Ag Weather Forum

It was a very warm overall fall season in 2025. Some bursts of cold air moved through as they always do, but they were fewer and further between this year. We are changing that quickly here to end November and begin December. The winter cold may be front-loaded, however, with more widespread cold expected through mid-January and less frequent widespread cold for the second half of the season.

LA NINA PEAKING IN DECEMBER

Sea-surface temperatures in the tropical Pacific Ocean have been colder than normal since August, crossing the boundary for La Nina, more than 0.5 degrees Celsius below normal, in October. Global models show that La Nina will peak in December and slowly relent through the rest of winter, perhaps even becoming close to El Nino in the late spring.

Peaking early in the winter season would suggest that the wintertime would be more front-loaded. Widespread colder air will be most likely in December and early January, with frequent clippers and visits from arms of the polar vortex.

Some reprieve would be expected then for the second half of the season. This would first start out in the Southeast as a warm upper-level ridge of high pressure forms as La Nina subsides. The storm track would then shift to a fairly typical La Nina position of being from Texas through the Northeast, supplying enhanced moisture through the Ohio Valley. Cold air may still affect Western Canada and the North-Central U.S. into the spring, however.

COLD AIR DOMINATING EARLY WINTER

The downward trend in Pacific Ocean temperatures was well forecast by global models during the last several months, and they have also showcased a colder-than-normal December pattern going back to at least July. DTN forecasters have agreed, looking at years like 2000 and 2010 as similar years which also featured an early peaking La Nina. Those years had cold Decembers, and so the forecast has shown that for several months now.

As November wore on, it became quite obvious that those long-range models and historical years had some merit. During the week of Thanksgiving, we start that trend. A clipper system moving across the northern tier of the country is bringing both a big band of heavy snow and pushing a cold front across the country. Temperatures that had been significantly above normal the previous few weeks will fall below normal for those east of the Rockies.

An even better setup for cold air is on its way for this coming weekend, Nov. 28-30, which features a pair of strong upper-level troughs, one in the West and one in Canada, as well as an upper-level ridge in Alaska. The troughs will supply the energy to produce storm systems and the ridge will provide the cold, dumping it from Alaska southward into the Canadian trough.

This sets up a very stormy and cold pattern for the first full week of December, including chances for significant lake-effect snow events in the Great Lakes.

Models have this pattern relenting a bit during the second week of December, but pour on more cold air for the second half of the month. Those in the West will be shielded from the cold, and those across the south will see mostly bursts of cold followed by relative warmth.

The same sort of pattern is forecast for January. But this time, we may have some influence from the polar vortex, a characterization of the jet stream that circumnavigates the North Pole. Though the vortex is currently weaker than it normally is for this time of year, and expected to be through mid-December, this will not be an influence in the early December cold pattern. However, it may have some influence down the road in late December or, more likely, January.

Disruptions to the polar vortex can mean significant and long-lasting bursts of arctic air, a common feature during La Nina winters across Canada and the northern U.S.

DTN forecasts this to be a larger feature for more of the U.S., though, and could mean significant cold down to the Gulf of America at times.

Without a persistent storm track, precipitation will likely be variable. But large bursts of arctic air are usually accompanied by big storm systems. Some areas of the country should see some significant precipitation out of this pattern, particularly east of the Rockies.

COLD RELENTS FOR LATE WINTER

With La Nina gradually reducing its influence during the winter, this cold pattern is not forecast to last, especially across the southern tier of the country. By late January and especially February, warmer air is forecast to move into the Southeast, which as mentioned, would push the storm track farther north.

What may be sporadic precipitation patterns early in the winter may be more consistent as storm systems favor a track from Texas through the Northeast.

With the Ohio Valley being in the way, increased precipitation is forecast there that could significantly reduce drought heading into spring. In contrast, the Western U.S. would see fewer storm systems and an overall lack of precipitation that may cause drought to increase as the season wears on, especially along the coast.

These effects take some time to come to fruition, though, and a weaker polar vortex through the second half of winter may cause occasional bursts of arctic air through western Canada and the North-Central U.S. A much more variable end to the winter is expected here.

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

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