SECC Winter Climate Outlook
Date Updated:December 20, 2007
Drought likely to continue in Georgia and Alabama, may worsen in Florida. With much colder than normal ocean waters now in place in the tropical Pacific Ocean, it is nearly certain that La Niña will persist and possibly strengthen during the remainder of the winter and well into the spring season. La Niña conditions usually bring warmer weather to the entire region, with temperatures generally averaging 2 to 4 degrees F higher than normal from November through March.
La Niña also brings drier weather to much of the three states, but the pattern does change as the season transitions from fall into the heart of the winter. In November, the shift in average rainfall due to La Niña is 10% to 20% less than normal over the entire area. As the cold season progresses into the heart of the winter, the dry pattern actually pushes southward and intensifies over the peninsula of Florida and the immediate coasts of Alabama and Georgia, where average La Niña rainfall is 30% to 60% less than normal. Central Alabama, central Georgia, and northern Georgia tend to return to near normal rainfall during this time, while northwest Alabama actually tends to be wetter than normal.
The reason for the rainfall patterns seen in January can be attributed to the predominant jet stream configuration that sets up during a La Niña winter. While the position of the jet stream will fluctuate with the passing of individual low pressure systems, fronts, and air masses, the preferred or average setup of the jet steam is that of high pressure or "ridging" over the Pacific near the U.S. west coast and low pressure or "troughing" over the mid-section of the country. This configuration tends to steer winter storms up the Mississippi Valley and Midwest. Unfortunately, this storm track often leaves the Southeast dry and the cold fronts with a little less punch.
How certain is the forecast? Thus far, the maps above and the discussion have centered around "average" shifts in temperature and precipitation due to La Niña. However, no two La Niña episodes are alike, nor are the climate impacts seen from these events. It is important to consider the range of possibilities that accompanies La Niña episodes rather than counting on climate patterns close to the "average" for La Niña. The figures below represent the range of possible precipitation amounts in January for four selected counties in the region plotted as exceedance curves. Simply put, each bar in the graphs gives the probability of rainfall equaling or exceeding the given amount for both La Niña and Neutral (ocean temperature close to normal) climate phases. The graphs demonstrate how the range of possibilities are nearly the same for the two climate phases in central Alabama and Georgia, but shift dramatically towards drier in south Georgia and Florida.
Will a strong La Niña make a difference in the forecast? The strength and extent of the current La Niña has increased during the fall and it can now be considered a moderate to strong event. Analyses have shown that strong La Niña s tend to bring even more intense dryness to the affected areas, and that the dry conditions actually extend farther north into central and northern Georgia and Alabama during the winter. The transition zone between dry and wet moves from central Georgia and Alabama into the mountainous regions. With this in mind, drier than normal winter conditions are more likely in the drought-plagued areas of north Georgia and Alabama if the Pacific Ocean continues cooling.
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So what are the implications for the Southeast? The warmer temperatures will impact winter crops and fruit production, resulting in less chill accumulation over the course of the winter season. Warmer temperatures will also mean greater evaporation rates. Due to the jet stream configuration described above, severe or damaging freezes are less likely during La Niña than in neutral years. However, the risk of early or late season freezes (like in April of 2007) does not seem to be affected by the Pacific Ocean.
The shift towards drier than normal conditions becomes much more pronounced in Florida and coastal Georgia and Alabama as fall progresses into winter, resulting in much higher confidence in a forecast of dry conditions in these areas. La does not impact central and northern Georgia and Alabama nearly as much, so there is much more uncertainty in the precipitation forecast for these areas and near normal is more likely, unless this La Niña grows into a strong event. Even with near normal rainfall, drought conditions are likely to persist in northern Georgia and Alabama, but some lessening of the severity is possible with the winter rainfall. Keep in mind that winter rainfall is vital to the recharge of surface and groundwater in Georgia and Alabama, where summer evapotranspiration rates are greater than normal rainfall, usually resulting in falling water levels. In Florida and southeast Georgia where drought concerns were eased with recent rainfall, there is a strong possibility for drought to reintensify this winter and spring. Wildfires will also be a concern, where studies show that La Niña normally leads to an active wildfire season in Florida and South Georgia.
For more detailed information on El Niño climate shifts in your particular county, please refer to the Climate Risk Tool at AgroClimate:
Climate Risk ToolLa Niña is now fully developed
More information on El Niño/La NiñaThe surface waters in the central Pacific began to take the classic La Niña pattern in September and October. Since then, the colder waters have continued to spread westward and further intensify. In addition, atmospheric indicators in the region including surface winds, pressure, and cloudiness are all consistent with La Niña conditions. Easterly trade winds over the western and central Pacific have been significantly stronger than normal over the last month and a half, which will continue to drive the upwelling of colder water.
A La Niña watch was issued in September by the Southeast Climate Consortium and the state climatologists of Alabama, Florida and Georgia. A watch meant that conditions were likely for the development of a full-fledged La Niña event. La Niña is commonly thought of as the opposite of El Niño. Under La Niña conditions, sea surface temperatures along the equator in the eastern and central Pacific Ocean are a few degrees colder than normal for a minimum of five months. La Niña typically returns every 2 to 7 years.
The watch was upgraded in October to a declaration that La Niña is here and impacting our climate. The La Niña has continued to grow in strength and extent and can now be considered a moderate to strong event. Because of the current strength and the persistent stronger than normal trade winds, there near certainty that La Niña will persist and impact our climate for the next 3-6 months. Click here for our El Niño Discussion.
Current Conditions
Drought areas hit the hardest remain dry. In spite of a couple of storm systems that brought welcome rainfall to Southern Alabama, Central Georgia, and North Florida, the hardest hit areas of North Alabama and North Georgia continued to see below normal rainfall. Consistent with expected La Niña climate patterns, the vast majority of the three states have seen rainfall deficits from 2 inches up to 6 plus inches in Northern Alabama and Georgia. Winter rainfall is vital for the recharge of surface and groundwater in these states and deficits are likely to create water supply problems come spring and early summer. According to the U.S. Drought Monitor, nearly 50% of the Southeast is now classified as being in extreme or exceptional drought. Exceptional drought corresponds to drought conditions that return on average every 50 or 100 years. By some measures the drought northern Georgia and Alabama is the worst on record.
Click image for larger view
For more information on the ongoing drought conditions, including a statement by the Georgia State Climatologist, see the following links.
- U.S. Drought Monitor
- Georgia Drought Statement
- Southwest Florida Water Restrictions
- South Florida Water Restrictions
For more detailed information on recent weather, please see the resources below: