FRANKFORT (KT) – The National Weather Service is predicting a warmer than usual and wetter than usual winter for Kentucky, at least during the December to February time period, partially due to the weather phenomenon known as La Niña.
The Climate Prediction Center, or CPC, which is part of the NWS, says La Niña conditions have developed and are expected to continue with an 87% chance of La Niña during December 2021- February 2022, which is considered meteorological winter.
El Niño (Spanish for little boy) and La Niña (Spanish for little girl) are two conditions that develop thousands of miles away in the Pacific Ocean but can still have some effect on weather in the Ohio Valley.
-- El Niño includes above-average sea surface temperatures in the central and eastern tropical Pacific Ocean. Over Indonesia, rainfall tends to become reduced while rainfall increases over the tropical Pacific Ocean. The low-level surface winds, which normally blow from east to west along the equator (“easterlies”), instead weaken or, in some cases, start blowing the other direction (“westerlies”).
-- La Niña occurs when you have below-average sea surface temperatures in the central and eastern tropical Pacific Ocean. Over Indonesia, rainfall tends to increase while rainfall decreases over the central tropical Pacific Ocean. The normal easterly winds along the equator become even stronger.
While the effects of both El Niño and La Niña tend to be small across the Ohio Valley compared to the western United States, moderate and especially strong events do at times affect the region. This is especially true during the mid-winter through spring months, which tend to be warmer and wetter than usual, especially during December and February.
There is still much uncertainty for the upcoming winter season, according to the NWS, as on shorter time scales other less predictable climate patterns can cancel out or amplify the typical influence of La Niña. For example:
• Strong cold outbreaks, like in February 2021, typically last a few weeks and are difficult to predict more than 1 to 2 weeks in advance.
• Snowstorms will likely occur at times this winter. However, the frequency, number, and intensity of these events cannot be predicted on a seasonal timescale.
Looking beyond February, while specifics may vary, in general springtime tornadoes and hailstorms are more frequent during La Niña from the southern Plains through the Ozarks to the lower Ohio Valley. There are no guarantees, however. For example, last winter (2020-21) was a La Niña winter but the Ohio Valley did not have a particularly active severe weather season during spring 2021 in Kentucky.