When snow accumulates early across Siberia in September or October, it dramatically increases the surface albedo, reflecting more sunlight back into space.

The result is rapid cooling of the lower atmosphere, which strengthens a dome of cold, dense air over the Eurasian continent known as the Siberian High. This high-pressure area intensifies the temperature contrast between the frigid north and the still-mild mid-latitudes, sharpening what is know as the baroclinic zone where large-scale atmospheric waves form and propagate.

The movement of energy through the atmosphere impacts the generation of these planetary (also known as Rossby) waves. These are the massive undulations that dominate the jet stream, creating what we call upper-level ridges and troughs. These waves act as a communication system between the troposphere (the lower atmosphere where weather occurs) and the stratosphere above.

As theses waves amplify over Eurasia, they can propagate upward into the stratosphere in late autumn. There, they interact with the stratospheric polar vortex, a vast, fast-spinning region of cold air encircling the Arctic at high altitudes that has been making the news almost every time we get a severe outbreak of cold air. When these upward-moving waves become strong, they deposit momentum and heat into the stratosphere, slowing and displacing the vortex. The result is a weaker, warmer, and often off-center polar vortex.

Polar vortex

A disrupted vortex often leads to higher surface pressures over the polar region and weaker westerly winds at mid-latitudes. This state corresponds to the negative phase of the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) — atmospheric patterns that profoundly shape winter weather across the Northern Hemisphere.

When the AO turns negative, the jet stream becomes wavier and shifts southward. Instead of locking cold air in the Arctic, it allows frigid air masses to plunge southward. In North America, this typically brings colder and often snowier conditions to central and eastern regions, while the west may experience milder and drier weather.

The timing of these events follows a rough sequence: early-season snow in October, wave amplification in November, stratospheric weakening in December, and surface impacts by January or February. Thus, what happens over Siberia in autumn can influence the probability of cold snaps months later across North America.

Just like with El Niño or La Niña this relationship is probabilistic, not deterministic — it can increase the chance of a colder winter, in other words, but does not guarantee it.

Many other climate drivers can either amplify, neutralize, or even override the snow signal. So far this year, Siberian snow cover advanced early but slowed in recent weeks, so exactly how much of a factor it will be is still uncertain.

Despite these uncertainties, the Siberian snow connection offers a fascinating example of how interconnected Earth’s climate system truly is. A few weeks of early snowfall in central Asia can set in motion atmospheric waves that travel across continents and through layers of the atmosphere, influencing winter patterns half a world away.

This is one region why the idea of controlling the weather to any large degree is impossible.

Ocean weather impacts

Next up on our list of factors is an anomalously warm northern Pacific Ocean. The northern Pacific is a key energy reservoir for the atmosphere. When it runs warmer than normal, the ocean releases greater amounts of heat and moisture into the air above it. This excess energy thickens and warms the lower atmosphere, building a dome of high pressure that alters normal circulation patterns.

The first major atmospheric feature to be impacted is the Aleutian Low, a semi-permanent low-pressure system near Alaska. Warmer water tends to weaken or displace this low northward and eastward. That change alone can dramatically shift the path of the Pacific jet stream.

A persistent area of warm water in the northern Pacific often gives rise to a ridge of high pressure over western North America. Meteorologists sometimes call this the “North Pacific ridge” or “Gulf of Alaska block.” The ridge acts like an atmospheric wall: it deflects storms northward toward Alaska and the Arctic, while downstream, across central and eastern North America, the jet stream dips southward into a broad trough.

This ridge-trough pairing sets up one of the most recognizable winter patterns in the hemisphere. Western North America experiences mild, dry conditions, often with reduced mountain snowpack and extended drought periods. Alaska frequently sees exceptionally warm, wet winters with rain replacing snow in coastal areas and slower sea ice growth. While central and eastern North America fall under the influence of repeated Arctic outbreaks as cold air slides southward beneath the trough.

