Ag Weather Forum

The whiplash effect of going from three straight La Ninas to a very strong El Nino and back to La Nina in the course of the last five years is proving to be an interesting time to be a meteorologist with all sorts of crazy weather. The development of widespread and persistent drought from the La Ninas to the complete turnaround across the Plains and South over this past winter has sure been incredible to witness. And we're not done yet. Sea-surface temperatures in the tropical Pacific Ocean are going from above normal (El Nino) to below normal (La Nina) over the course of the next few months. The last time this occurred was in 2020, not that long ago. You may remember how the summer trended that year and those in the Western Corn Belt and Canadian Prairies will sure remember a persistent upper-level ridge throughout all of June. That generally meant hot and dry conditions as a super-wet 2019 turned into a super-dry 2020. Drought has basically been in place for some of the Plains ever since. Eastern areas of the Corn Belt didn't fare too much better. Weather conditions have been far from ideal and even last year's developing El Nino brought a host of weather challenges to the region. And we can bet the developing La Nina will have its own issues as well.

ENSO FLIPPING BACK TO LA NINA

Besides the sun, sea-surface temperatures in the Pacific Ocean are the largest driver of global weather patterns that meteorologists are aware of. Dubbed the El Nino Southern Oscillation (ENSO), above-normal temperatures that are at least 0.5 degrees Celsius above normal are labeled an El Nino. The opposite, or 0.5 degrees Celsius below normal, is labeled La Nina.

Ocean temperatures in the tropical Pacific Ocean have been under El Nino conditions going back to the summer of 2023 and were quite strong. Peak sea-surface temperatures measured a solid 2.0 degrees Celsius above normal over a three-month period centered on November. A reading that warm has only been accomplished five other times in records dating back to 1950, but there have been some significant changes over the last month.

Sea-surface temperatures in the area have been slowly cooling throughout the winter season. And earlier this month, deep sea ocean currents brought a pocket of cold water east through the ocean and up to the surface. That pocket of cold water is expected to expand over the coming months, quickly eliminating El Nino conditions in the spring. It also appears to build in enough cold water to produce La Nina conditions this summer. Models still have some disagreement on the speed and magnitude of this transition, which will be important, but they all have the same general idea of ENSO-neutral conditions in the spring and La Nina conditions in the summer. And that should not be surprising, as each of the last five strong El Nino events that have reached that 2.0-degree Celsius mark in the fall and winter have seen colder temperatures developing the following summer or fall. In fact, almost all of those resulted in two-straight La Nina winters, so buckle up.

The transition to La Nina will make for a significant change in the weather patterns across the globe, including the U.S. this summer. Historically, ENSO has its largest influence on weather patterns during the winter season in the Northern Hemisphere. Those effects during the summer are often more subtle. However, there are some notable effects to the large-scale weather patterns. The main concern is a developing upper-level ridge this summer.

Ridges are notorious for hot and dry conditions. History suggests an upper-level ridge will be likely over the middle of North America in the summer, but persistence of this ridge and its placement are in question. No two La Ninas are the same and other factors come into play as well, but the risk of this ridge developing will be the concern for the summer.

DROUGHT HAS BEEN REDUCED, BUT NOT ELIMINATED IN CORN BELT

The winter has been mostly kind under El Nino. In addition to record warmth across the north, an active southern storm track has all but eliminated drought from the Southern Plains through the Southeast. Other portions of the Central Plains have seen drought reduced as well. But some pockets are still in there. Also, the Ohio Valley usually is not a favored location for precipitation during El Nino. These areas overachieved with precipitation and drought was actually reduced. Soil moisture is still low, but better than the winter forecast. The real trouble spot is in and around Iowa where a good section of the state is in D3 or extreme drought on the U.S. Drought Monitor. Large areas of Wisconsin and Minnesota as well as eastern Nebraska and Missouri are also dealing with significant drought, who have seen precipitation deficits throughout the winter.

On the whole, soil moisture is low in most of the Corn Belt and adjacent areas in the Northern Plains. A snowpack does not exist anywhere in these regions so there is no source to build moisture outside of springtime precipitation. The Southern Plains through the Southeast are in good shape to start off the spring season but will need to have additional moisture to keep up. With soil moisture low across a wide area of the country, planting is likely to go at a good pace, but early growth remains a concern if the dryness cannot be eliminated.

SPRING WEATHER COULD BE CHAOTIC

Spring is usually a season of great change and this season is shaping up to follow those overall trends. Early March has been very warm with a couple of good systems that have moved through. The end of the month is trending colder, but still active, allowing for additional precipitation chances to move through at a good clip. Drought may see further reduction for areas that are hit, which may include those deep drought areas in and around Iowa, but that is not guaranteed of course.

As El Nino fades in April, its influence will too, which could lead to some wild weather. There are some indications here in mid-March that another cold period will develop in mid-April, surrounded by warm periods again. The active temperature pattern is likely to also lead to an active storm track, but the DTN forecast is calling for near-normal precipitation for the month except in the places that do not necessarily need the rain -- from the Gulf Coast through the Southeast and up the East Coast. The forecast is more mixed in the Plains and Midwest, though the trend is for drier conditions in most of these places as well. May could be similar, though the forecast is wetter for a lot of the country.

In all, the spring forecast is neither concerning nor relieving as the variable nature to the season should lead to some areas seeing improving conditions while others deteriorate. This should still lead to mostly good planting conditions, however, but long-term soil moisture conditions may not be all that great going into the heart of the growing season.

SUMMERTIME HEAT COULD BE DAMAGING

A common feature in summer during a developing La Nina is a semi-permanent upper-level ridge over the middle of North America, as noted above. That typically means hot and dry conditions that favor increasing drought and stress to crops. Indeed, the DTN forecast is for hot conditions across the entire country for each month, June through August. In no way would that mean consistent heat, but that could mean prolonged stretches of hot temperatures. However, even with the ridge and hot temperatures being forecast, DTN is also anticipating a bump in precipitation that favors the central and eastern portions of the country, especially in July and August, the two most important months for weather for U.S. agriculture. Even with the heat, if precipitation comes at the right times and with decent-enough intensity, the heat would not be all that damaging. If the rains do not come at a good pace or intensity, then the overall heat could lead to some issues. With summertime thunderstorms, that is likely to happen in some areas, with drought expanding. That is also impossible to predict where that might occur.

However, there is an elevated risk of more widespread drier conditions in the Western Corn Belt again this year. During the La Nina summers from 2020-2022, dryness and drought were persistent problems. Not all areas are treated the same, and the weather may not turn out to be all that bad. Again, every year is different and every La Nina is different. But the historical trends are for drier conditions in the Western Corn Belt again this year. And with the heat and overall lack of substantial soil moisture early this spring season, it could be a tough year for Western Corn Belt and Plains farmers and ranchers.

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John Baranick can be reached at john.baranick@dtn.com

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