Some people – especially cruise-goers – may know the “polar plunge” as taking a dip in the frigid waters (like the Arctic or Antarctic Ocean). But another polar plunge, resulting in air temperatures 30 – 50 degrees lower than normal in some regions, is coming to the US, courtesy of Canada. An Arctic cold front is going to bring dangerously cold conditions across much of the Lower 48, along with snow squalls, sub-zero wind chills, and possible whiteout conditions in a rapidly strengthening “bomb cyclone,” set to significantly impact the Midwest and Great Lakes regions.
The cold is expected to reach as far south as Houston, Texas and parts of Florida. In some states, this will be the coldest December since the late 1980s. In places where wind chills will be far below zero (e.g., Bismarck, North Dakota, is predicted to have wind chills as low as -55 F/-48 C), frostbite could develop on exposed skin in as little as 5 minutes, with hypothermia to follow soon after. Road conditions could get very dangerous as any rain that may be falling ahead of the front “flash freezes” when the Arctic front passes. Pay very close attention to the weather reports in your region – and make sure you’re ready for water breaks and power outages with enough food, water and warm layers (sleeping bags, if you have them).
Canada, where this Arctic blast originates, has been colder than usual since November – and that has been affecting parts of the US, like Colorado, as well. What’s going on? It has to do with what the ocean/atmosphere circulation is doing in the Pacific, off the coast of South America. You may have heard “it’s an El Niño year” in the past. This is the warm phase of the ENSO (El Niño Southern Oscillation), a natural climate variation where trade winds (which typically blow from east to west) slow down, allowing warm water to pile up against the western coast of South America, suppressing cold water upwelling which fishermen rely on for productive fishing. The cold phase of ENSO is called La Niña, when the trade winds blow harder than usual, pushing warm water towards Asia and Australia instead, leaving a large area of cooler equatorial water in the Pacific. The cooler water absorbs/takes heat from the atmosphere, leading to overall cooler global temperatures. However, with recent climate change leading to overall warmer global temperatures, these La Niña conditions don’t have much impact on cooling the planet to any significant scale.
In conclusion, La Niña has been stubbornly persistent this year, leading to the colder-than-average temperatures in Canada as of late. Couple this with a wobbly jet stream and Arctic air can plunge down much further south than it normally would. When there is a large temperature difference between the warmer mid-latitudes and the polar region, the jet stream is strong and keeps cold air up North. But when the difference is smaller, due to the climate changing, the jet stream weakens (it wobbles like how a spinning top wobbles when it starts to slow down) and gets wavier, allowing these types of polar plunges to occur. Stay safe this holiday season!


photo: by Ricardo Peña of Ulyana, Colorado, USA