The influence of northern Pacific warmth often leads to western Canada seeing mild winter temperatures and less storm activity which means a drier winter with low snow cover. The eastern half of the Prairies often see periodic shifts between warm and cold periods as the western ridge builds and weakens which in turns allows the trough over the eastern half of North America to build and weaken. The repeated back and forth between warm and cold airmass can lead to plenty of storm systems resulting in higher-than-average snow cover.

As you can see, there’s a lot of variables that can affect a long-range winter forcast, with factors pulling it back-and-forth like a tug-of-war, sending conflicting signals.

The post The distant drivers of Manitoba winter weather appeared first on Manitoba Co-operator.

We even talked about it last winter, which was one of the warmest winters on record. So let us dig back into the archives and revisit just what the polar vortex is and how it can influence our weather.

A polar vortex is a large area of circulation (low pressure) in the upper atmosphere that is centred near both Poles and tends to be the strongest in the winter. As the upper air cools, it contracts and its height above Earth’s surface gets lower. This is what creates the area of low pressure in the upper atmosphere. It forms because in the winter the Poles are not receiving any solar energy.

The counterclockwise flow around this region in the northern hemisphere means that the atmosphere flows from west to east. The stronger the air flowing around the vortex, the more circular the vortex tends to be. If the flow weakens, the shape of the vortex tends to get distorted, and we start to see large ridges and troughs form. Ridges are regions where the vortex has pulled northward allowing warm air to move northwards, while troughs are areas where it sags southwards allowing cold arctic air to push south.

We’ve know about the polar vortex for as long as we’ve had the ability to measure the upper atmosphere. It’s likely that it has always been a part of the world’s overall weather patterns, so it is not a new thing. Even the term polar vortex has been used in the literature since at least the 1930s. This is what gets me going when I hear people talking about this feature as it being a new thing — it’s not.

So, the question is: are the cold temperatures we normally see in the winter always the result of the polar vortex? The answer is yes and no. The polar vortex forms as a function of the cold temperatures that develop over our Poles in the winter. As I pointed out earlier, this is due to little to no solar input during this time of the year. The polar vortex, depending on the strength of the winds flowing around it, can create troughs and ridges that can allow cold air to surge southwards. The polar vortex is not the only feature that can influence troughs and ridges, so we can’t always say that every cold snap is directly connected to the polar vortex, but for this current cold snap it certainly was.

When the winds are strong, the polar vortex tends to stay fairly circular and remains in place generally over the Poles. When the winds weaken, undulations begin to form. These undulations are the ridges and troughs that I talked about earlier. Sometimes the polar vortex doesn’t form ridges and troughs, but simply shifts from its usual position. This is what has happened this year.

In late January, it shifted southward to lie over northeastern Canada. The size of the vortex, or upper low, stretches all the way from far eastern Canada into the eastern Prairies, with the southern edge right around the 45th parallel. The million-dollar question is how long will it stick around? Weather models are showing it breaking down towards the end of the month, so let’s keep our weather fingers crossed.

Since I have a bit more room, I thought I would revisit another perennial winter topic – wind chill.

In the winter we have a measurement called wind chill that considers the water vapour that is in the air, wind speed, and the actual air temperature. The wind chill factor indicates the enhanced rate at which the body will lose heat to the air. Our bodies help to keep us warm in the winter by trapping a thin layer of air near the surface of our skin. When it is windy, this thin layer is taken away and additional heat from our bodies is released to try and recreate this layer. This process repeats itself over and over, the higher the wind speed and the colder it is, the faster it goes.

In addition to this, moisture from our bodies is being evaporated — a process that uses up more heat from our bodies. A formula was developed to calculate the rate of heat lost around 1970 and in 2001 the wind chill formula was revised into what we hear about today.

The one thing that still can’t be built into the formula for calculating wind chill is a person’s physical activity, the sun’s intensity and the protective clothing being worn. All of these things can decrease the cooling effect of those cold winter winds, and this is where the problem seems to arise. Some people are arguing that wind chill values are not very good due to these variables. While you could take this argument, I do believe that wind chill values have a place in helping to determine just how cold it feels outside.

