Generally, La Niña means a warmer, wetter winter than normal. However, Logan Clark, a meteorologist for the Wilmington office of the NWS said this year’s La Niña will be a little different.
What is La Niña?
La Niña is a large-scale weather pattern in which a large area of the surface of the Pacific Ocean around the equator is colder than normal for an extended period, Clark said.
This change causes wide-ranging effects on weather around the world, but for North America the cold water surface tends to push the Pacific jet stream up into the northern Pacific before it turns south through Canada to the Midwest.
That means on average colder conditions for the northern Great Plains and warmer, drier conditions for the southern U.S.
When that area of ocean is warm instead, it is called El Niño. During El Niño periods, there tends to be a strong Pacific jet stream that moves across the southern U.S., producing colder, wetter conditions across the South and milder, less stormy conditions in the North.
What does that mean for southern Ohio?
Most likely it will be warmer and wetter winter than usual across the Ohio Valley.
On average, in December highs in the Dayton/Cincinnati area are in the low 40s, dipping into the upper 30s in January before rising back into the low 40s in February.
However, Clark said this particular La Niña is expected to be weak and shorter-lived compared to other La Niña periods.
Meteorologists expect that with a weak La Niña period there will be less snowfall than normal.
Average total snowfall in southwest Ohio in December is between four and five inches, rising to around eight inches in January and back to between six and seven inches in February.
“There’s always going to be some degree of variability within these large-scale climate modes,” Clark said, adding that there are many smaller factors that affect the weather, and isolated weather events still happen.
For December through February, the Climate Prediction Center’s seasonal forecasts follow La Niña norms.
In a seasonal outlook for those three months issued Nov. 21, the center gave Ohio higher probability of both temperatures and precipitation leaning above normal.
A late La Niña
The timing of a La Niña period also plays a part in how it affects the weather.
This year’s La Niña is developing pretty late in the year, said Emily Becker of the University of Miami in Florida’s Cooperative Institute for Marine and Atmospheric Studies.
In a blog post for the National Oceanic and Atmospheric Administration’s Climate Program, Becker said there have only been two other La Niñas in the last 75 years to develop from October to December.
Because La Niña or El Niño periods reach their peak during the winter, there isn’t much time for this one to strengthen, she wrote.
Overall, she said that this will weaken La Niña’s effects this year on the climate, leaving the door more open to other weather and climate patterns to affect the forecast.
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