WSAV NOW Weather: La Niña develops, what it means for the Southeast winter weather

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SAVANNAH, Ga. (WSAV) — Winter weather this year will be a lot different from the cooler- and wetter-than-normal summer weather we had.

La Niña conditions have officially developed in the Pacific Ocean, according to NOAA (National Oceanic and Atmospheric Administration) and the Climate Prediction Center. This will be the cause of a different weather pattern developing.

The phase of the El Niño Southern Oscillation (ENSO) has profound effects on weather patterns across the world. ENSO is a variation of water surface temperatures and a variation of wind speed and strength over the equatorial Pacific Ocean. There are two phases of ENSO, El Niño which is a warm phase or La Niña which is a cold phase. 

A La Niña pattern develops when there are stronger than normal trade winds over the equatorial Pacific Ocean. The trade winds blow from east to west. When the easterly trade winds are stronger than normal, they push the warm surface water toward Asia. That then leads to the upwelling of colder water from deeper levels in the ocean to the surface. 

Colder water near the equator in the Pacific helps change where the jet stream, a current of fast-moving air that sets up between 5 and 10 miles above the surface that moves west to east. Usually, it is farther north than usual.  

When the jet stream is farther north, this usually leads to drought in the southern portion of the U.S. and heavy rain and flooding in the Pacific Northwest. 

Locally in Georgia and South Carolina, we expect warmer than normal temperatures and less rainfall than normal. La Niña conditions are forecast to last through the winter season. 

While we never like to see drought conditions develop, we have been running above average for rainfall throughout the year. So far at Savannah-Hilton Head International Airport, the rain gauge reported 43.49” of rain. That is a surplus of 2.75” of rain compared to a typical year. 

Areas farther north have an even higher surplus of rain for the year. At Augusta Regional Airport, the rain gauge received 48.24” of rain. That is more than a foot above normal for the year so far. 

All that water must make its way out to the Atlantic Ocean through our local rivers such as the Savannah River, Ogeechee River or the Altamaha River. Many of the local rivers are running higher than and some may even reach near flood stage from recent heavy rainfall that occurred over inland communities. 

The developing La Niña pattern will help the southeast to dry out. However, this pattern is not going to be beneficial in areas like southern California and the desert southwest. Drier than normal conditions will only add to the problems they have been experiencing with a prolonged exceptional drought which has led to numerous large wildfires.  

Unfortunately, the dry pattern for the southwestern U.S. will not break until an El Niño pattern sets up. During El Niño years, the southwestern portion of the county typically has wetter and slightly cooler conditions. 

Since the phase of ENSO can take many months to change, it is likely that we will remain in a drier pattern across the south beyond the winter season. If La Niña becomes prolonged into next spring or summer, drought conditions in the southeast can be expected to develop.  

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