What I have an issue with is in how the media uses and reports wind chill. They tend to apply wind chill to inanimate objects like a vehicle. It just doesn’t work that way. Objects can only get as cold as the air temperature. If the wind chill indicates that it feels like it is -45 C but the air temperature is -25 C, then the coldest an object (including a person) can get is -25 C. What the -45 C means is you will be losing heat from exposed areas at a rate equivalent to an air temperature that is -45 C, but once you hit -25 C the object cannot get any colder. So, your car might cool off quicker, but it won’t drop below the air temperature.

If we look at the effect of cold temperatures on the human body, one of the first things our bodies do is contraction, which pulls blood away from the extremities of our body, conserving it to help keep our core warm. This leads to a greater risk of frostbite due to a lack of blood supply, and an increase in urine output. As we continue to cool you can develop hypothermia as you core temperature drops below 35 C. Early signs are shivering, fatigue, and numbness in extremities. Prolonged cold exposures can lead to a suppression of the immune system which can increase a person’s vulnerability of infections.

Hopefully I don’t have write more about cold weather this winter.

While local areas may feel short of snow, the vast majority of the Prairies has seen above average precipitation so far this winter. Part of the reason for this disconnect is that some of early winter precipitation came as rain, and several warm spells brought melting that greatly reduced and compacted the snow pack.

The post The tale behind a polar vortex appeared first on Manitoba Co-operator.

This cold weather got me thinking about different cold weather topics and I found we have not looked at a couple of them in at least four years. The first is one of the most misunderstood weather measurements: wind chill.

When we talk about apparent temperature, we consider water vapour, wind speed and actual air temperature. In the winter, we call this measurement wind chill.

If we look at the effect of cold temperatures on the human body, one of the first things our bodies do is contract. This pulls blood away from the extremities, conserving it to help keep our core temperature warm.

This leads to a couple of things. We run a greater risk of frostbite due to lack of blood supply and we experience an increase in urine output. Now you know why you have to go to the bathroom when you get cold.

These are just the effects of cold on the body, but as almost every Canadian knows, when you add wind, everything changes. In the last cold snap, the -35 C morning had no wind and while it was cold, it did not feel too bad. A day later the temperature had moderated to around -20 C but the wind had increased significantly, and it felt as cold as the -35 C morning, if not colder.

[RELATED] Winter forecasts can be a real mixed bag

The idea of a wind-chill factor was first introduced by Paul Siple in 1939. It indicates the enhanced rate at which the body will lose heat to the air.

Our bodies keep us warm in winter by trapping a thin layer of air near the surface of our skin. When it is windy, this thin layer is lost and additional heat from our bodies is released to try and recreate this layer. The process repeats itself. The higher the wind speed and the colder it is, the faster this cycle repeats and the faster we lose heat. In addition, moisture from our bodies is being evaporated, a process that uses up more heat from our bodies.

A wind-chill formula was developed in about 1970 to calculate this rate of heat loss and it was revised into its current form in 2001, which is what we see and hear about today.

A few things can’t be built into the formula for calculating wind chill, including a person’s physical activity, the sun’s intensity and the protective clothing being worn. All can decrease the cooling effect of cold winter winds and this is where the problem seems to arise.

Some people argue that wind chill values are not very good because of these missing variables. While you could accept this argument, I believe wind chill values can help us determine how cold it feels outside.

But I do have an issue with how the media often uses and reports wind chill.

Media don’t seem to understand how wind chill works and they tend to apply wind chill to inanimate objects like a vehicle, or simply state that the wind chill temperature is the actual temperature.

It doesn’t work that way. Objects can only get as cold as the air temperature. If the wind chill indicates that it feels like -45 C but the air temperature is -25 C, then the coldest an object can get is -25 C. This includes people.

The -45 C means that you will lose heat from exposed areas at a rate equivalent to an air temperature that is -45 C, but once you hit -25 C, an object cannot get any colder. So, your car might cool off quicker but it won’t drop below the air temperature.

[RELATED] Why Manitoba doesn’t see huge lake-effect snows

The second cold topic I want to revisit is the polar or Arctic vortex. As in past winters, this weather phenomenon is starting to make news. The last little cold snap, and most cold snaps we experience, usually have their origins in the Arctic vortex.

