Jeff Masters Weather Blog

The weather nightmare before Christmas » Yale Climate Connections

Tens of millions of Americans will find themselves recalibrating – and in some cases canceling – holiday plans over the next week, as an exceptionally intense Arctic front plows across most of the eastern two-thirds of the United States during the run-up to Christmas Day.

Below-freezing air will push to the Gulf Coast by Christmas weekend, with readings likely to dip below zero Fahrenheit from Oklahoma to Ohio late this week. On top of this, a “bomb” cyclone (one that deepens by at least 24 millibars in 24 hours) will race from the Central Plains to the Great Lakes on Friday and Saturday, December 23-24. Fierce winds and heavy snow are expected to produce widespread blizzard conditions and shut down transportation over portions of the Great Lakes and Midwest on one of the year’s busiest travel weekends.

Heavy rains and high winds will buffet the Mid-Atlantic and Northeast before the front arrives, most likely bringing a burst of cold and a quick shot of snow around Saturday (Christmas Eve).

Driving the hellacious winds will be one of the largest surface pressure contrasts ever recorded across the central United States. Computer models insist that an Arctic high-pressure system will peak with a central pressure between 1055 and 1070 millibars in Montana on Thursday or Friday. This high-pressure system will potentially challenge the all-time record for highest surface pressure in the contiguous U.S. of 1064 millibars, recorded at Miles City, Montana on December 24, 1983, during a historic winter onslaught. (For example, that day was Chicago’s single coldest day on record, with a low of -25 degrees Fahrenheit and a high of -11°F.)

Meanwhile, multiple computer models bring the surface pressure at the center of the winter storm down to the 972-977 millibar range in Michigan on Friday. The all-time lowest surface pressures recorded across Michigan range from about 965 to 972 millibars.

A crippling blizzard is increasingly likely across the Midwest

The details are not yet crystal clear this far in advance, but it appears that a dangerous and history-making blizzard is in the cards for parts of the Midwest and Great Lakes. The heaviest snow and highest winds are likely to stretch along a band roughly 50 to 100 miles northwest of the surface low as it intensifies near the mid-Mississippi Valley and hurtles toward Michigan.

Depending on the exact track and timing of the low, heavy snow could be accompanied by bone-chilling temperatures and winds gusting to 40-60 mph anywhere from eastern Kansas around Thursday to northwest Michigan around Friday, perhaps including the Chicago area (and the world’s fourth busiest airport, O’Hare).

The intense dynamics of the storm suggest high snowfall rates, mammoth drifting, and exceptionally dangerous conditions for anyone not sheltered safely at home or elsewhere.

Near the Great Lakes, intensified lake-effect snow as well as lakeshore flooding will be serious threats, with total snowfall amounts of one to three feet likely along portions of the Lake Michigan and Lake Superior shoreline.

Extreme cold will be a hazard even where snowfall is absent or minimal. Readings could dip below freezing for more than 24 hours as far south as Houston, and below zero Fahrenheit for more than 24 hours from Omaha to Minneapolis. Wind chills will be a particular concern given the unusually dramatic wind potential across much of the Plains and Midwest.

From a forecast discussion issued late Sunday by the National Weather Service office in Chicago: “All indications are that our high temp Christmas Day will be the coldest since the mid 90s and possibly one of the top five coldest on record. Any power outages resulting from the strong winds greatly increase potential danger of the cold spell.”

How the imminent cold wave could make its mark in weather history

Strength: It doesn’t appear likely the cold wave will set very many, if any, all-time record lows (although this could happen at a few isolated locations if there’s deep snow cover on a clear, calm night near the very center of the cold air mass). It may be tough for some cities to achieve even a daily record low, if only because the timing of this blast will coincide almost perfectly with the many eye-popping records established in the 1983 cold wave.

At most spots, this will be the kind of cold experienced once every few years, even in our human-warmed climate. It may be more dangerous than usual, though, because of the unusually high winds and low wind chills expected.

