South May Not See Much Relief from Drought This Winter, Thanks to La Niña

   

Linda Lam 
Published: October 25, 2016

Bad news may be ahead for areas in the South seeing very dry conditions.

The drought has become worse in parts of the Southeast the last few months and the dry conditions have begun to spread into other areas of the South.

A weak La Niña may develop this winter and could exacerbate things.

(MAPS: Precipitation Forecast)

What Would Break the Drought?

A persistent upper-level ridge of high pressure brought portions of the Southeast a dry summer with above-average temperatures and these conditions have prevailed into the fall. The result has been a growing drought, especially in northern Georgia, northern Alabama, southeastern Tennessee and western sections of the Carolinas.

Dry conditions have begun to spread Even in areas that flooded as recently as August.

More than half of Georgia is experiencing drought, with 29.24 percent of the state in extreme drought as of Oct. 18, the second-highest category, according to the U.S. Drought Monitor. This includes Atlanta, which has measured about half the amount of rainfall as it would normally expect from Sept. 1-Oct. 24.

Drought conditions across the South as of October 18, 2016 (data from U.S. Drought Monitor).

Almost the entire state of Alabama is experiencing drought conditions. Birmingham received only 0.68 inches of rain Sept. 1-Oct. 24, compared to the just over 6.5 inches that it normally sees during this time period.

The southern and eastern portions of Tennessee are also experiencing drought, with just over half of the state in drought as of mid-October.

A few locations are also on track to see their driest fall on record including Atlanta, Huntsville, Chattanooga and Asheville, according to the Southeast Regional Climate Center.

Western areas of the Carolinas also continue to suffer in drier than average conditions, while eastern sections of the states saw flooding from Hurricane Matthew in early October.

(MORE: Hurricane Matthew Brings Record River Flooding)

According to the long-term Palmer Drought Severity Index, much of northern Georgia, northern Alabama, eastern Tennessee and the western Carolinas would need 9 to more than 15 inches of rainfall over the next four weeks to return to non-drought conditions.

Areas where it rained this summer are not seeing as dire conditions. It was just in August that tropical moisture brought flooding to portions of Louisiana and Mississippi. However, recent warm and dry conditions, along with gusty winds have allowed drought conditions to develop.

Louisiana has seen dramatic changes over the last several weeks. On Sept. 20 none of the state was in drought or even abnormally dry. However, as of Oct. 18, 94.31 percent of Louisiana is now abnormally dry with 38.08 percent now observing drought conditions.

(MORE: Why the Louisiana Flood Happened)

Mississippi has also seen its drought grow over the last few weeks, with 88.74 percent of the state now experiencing drought. On Sept. 6 only 13.77 percent of Mississippi was in drought.

Dry Winter Outlook

The fact that a weak La Niña is expected to develop is one of the reasons that a drier than average winter is anticipated in the South. The influence of La Niña on weather impacts in the U.S. is strongest in the winter. 

However, even if La Niña conditions develop, "it should be weak and potentially short-lived," according to NOAA. This means that there is less confidence for the outlook this winter than if a moderate to strong La Niña was expected. 

(MAPS: Extended Forecast)

La Niña occurs when the central and eastern tropical Pacific sea surface temperatures become cooler than normal, the opposite of El Niño. It is important to remember that the atmosphere needs to respond to the ocean temperatures for a La Niña or El Niño to develop. These conditions also need to last for several months.

December 2016 - February 2017 precipitation outlook from NOAA.

The jet stream tends to track farther north during a La Niña winter, which pushes low pressure systems north as well. This typically leads to a drier than average winter in the southern U.S., while the northern tier is wetter than average. 

The wetter north and drier south is what is anticipated according to the NOAA winter outlook released Oct. 20, depicted in the above graphic. This is in part due to the weak La Niña that is expected to develop.

(MORE: Winter 2016-17 Outlook)

Drought outlook for Oct. 20 - Jan. 31, 2017 for the South (data from NOAA/Climate Prediction Center).

NOAA also looks at what expected precipitation patterns means as far as whether drought areas will see improvement or if drought conditions will grow.

The above drought outlook from the Climate Prediction Center is based on various precipitation forecasts, climate forecast models, climatology and the potential development of La Niña. The drought outlook shows that through January, drought is expected to persist, as well as expand from the western Carolinas westward into eastern Texas. 

It is also important to keep in mind that many other factors influence the weather in the U.S. over a given season. However, the current outlook does not appear to bring a return of wet weather to the South in the next few months.