image to the right (click on it for a larger version.)

We had best be hoping for a weak La Nina pattern. In the words of Stooksbury,

“If a moderate La Niña pattern develops, there is a high likelihood that north and west Georgia won’t be able to recover from the drought this winter.

The extreme- to exceptional-drought regions of the state may muddle through the winter and early spring. But without significant recharge of the soil moisture, groundwater, streams and reservoirs, conditions next summer could become catastrophic.”

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 Climate Prediction Center has issued it’s outlook for the month of November, and the updated forecasts show the predicted effects of the intensifying La Nina conditions. La Nina conditions occur when sea surface temperatures cool in the Pacific Ocean. The cooler ocean temperatures alter upper air patterns, and tend to cause warmer and dryer conditions in the Southeast, and wetter conditions in the Northwest.

In the discussion of the updated outlook, the Weather Service says that while earlier forecasts were based on computer models predicting La Nina conditions, this month, actual measurements confirm that a weak to moderate La Nina has started, increasing the confidence in the forecast.

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