Duration: One big saving grace of this week’s weather set-up is the progressive nature of the front and associated storm, meaning they appear more likely to hustle through rather than to stall and linger. The coldest conditions should plague any one spot for no more than a couple of days. Long-range forecast models suggest that much or most of the contiguous U.S. should jump back to above-average temperatures during the final few days of 2022.

Timing: Not only is the Arctic blast arriving just before Christmas, but it’ll strike earlier than many of the worst cold outbreaks in U.S. history, before folks are fully acclimated to winter. The vast bulk of below-zero weather across the Plains, Midwest, and Ohio Valley occurs in January and February.

As winters have warmed in recent decades, frigid readings prior to New Year’s have become even less common. For example, in St. Louis, Missouri — where lows could dip below zero Fahrenheit on both Friday and Saturday, December 23 and 24 — there have been 77 winters in 150 years of record-keeping (going back to 1873) with at least one sub-zero reading. Just 15 of those winters had a sub-zero reading prior to Christmas Day. In other words, such pre-Christmas cold struck St. Louis about once a decade on average.

However, the most recent instance was more than 30 years ago: December 21-23, 1989, a stretch that produced the city’s all-time December low of -16°F on December 22.

Winter weather and climate change

Every weather event now plays out in an atmosphere affected by the addition of greenhouse gases from human activity (mainly the burning of fossil fuels). This doesn’t necessarily mean that every type of weather event will become more extreme or more frequent as a result of human-caused climate change. Like weather itself, the effects of climate change can be variegated, affecting some regions and some types of dangerous weather more than others.

Overall, winters in most parts of the world are getting warmer. That trend is expected to continue in the coming decades. The summary for policymakers of the Sixth Assessment Report of the IPCC, Working Group I, concluded: “It is virtually certain that hot extremes (including heatwaves) have become more frequent and more intense across most land regions since the 1950s, while cold extremes (including cold waves) have become less frequent and less severe.”

As for snowfall, while many winter storms now have access to more water vapor as a result of warming oceans, potentially increasing snowfall in some situations, such enhanced moisture can also push temperatures at any one spot from a snow-making into a rain-making regime. So although it’s well established that rainfall extremes are increasing in our warming climate, changes in snowfall extremes are less straightforward to assess (especially because snow measurement itself is a challenge, and snowfall totals are sensitive to changes in practice).

One intriguing line of research emerged from a series of surprisingly intense winter storms in the U.S. and Europe, as well as a surprising drop in average winter temperatures over Siberia. A scientific debate has now raged for more than a decade on whether the amplified atmospheric warming and increased sea ice loss found over the Arctic might be leading to more-extreme winter weather events in midlatitudes, even if winters as a whole are trending less fearsome over the long term.

As laid out in a series of papers, the core thesis is that the warming Arctic could be making the polar jet stream — and the stratospheric polar vortex it encircles — more unstable and variable. In turn, this could foster vortex displacement events where the polar vortex splits in two, or stretches, thus pushing frigid surface air unusually far south into the midlatitudes. The splitting and stretching could also be influenced by reverberations as the jet stream interacts with enhanced snowfall and high pressure over Siberia during the autumn months.

Scientists across the spectrum of Arctic-midlatitude research have agreed on some points, but there’s still a major split: Simulations from global climate models (including a recent batch specifically tailored to tackle polar-midlatitude relationships) tend to show a weaker correlation between Arctic warming and midlatitude winter weather than what’s actually been found in observational studies. Moreover, the observational links themselves appear to have weakened since the early 2010s, which implies that natural multi-decadal variations could be in the mix as well.

Whether or not the Arctic-midlatitude winter-weather hypothesis stands the test of time, we can’t ignore the threat of winter extremes, as they can persist in a warming climate. By some measures, the cold wave centered in Texas during February 2021 was not the worst one observed there. Yet it triggered a catastrophic failure of the state’s power grid and led to more than 250 deaths in the costliest inflation-adjusted winter storm in modern records.

Jeff Masters contributed to this post.

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