The whole idea of the Arctic vortex is not new. It has always been a part of the winter weather pattern across the Arctic but it has been making the news cycle more often in the last decade.

A polar vortex is a large area of circulation (low pressure) in the upper atmosphere that is centred near both poles and tends to be the strongest in the winter. The counter-clockwise flow around this region in the Northern Hemisphere means that the atmosphere is flowing from west to east.

The stronger the air flowing around the vortex, the more circular the vortex tends to be and the more stable it is. If the flow weakens, the shape of the vortex is distorted and we see undulations that create large ridges and troughs. In some cases, these troughs and ridges can become elongated enough that the vortex breaks into two separate circulations. This is what often happens when we see long or deep cold snaps.

A second cause of winter cold snaps happens when the Arctic vortex gets pushed out of its position over the pole by strong northward pushes of warm air. If it gets nudged southward into Canada, the cold air comes with it and will stick around until it is allowed to drift back northward.

Sometimes this happens quickly, with cold snaps lasting a week or so, and other times the pattern locks into place and we see a month or more of extremely cold temperatures.

Let’s hope we do not have to worry about Arctic vortexes too often this winter.

The post Understanding wind chill and the polar vortex appeared first on Manitoba Co-operator.

And La Nina, in turn, is expected to produce hard cold snaps over the Prairies, above-normal precipitation over southern British Columbia and relatively mild temperatures with more snow over Ontario and Quebec, according to private forecasting agency AccuWeather.

The U.S. National Weather Service’s Climate Prediction Center on Oct. 14 reported La Nina — a weather phenomenon marked by unusually cold temperatures on the equatorial Pacific Ocean — had emerged over the past month.

“Negative anomalies” have been observed at depth across most of the central and eastern Pacific Ocean over that time, the agency said.

It also puts the chance at 87 per cent that a “moderate-strength” La Nina will continue over the period from December this year through February 2022.

Forecasters’ consensus then calls for a return to ENSO (El Nino-Southern Oscillation)-neutral conditions during the March to May 2022 period, the agency said.

AccuWeather, in a separate release Oct. 14 including the company’s annual winter forecast for Canada, said this La Nina’s effect, particularly over Western Canada, will likely be temperatures falling “even lower than they do during the average winter.”

Noting last winter’s weather was also under the influence of a La Nina, the company said a polar jet stream “amplified” by La Nina conditions can again lead to colder air and more frequent storms.

“The upcoming winter is expected to be fairly stormy from southern British Columbia through the Canadian Rockies with many opportunities for significant rainfall and strong winds along the coast,” AccuWeather meteorologist Brett Anderson said.

“Abundant” snowfall is expected throughout much of B.C.’s Coastal Range through the Rockies in western Alberta, he said in the company’s release.

“Based on what I see, I think this winter will be wetter than the past five winters in southern British Columbia,” he said. “I think this winter will certainly put a dent in the ongoing severe drought across south-central parts of the province. Conditions have already improved across southwestern British Columbia this fall as drought conditions have almost disappeared.”

Further east, he said, the polar vortex could be displaced from its normal area above the North Pole and drop into the Prairie region from time to time. “I believe we may see at least three extreme blasts of bitterly cold air dropping down into the southern Prairies this winter,” with temperatures dropping below -30 C at those points.

“This winter will likely end up colder than the winter of 2018-2019 and the coldest winter since 2013-2014 in the region.”

Cold snaps across the Prairies this winter should also force a secondary storm track well far to the south in the U.S., Anderson said, and drive storms through the U.S. Rockies and southern Plains of the U.S., before swinging northward into Eastern Canada.

“The majority of the snowstorms will track up into Ontario and Quebec,” he said.

Further east, the company said, the storm track skewing north and west, combined with “very high” water temperatures in the northwest Atlantic Ocean, favours a milder winter with average snowfall in Atlantic Canada. — Glacier FarmMedia Network

The post Another La Nina winter predicted appeared first on Manitoba Co-operator.

