Ag Weather Forum

Below-normal temperatures are forecast for a good portion of the U.S. Corn Belt in April. The DTN forecast has long held that April 2025 could have a "winter hangover" of sorts with an extended period of cold temperatures. Forecasts going back to December 2024 showed this potential as La Nina winds down. Looking back through history, we note several times of coming out of weak La Ninas with colder Aprils, and some of the longer-range models had suggestions this would occur.

As winter wore on, it became increasingly likely that April would feature an extended period of cold air. Forecasts of the stratosphere consistently showed a weakening of the polar vortex, essentially the jet stream that encircles the North Pole, during the month of March. When the vortex either gets pushed off of the North Pole or weakens, it can split into pieces that move both down from the North Pole to North America, Europe, or Asia, but also down through the atmosphere to the surface. Typically, this takes 3-4 weeks, giving potential for April to be a colder month.

At the same time, early March forecasts showed the Madden-Julien Oscillation (MJO), a description of a wave of thunderstorms that moves across the Equator, to be in a favorable position to allow for cold air to build in western Canada and pour into the U.S. during April. When the MJO is situated over Africa and the western Indian Ocean, as has been forecast, past events have shown there is increased potential for cold air in the Central U.S.

Model forecasts were also hinting at larger troughing features, or at least weaker ridges, in the upper levels of the atmosphere centered on the Central U.S. in April, a sign that cold air would likely be dumped into the middle of the country during the month.

When the polar vortex, MJO, and extended model forecasts were combined with history, it made sense that there would be a high probability for a cold event during the month of April. But piece by piece, those forecasts have been falling apart in recent weeks.

The early April forecast has shifted to continue the volatile March one, with several large storm systems moving through the country and very little in the way to stop them from doing so. The first week, and likely second, of the month should feature this sort of activity. Wild swings in temperatures should continue due to all the storms moving through, but should average out higher than normal in most areas.

The stratospheric polar vortex has taken a beating over the course of March. Three separate hits have caused it to weaken significantly, replacing the polar low with a high instead. But the main vortex was shifted into Europe and only a small piece is now forecast to break off and move westward into North America in April. This smaller feature is unlikely to provide much support for cold air, though it still has some potential to do so later in the month.

The MJO has also seen some changes in its forecast. With La Nina waning in the Pacific Ocean, warmer waters have altered the upper-level winds around South America and the Atlantic, causing a disruption to the upper-level pattern. The result is a weaker influence from the MJO than we had previously thought, and a slower rotation around the equator. Instead of being in the colder phases, this presentation would suggest the MJO lingering longer in the warmer phases. Models disagree on this to a certain extent with the European suggesting that the MJO does indeed bring us into the colder phases later in April, while the American GEFS has no such wave occurring at the same time, keeping us in the active and generally warm pattern we have seen during much of March.

Despite some of these challenges, extended forecasts of the GEFS, CFS, and European models all have a cold end to the month of April. Below-normal temperatures flood the eastern half of the country, a little different than the current forecast. And the pattern shifts from a very active front half of the month with widespread above-normal precipitation, to a more muted one with fewer and weaker storm systems for the second half. In other words, models are still hanging on to the early forecast, though they are producing a more contracted event at the end of the month and to a lesser degree than we might have thought earlier.

However, even with the consistent agreement in the longer-range models, there is major bust potential in this forecast. If the polar vortex is not able to provide any significant support for cold air, and the MJO does not rotate eastward into Africa and the western Indian Ocean, then the likelihood for a pattern similar to March should generally continue, keeping us wetter and generally warmer with wild swings between storms.

April is a big month for setting the stage for U.S. spring planting. Southern areas likely were able to get through March with fieldwork and starting of their spring planting, making April the big month in which planting is accomplished. Across the north, April brings the hope of increasing soil temperatures allowing for fieldwork and early planting. When that is delayed, it causes short planting windows as cold soils tend to be more risky for early crop emergence and development.

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

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