Winter Outlook 2024-2025: La Niña dominates the US winter pattern

The big story last winter was the development of a strong El Niño pattern. Now La Niña is back this winter and will be the primary influence on the winter outlook. AEM meteorologists, in partnership with WeatherBug, released their winter outlook on November 18, predicting a big change from last year.

With one of the strongest El Niño events in control last winter, most of the United States experienced above-normal temperatures from December to March. “It was particularly warm over the Midwest, Great Lakes and interior Northeast as the jet stream hovered north of them,” AEM meteorologist Rob Richards said. The 2023-2024 winter season was the warmest on record for the Upper Midwest and contiguous United States

Precipitation also followed a classic El Niño pattern across the United States last winter. AEM Meteorologist Rob Richards says, “most of the West Coast, southern United States and East Coast had above normal rain and snow. However, a small portion of the Tennessee Valley observed below average precipitation.”

The El Niño Southern Oscillation, or ENSO, was the main factor considered for the 2024-2025 Winter Outlook. “While current sea surface temperatures are in a neutral phase, there has been a significant cooling trend in the equatorial Pacific. La Niña is expected to develop into the winter and remain in a weak phase into the spring,” said AEM meteorologist Alyssa Robinette.

The Pacific Decadal Oscillation, or PDO, is often described as a long-lived El Niño-like pattern. The extreme phases from the BOB are also classified by sea surface temperatures being either warm or cool in the interior North Pacific and along the US East Coast. The PDO often accompanies ENSO, and the effects can be amplified when both are in phase. AEM meteorologist Alyssa Robinette added, “a negative phase of the PDO developed earlier this year and should continue through most of 2025.”

These outlooks consider both ENSO and PDO to be in sync this year with a La Niña (or cool phase of ENSO) and a cool phase of PDO. Typically, this will bring higher precipitation and mountain snow for the Northwest and Midwest to the Ohio Valley, while most of the southern United States will typically be drier than normal. Colder-than-normal temperatures are usually found in the north-central United States, with warmth overwhelming the southern plains, deep south, and southeast.

Besides the influence of La Niña and a cool PDO phase, other minor factors played a role in the winter forecast, including a positive quasi-biennial oscillation (QBO), a more active Madden-Julian oscillation (MJO), and solar maximum occurrence.

The QBO is a cycle of high-altitude winds that blow easterly or westerly in a belt around the equator, which can affect the global circulation pattern. “A positive QBO, or a westerly phase, would likely mean a weaker polar vortex and a lower chance of arctic air intrusion,” said AEM meteorologist Alyssa Robinette.

The MJO is a wave of enhanced convection followed by a zone of suppressed equatorward convection that moves eastward from the Indian Ocean into the Pacific Ocean over a 30- to 60-day period. “The MJO is typically more active in weak La Nina years,” said AEM meteorologist John Benedict. “Phases in this active MJO would favor above-normal temperatures across much of the eastern and central United States, and generally above-normal rain and snow for the Great Lakes, Mississippi and Ohio Valleys, and the Pacific Northwest,” he added.

During a solar maximum, the polar vortex tends to be more confined to the higher latitudes. “However, when coupled with a westerly QBO, there is a tendency for increased blocking and periodic stratospheric warming episodes, which can occasionally lead to cold air bursts extending further south, particularly in the second half of winter,” the AEM Meteorologist stated. John Benedict.

All of these factors combined will lead to increased chances of the following:

• Below average temperatures in the northern and central United States: With the jet stream dipping further south, there could be more frequent cold outbreaks for the western Great Lakes, Upper Midwest, northern Plains, northern Rockies and even into the Northwest.

• Unseasonably warm for the east coast and most of the southern tier: The jet stream is not likely to drop far enough to the south or east to allow weather systems to move across the East Coast, Gulf Coast, Southern Plains, and Southwest. Even worse, southerly winds south of the jet stream will pump warm air into these regions.

• Snow weather for Northern Tier: Above average precipitation will be likely here given more frequent weather systems. Combined with below normal temperatures, above average snowfall is preferred for the Northwest, Northern Rockies, Northern Plains, Upper Midwest, and parts of the Northeast. Drought improvement and/or removal will also be likely here.

• Expanding drought for the southern US: With a less active weather pattern, it will likely be drier than normal across the south. Drought tolerance and/or expansion is favored across the southern tier, especially in Texas.

• Severe weather outbreaks in the eastern half of the United States: Severe weather outbreaks will be most favored when temperatures are warmer than normal in the east, with below average temperatures in the west. This will cause the air masses to collide and produce severe weather for the Lower and Middle Mississippi River Valley as well as the Ohio and Tennessee Valleys.

The Climate Prediction Center (CPC) released their winter outlook on October 17. They’re also calling for below-average temperatures from the northwest to north-central US, while unusually warm weather is in store for much of the southern US and the East Coast. They highlight two areas where there is the greatest chance of above normal rain and snowfall, which are over the Northwest and Great Lakes. The CPC also favors the southern United States to have below average precipitation this winter.