That was fully evident earlier this month when large swaths of the U.S. were hit hard by cold.

Suddenly U.S. schools and universities were closed and private businesses, including many in agriculture, were calling a temporary halt to operations. Government organizations, many just back at it following the U.S. federal shutdown, were forced to once again close their doors.

It’s one thing when it’s the southern U.S. Midwest, somewhere like Nebraska with an average daily high in January of 1 C, that suddenly gets smacked by -40 C. However, even nearby North Dakota decided to pull the pin and stay home.

Meanwhile, North of 49, it was largely business as usual, with a side order of bemused superiority. The Winnipeg Free Press and staff writer Kevin Rollason nailed the mood of the day, with a story featuring two photos.

The first was taken in Chicago which was enduring a -28 C blast. It depicted an individual bundled up so tightly about all you could determine was that they were human. A photo taken simultaneously in Winnipeg, where it was -34 C, featured a bare-faced gas jockey pumping fuel with a grin.

The headline put it best: “They call it a polar vortex. We call it home.”

Online, the mood wasn’t much different. My social media feeds featured, among other things, a headline from the Chicago Tribune declaring that metropolis to be colder than Mars, followed by the bland inquiry “First time?” There were also more than a few memes that parodied the Bane supervillain’s monologue from the Batman film “The Dark Knight Rises” reminding the Americans they “only adopted the cold.”

However, it’s easy to feel superior from our perch atop the efforts of our ancestors. We’re better able to manage around this sort of cold because we’ve encountered it more often and we’ve designed countless systems around it.

We all have a block heater in our vehicles. Many of us have dedicated winter tires of rubber compounds that maintain flexibility and grip in the most frigid of conditions. Even more personally we all own — or at least know enough that we should own — decent winter weather clothing.

Meantime, due to their citizens’ relative inexperience with temperatures such as these, the U.S. National Weather Service was forced to caution citizens to “avoid taking deep breaths” lest they freeze their delicate lung tissue.

Our American friends are no doubt going to be able to adapt too, should their future contain more of these sorts of icy polar blasts. And it would appear that’s going to be the case.

Despite plenty of comments about ‘whatever happened to global warming?’ amidst the chill — including one tweet from U.S. President Donald Trump entreating global warming to “Please come back fast, we need you!” — climate scientists assure us what the U.S. has just endured is likely actually an expression of that global warming.

It turns out that the polar vortex is, ordinarily, a very good thing for much of the world, when it’s functioning as it usually does. It’s a ‘whirlpool’ of cold winds that begins every winter, keeping the coldest air of the North Pole farther to the north, while maintaining more moderate temperatures to the south.

It’s when it breaks down, probably due to the effects of global warming and sea ice loss, and separated into multiple ‘pieces’ there’s trouble. Those pieces dip far farther south than ordinary, bringing with them much colder weather to areas unused to it and ill equipped to cope.

The future therefore looks like a world with shorter and warmer winters, punctuated with periods of bone-chilling cold. That could have a huge impact and is going to require a lot of planning to mitigate.

For example, one wonders just how well the often-praised U.S. interstate highway system will fare if it’s suddenly exposed every year to the same pothole-inducing freeze-thaw cycle as Manitoba roads.

Then there’s the simple fact that few things are actually designed for these sorts of conditions. During our recent cold snap, most equipment was clearly at the very limits of its operating ability.

On the agriculture front, it’s questionable just how some crops, like the Midwest winter wheat crop, for example, might fare if suddenly winter includes a shot of -30 C weather once or twice a season.

All told, it’s going to be a big challenge for our neighbours to the south, and no picnic for us either, if it’s going to be a more regular and prolonged occurrence.

It brings to mind the wise words of a local machinery dealer back home when Dad and I once showed up looking for parts.

“Y’know, I’d have less business if you guys stayed home in weather like this with your feet by the fire.”

The post Editorial: Weathering winter appeared first on Manitoba Co-operator.

