Nor’easters Explained

We interrupt your spring-leaning inclinations to bring you this winter weather warning.

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I am writing this in advance of Winter Storm Quade. (And incidentally, will someone else at the Weather Channel start naming these things? Quade is not a name; it’s a German slur meaning “evil man”. Maybe that was the intent? But still…) Quade the Storm may fizzle. Or it may be even worse than currently projected — because weather does that. There are still too many variables even for our really big computers. But there will be more winter storms for the Weather Channel to baptize with questionable appellations this year.

Why? Why, I am so glad you asked… Because now Herself can explain things!

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First to recap.

The time around the Wolf Moon — late January into early February — is the coldest time of year in the North. This is likely to remain true even as we head deeper into climate change. At this point in the solar year, the northern hemisphere has experienced short days for many months. Stored surface heat has dwindled and can’t moderate temperature as effectively as it did in the long nights leading up to the solstice. This moderating effect is why we see a time lag between the length of daylight and the seasonal temperature peaks. It’s colder after the winter solstice; it’s warmer after the summer solstice. It takes a while for heat to build up on the surface in the long days of summer and then a while for it to dissipate again in the short days of winter.

(Incidentally, the annual points of temperature maximum and minimum coincide with early August — Lughnasadh — and early February — Imbolg. I say “coincide” but there are no coincidences. The Celtic calendar has these temperature shifts — dubbed thermstices by these people —built into it. And you thought our ancient ancestors were clueless ninnies afraid that the sun wouldn’t rise.)

Another reason the North will remain cold at this time of the solar year even in the midst of global heating is down to climate change itself. Several factors are woven together. In the North Atlantic region, there has been a sharp increase in cold glacial meltwater from Greenland, paradoxically cooling the ocean and the coast in the warmer summer months. This is coupled with a decrease in tropical ocean currents bringing moderating warm waters north as the North Atlantic Current (also called the Gulf Stream since it is generated in the Gulf of Mexico) shifts south under pressure from those cold glacial meltwaters.

There is also a destabilizing effect from the warming of the Arctic. Remember that while it is warming, it is still colder up there than further south. Any air flow that comes from high latitudes is going to be relatively colder. But now there is less of a temperature gradient between polar regions and adjoining temperate regions. The smaller difference in temperature is softening a formerly hard boundary and is letting more air circulate between the two regions.

The circumpolar air flow, the polar vortex, sends projecting loops of arctic air into the temperate south, pushing the northern jet stream deep into the south and inhibiting any overland air flow from the south. Which all makes for long chains of very cold days — even weeks — in the period around the solstice. These bulges in the polar vortex will only become more common as the polar region warms and that smooth circumpolar air flow breaks down. So for the short term (geologically speaking, long term for humans), it will be cold. January, once the snowiest month, will also very likely be drier than it used to be because the air flowing from the north is not able to take up ocean moisture, and the Atlantic isn’t providing that moisture. So the time around the Wolf Moon won’t be as snowy white as it once was. But it will be cold!

However, after the Wolf Moon, when the North has cooled down as much as it’s going to, Greenland glacier melt is at its minimum. So the cold southward flow from Greenland does not inhibit warm northward flow from the Gulf so much in the late winter and early spring. That warm air and water flows up the East Coast and interacts with the Northern jet stream and any polar vortex air the jet stream might have picked up on its travels over the North American continent. Thus, this is prime time for the weather phenomenon we’ve named the nor’easter. (And the Weather Channel is now dubbing with dubious human sobriquets.)

Now, what is a nor’easter?

A nor’easter is a storm along the East Coast of North America, so called because the winds over the coastal area are often from the northeast due to the storm’s counterclockwise rotation. These storms may occur at any time of year but are most frequent and most violent between September and April. Nor’easters usually develop in the latitudes between Georgia and New Jersey within 100 miles of the East Coast. These storms travel generally northeastward and typically reach maximum intensity near New England (yay…) and the Maritime Provinces of Canada. They are nearly always associated with heavy precipitation — all kinds, often mixed up in a horrifying slurry — as well as gale force winds, rough seas, and coastal flooding.

Nor’easters are a product of winter air and ocean flow along the East Coast of North America. During winter, disruption of the circumpolar air flow sends cold Arctic air southward across the plains of Canada and the United States, where this cold air mass gets picked up by the jet stream and is pushed eastward toward the Atlantic. This cold and dry air current slams into the warm and wet air flow of the North Atlantic Current as it flows northward from the Gulf of Mexico. As you know, warm and wet mixed with cold of any moisture level will generate storms. It’s that difference between warm and wet air over the Atlantic and cold Arctic air flowing off the coast that is the fuel that feeds nor’easters.

The storm’s rotation and the resulting wind flow are simple geometry. Air flow from the northwest is slamming into air flow from the southwest, so about at a right angle. Both flows are fairly strong. Picture a jet of water from a hose gushing into a river. The eddies will swirl in loops running downstream (the river current) and looping back toward the hose. Downstream in this case is the air heading north with the North Atlantic current. The polar vortex flow is the hose. So the storm swirls in counterclockwise eddies that we on land experience as wind from the northeast. Out at sea, on the other side of the storm’s rotating center, the winds are flowing toward the northeast. Just to confuse things, occasionally, the storm center will wander far enough inland that land lubbers experience nor-easters with wind from the southwest (or any other direction). This is a problem of our human-centric naming though, not an inconsistency in the storm type.

All this is to say that February and March are likely to see increasing winter storm activity even as we head deeper into climate change. Bostonians still rightfully shudder at the winter of 2015. (Personal note: we were trying to purchase a house in that weather… Couldn’t even open the back door of the house we did buy until after we’d made an offer.) That sort of extreme winter weather straddling the end of winter and the beginning of spring will likely be a feature (and a bug) as the planet heats up. 

So the next time your annoying uncle scoops up a snowball and claims that snow proves “global warming” is a whiney liberal hoax, you can toss all this right back at him. And tell him it’s not global warming — it’s climate change. Terms matter.

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Reference

The National Weather Service. https://www.weather.gov/safety/winter-noreaster, accessed 6 February 2021 at 11:30am.

The Weather Channel. https://weather.com/storms/winter/news/2021-02-04-east-coast-storm-weekend-february, accessed 6 February 2021 at 1:30pm.

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