- A generally colder than usual winter is expected in the northern states.
- Meanwhile, a warmer-than-average winter is expected for the southern US.
- Several factors are driving the forecast, including La Niña.
Temperatures in an updated winter outlook have turned colder in the nation’s northern plains, but this is in stark contrast to warmer-than-average conditions expected in the south.
Areas from northern New England west to the upper Midwest and Pacific Northwest have a chance of seeing below-average temperatures and atmospherics for the three-month winter period from December through February, according to the Outlook for the three-month winter period from December to February released Friday by The Weather Company, an IBM company G2.
In particular, the northern half of Washington through parts of Montana, North Dakota, Minnesota, and northern Wisconsin are most likely to have temperatures below average.
On the other end of the spectrum, a broad area from the Southeast to the Southern Plains and Southwest is forecast to have the best chance of above-average temperatures overall over the next three months.
Keep in mind that this outlook is a general three-month trend. Therefore, we are likely to see periods that are warmer or colder in respective regions of the country compared to those shown above.
With that in mind, let’s examine the monthly details and track some of the factors driving this forecast.
In December, the outlook trended colder in the Midwest but remained generally the same as before along the East Coast.
Meanwhile, in the Southwest and much of the Rocky Mountains, December is most likely to be warmer than usual. However, the extreme of expected warmth relative to the average has diminished from previous projections in the inner west, from southern Montana to much of Utah, Colorado, Arizona and New Mexico.
The dramatic contrast between a colder-than-average northern layer and warmer-than-average temperatures in the south begins to intensify as we head into the New Year.
Overall, the January forecast trended colder eastward from Washington to parts of Montana, the Dakotas, much of Minnesota, northern Wisconsin and Michigan’s upper peninsula.
The area most favored for above-average temperatures has shrunk but still includes parts of the Southwest in the Southern Plains.
The last full winter month is expected to show the sharpest north-south temperature contrast.
Much of the Southeast might think an early spring start is on the cards as this region favors temperatures well above average.
Meanwhile, places from the Northwest to the Northern Plains will need to keep winter coats handy given the increased likelihood of colder-than-average conditions.
Winter Outlook – Questions and Answers
What drives the forecast?
La Niña – the periodic cooling of the waters of the equatorial Pacific Ocean – is again one of the drivers of the winter outlook this year.
“We continue the remarkable trend toward a third consecutive La Niña winter, a relatively rare event in our recorded history, with the last tripeat occurring between 1998 and 2000,” said Dr. Todd Crawford, Vice President of Meteorology at Atmospheric G2.
The cooling of these waters can have an atmospheric domino effect affecting weather patterns around the world.
In the US, La Niña typically means a colder than average winter in the northern and western parts of the country and a warmer south and east.
But this winter there is a potential curveball in La Niña. The atmospheric response, which ultimately matters for our weather patterns, could be weaker than what is typically expected in a La Niña winter. Therefore, other factors in the atmosphere could override the influence of La Niña and result in a greater number of weather pattern changes over the course of weeks.
In addition to La Niña, there are other pieces of the puzzle to consider in the prediction, which leads us to the next question.
What role do polar vortices and NAO play?
Whether the polar vortex stays strong or weakens sometime during the winter can definitely affect the forecast. However, this part of the forecast cannot be predicted until winter is underway.
During the winter of 2020-21, the polar vortex weakened, and although La Niña was present, a large cold snap contributed to the coldest February of February 19 in the Lower 48. The effects of the cold snap resulted in a multi-billion dollar disaster, with Texas being particularly hard hit.
Crawford said the chance of sudden stratospheric warming (SSW) this winter is less than 50%. This warming of the stratosphere in the Arctic typically creates the domino effect that weakens the polar vortex.
Since a SSW is unlikely, it means the polar vortex will remain stronger this winter, keeping colder air more trapped at northern latitudes like last winter.
The only wild card for this expectation is the NAO or the North Atlantic Oscillation.
There are some indications that the NAO could enter its so-called negative phase at times this winter, allowing colder air to flow to the south and north-east.
That’s because there is blocking high pressure near Greenland when the NAO is in its negative phase, causing cold air to rush in over the eastern states through a southward plunge of the jet stream.
Again, this is a factor that cannot be reliably predicted very far in advance, so we will be monitoring it throughout the winter.
Will Tonga’s massive eruption last January play a role?
While it is true that large volcanic eruptions have had a temporary cooling effect on Earth’s climate in the past, the Tonga eruption did not.
“The eruption (of the volcano) in January is not likely to cool the climate because it was an underwater volcano that ejected water vapor and no particles into the stratosphere; on the contrary, water vapor is a greenhouse gas and could have a warming impact on the climate over the next few years,” Crawford explained.
The bottom line, according to Crawford, is that this eruption is not expected to have a significant impact on the weather this winter.
The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science in our lives. This story does not necessarily represent the position of our parent company, IBM.