When we talk about apparent temperature we are taking into account the water vapour that is in the air, wind speed, and the actual air temperature. In the winter we call this measurement wind chill. If we look at the effect of cold temperatures on the human body, one of the first things our bodies do is contract. This pulls blood away from the extremities of our body, conserving it to help keep our core temperature warm. This leads to a couple of things: first, we run a greater risk of frostbite due to a lack of blood supply, and second, we experience an increase in urine output (now you know why you have to go to the bathroom when you get cold).

These are just the effects of cold on the body, but as almost every Canadian knows, as you add in the wind when it’s cold, everything changes. The explorer Paul Siple first introduced the idea of a wind chill factor in 1939. The wind chill factor indicates the enhanced rate at which the body will lose heat to the air. Our bodies help to keep us warm in the winter by trapping a thin layer of air near the surface of our skin. When it is windy, this thin layer is taken away and additional heat from our bodies is released to try and recreate this layer. This process repeats itself over and over; the higher the wind speed and the colder it is, the faster it goes. In addition to this, moisture from our bodies is being evaporated — a process that uses up more heat from our bodies. A formula was developed to calculate the rate of heat lost around 1970 and in 2001 the wind chill formula was revised into what we see and hear about today.

Factors that still can’t be built into the formula for calculating wind chill include a person’s physical activity, the sun’s intensity and the protective clothing being worn. All of these things can decrease the cooling effect of those cold winter winds and this is where the problem seems to arise. Some people are arguing that wind chill values are not very good due to these variables. While you could take this argument, I do believe that wind chill values have a place in helping to determine just how cold it feels outside. What I have an issue with is in how the media uses and reports wind chill.

The biggest problem is that they often don’t really understand how wind chill works and they tend to apply wind chill to inanimate objects like your vehicle. It just doesn’t work that way. Objects can only get as cold as the air temperature. If the wind chill indicates that it feels like -45 C but the air temperature is -25 C, then the coldest an object can get is -25 C; this includes people. What the -45 C means is that you will be losing heat from exposed areas at a rate equivalent to an air temperature that is -45 C, but once you hit -25 C the object cannot get any colder. So, your car might cool off quicker, but it won’t drop below what the air temperature is.

Split vortices

The second cold topic I want to revisit is the polar or arctic vortex. Just like last winter, and the winter of 2013-14, this weather phenomenon is making its presence felt once again across much of Eastern and Central Canada, along with the north-central and northeastern U.S.

A polar vortex is a large area of circulation (low pressure) in the upper atmosphere that is centred near both poles and tends to be the strongest in the winter. The counterclockwise flow around this region in the Northern Hemisphere means that the atmosphere is flowing from west to east. The stronger the air flowing around the vortex, the more circular the vortex tends to be. If the flow weakens, the shape of the vortex tends to get distorted and we start to see large ridges and troughs form. In some cases, these troughs and ridges can become elongated enough that the vortex breaks into two separate circulations; this is what has happened this year. It happened because of a sudden stratospheric warming event that occurred over the high Arctic in late December, which saw temperatures high above the Arctic spike by more than 50 C. This temperature spike then propagated downward over the first couple of weeks of January and disrupted the vortex, causing it to split.

One of these two vortices has taken up residence over northern Quebec, allowing cold air to have an almost continuous path to drop southward. The unfortunate part of this setup is that Manitoba is almost right in the centre of the cold path. The big question is, just how long will this setup last? The answer: Hard to say. In previous years this type of setup has lasted for up to two months. The current mid- to long-range forecasts call for it to break down in early February, but it will take until late February for the colder-than-average air to either warm up or get scoured out of western North America. So be prepared for more cold temperatures, as winter is not quite done yet!

The post Understanding wind chill and the polar vortex appeared first on Manitoba Co-operator.

This forecast period will begin with a large area of strong arctic high pressure sliding southeastward across Manitoba. This high will bring plenty of sunshine along with fairly light winds, but very cold temperatures. Expect daytime highs on Wednesday to struggle into the mid-minus 20s, with overnight lows in the -34 C range. Once this low moves by on Thursday, we will begin to see a weak push of milder air develop on Thursday. This will help our temperatures to slowly moderate toward more seasonable temperatures by the weekend.

