The Climate Prediction Center (CPC) has issued a La Niña Watch as we head into the upcoming fall and winter seasons. A La Niña or El Niño watch is issued when their respective conditions are expected to take place within the next 3-6 months.
What Is A La Niña?
A La Niña occurs when the easterly trade winds in the equatorial Pacific are stronger than average near South America. This pushes the warm surface water of the Pacific towards Asia and causes an increase in upwelling near Peru and Ecuador. Upwelling brings the cooler water on the seafloor to the surface.
As a result of the warmer ocean water being pushed west, the stormy weather near the equator shifts to the west, and the eastern Pacific near South America sees drier than normal conditions.
This impacts weather patterns worldwide, including ours right here in Northwest Arkansas and the River Valley.
During the wintertime, the southern United States typically sees drier and warmer than average weather. Meanwhile, the Ohio River Valley region can experience a wetter winter than average. A La Niña pattern typically increases precipitation for parts of the west near the Cascades.
Statistically speaking, a La Niña pattern brings more severe weather to Arkansas. Out of the top 4 tornado years in Arkansas’s history, 3 occurred during a stronger La Niña.
The jet steam’s response to a La Niña can help set up a more favorable zone for dry, warm air to collide with wet, cool air over Arkansas. This could lead to more instability over the area and lead to a more desirable environment for thunderstorm development. An active pattern can also lead to many rounds of stormy weather, due to the favorable track of these low pressure systems.
Keep in mind, this is across the entire Natural State, not just NW Arkansas or the River Valley. Plus, there are many other influences that can contribute to tornado formation.