By Doug Schmitz
AMES, Iowa – The current La Niña will affect long-term weather forecasts in 2021, with present soil moisture and snow conditions in the Midwest and the Appalachians also having a heavy effect on future forecasts, according to agricultural meteorologists.
“This La Niña is moderately strong,” Dennis Todey, director of the USDA Midwest Climate Hub in Ames, Iowa, told Farm World. “Therefore, the National Oceanic and Atmospheric Administration’s Climate Prediction Center (NOAA-CPC) outlooks have followed along pretty closely with standard La Niña composites.
“This means generally warmer weather is more likely across the Southern U.S., and a slight chance of colder-than-average in the Northern Plains,” he added. “This year, that possibility of warmth was expanded up to the eastern Great Lakes, and further northeast.”
As for precipitation, Todey said it will be drier more likely again across the far southern U.S., and up into the central Plains.
“Wetter more likely – especially in the Ohio Valley,” he said. “Lower chances of wetter-than-average for the Great Lakes, and far Northern Plains.”
According to NOAA, La Niña is characterized by unusually cold ocean temperatures in the Equatorial Pacific, compared to El Niño, which is characterized by unusually warm ocean temperatures in the Equatorial Pacific.
La Niña strengthened last October, with both the tropical Pacific Ocean, and the atmosphere clearly reflecting La Niña conditions. Forecasters estimate at least a 95 percent chance La Niña will last through the winter, with a 65 percent chance of it hanging on through the spring.
But so far this winter, Todey said, the typical La Niña has not played out just yet.
“Nearly everyone has been warmer than average,” he said. “Precipitation has been somewhat mixed, with dry conditions in the Plains and central Corn Belt, with some intervening wet areas where a few storms have passed through.”
“We have had some snowfalls across most of the north-central U.S., giving us some snow cover,” he said. “That said, I still expect some colder conditions to occur sometime here.
“Maybe later in January, based on computer models right now,” he added. “The cold doesn’t look long-lived in most of the cases; mostly shots of cold that pass through. We do expect that precipitation should pick up here at some point, and become more active.”
He said, however, models have hinted at this a couple times, but it still has not happened.
“Climatologically, we expect more storms with more precipitation later in the winter around the area,” he said. “The additional precipitation is needed where soils are unfrozen to start putting moisture back in the soil moisture profile.
“Where soils are frozen, we will have to wait until thaw for that to happen,” he said.
Justin Glisan, state climatologist with the Iowa Department of Agriculture and Land Stewardship, told Farm World La Niña is the cold phase of the El Niño-Southern Oscillation (ENSO), and plays a role in the location of the jet stream across the United States in winter.
“Analog years – or years in which La Niña has been present – show a greater range of variability in temperature and precipitation behavior than with the El Niño phase,” he said.
“However, knowing that a specific phase of ENSO is present, the longer-range climate models that produce monthly and seasonal outlooks do provide more robust guidance; the absence of El Niño, or La Niña (known as ENSO-neutral) makes seasonal prediction more difficult,” he said.
In addition, Glisan said, “There are other oscillations of varying time scales that impact seasonal forecastability, including the Madden Julian Oscillation (MJO), and Arctic Oscillation (AO). Long story short, there are many factors that impact seasonal forecasts.”
“In terms of temperature, colder-than-average conditions are usually found from the Dakotas through the Pacific Northwest; higher chances of warmer-than-average temperatures are found across the Mid-Atlantic states,” he said.
As for how La Niña will affect long-range forecasts, particularly in the Midwest and Appalachians, Todey said, “The outlooks will be largely influenced by La Niña until we weaken from La Niña category.”
“That is projected to occur sometime this spring,” he said. “Though, in the last few days, there have been hints in the longer range models that La Niña could last into summer. That would increase our drought risk in Iowa.”
“There is still time for a number of things to change,” he said.
“Overall, the drought risks are higher in the Plains, and less so into the eastern Corn Belt/ Appalachians into the growing season,” he added. “There are actually better chances of being wet in the spring in the eastern Corn Belt areas.”