An area of low pressure is forecast to track eastward along the northern edge of this milder air bringing clouds along with the chance of light snow on Saturday. The best chances of measurable snow look to be across central regions. A lot will depend on the exact track of this low and on just how strong an accompanying southern low moving across the central U.S. becomes. Right now it looks like the southern low will become the stronger low, sapping most of the moisture from the northern low.

Another area of arctic high pressure is then forecast to begin dropping southeastward out of the Yukon early next week. Ahead of the high and the main push of cold air, we will see some clouds along with a few flurries late on Monday and into early Tuesday. Temperatures ahead of the arctic front are expected to be fairly nice, with highs over the weekend and into Monday forecast to be in the -6 to -10 C range, with overnight lows around -16 C. Once the front moves through, though, we will be back into the deep-freeze, with forecast highs by Wednesday to be around -20 C and overnight lows back into the -30s C.

Looking a little further ahead, the weather models show temperatures moderating toward the weekend, with near- to slightly below-average temperatures forecast to move in and stick around into early the following week.

Usual temperature range for this period: Highs, -21 to -5 C; lows, -32 to -14 C.

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This forecast period looks like it will be a repeat of last week’s. The arctic vortex is predicted to remain strong and continue to spin in place. This will keep our region under a strong north to northwesterly flow, allowing for new shots of arctic high pressure to slide southward every few days. The first high will build southward on Wednesday followed by reinforcing highs on Friday and Sunday. This will keep temperatures close to the bottom end of the usual temperature range for this time of year. Winds don’t look to be too strong, but any wind at these temperatures will help to create extreme wind chills.

We could see a little light snow late on Sunday or Monday as a weak low quickly drops south behind Sunday’s arctic high. Yet another area of arctic high pressure will drop in to begin next week. This will continue our below-average temperatures. By mid-week, the weather models show a dramatic shift in our weather pattern as the polar vortex breaks down, allowing for Pacific energy to push across the northern Prairies. Confidence in this part of the forecast is low, but should it materialize, we will see Pacific air flood across the Prairies starting Wednesday. This will help to quickly scour out the arctic air, with daytime highs forecasted to push above the freezing mark by Thursday or Friday. With the projected storm track, precipitation looks to remain below average, with any significant snowfall remaining well to our north.

Usual temperature range for this period: Highs, -19 to -3 C; lows, -32 to -12 C.

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Anticipation of a freezing blast began to build this week when weather maps and forecast models showed similarities between next week’s system and one that developed in January 2014.

“Upper-level atmosphere configuration very similar in scale + magnitude as infamous Jan 2014 #PolarVortex popularized by me and @afreedma,” meteorologist Ryan Maue said on Twitter on Tuesday alongside maps comparing the two weather systems.

The southward shift in the polar vortex in 2014 brought the Midwest some of its coldest weather in two decades. Icy conditions snarled travel and thousands of flights were canceled or delayed.

Frigid temperatures combined with gusting winds to create life-threatening wind chills as low as -51 C that killed at least nine people.

The coldest weather next week is expected in the Midwest and Northeast starting around Tuesday, according to forecasts that show temperatures in the single digits in some cities.

“The air mass on the way for the middle of December is likely to be substantially colder when compared to that of this past week and this weekend,” AccuWeather meteorologist Paul Pastelok wrote on Thursday.

Temperatures from the northern and central Plains to wide swaths of the Midwest are likely to drop by between 5 and 20 F compared to temperatures this week, according to AccuWeather.

It is unclear how far south the cold air will be felt, according to Pastelok.

Chicago, the largest city in the Midwest, is bracing for temperatures in the teens next week, according to an AccuWeather forecast, which showed a low of -8 C for Wednesday and Thursday.

Further north in Minnesota, Minneapolis-St. Paul NBC affiliate KARE forecasted temperatures dropping to -12 C on Tuesday of next week, then -13 C on Wednesday.

— Timothy McLaughlin is a Reuters reporter covering the U.S. Midwest from Chicago.

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