Many of our most memorable fall and winter storms, whether they bring heavy snow, strong winds or a sudden drop in temperature, originate from areas of low pressure that form immediately to the east of the Rocky Mountains.

One of these development zones sits over Alberta, producing what we fondly call an “Alberta clipper,” while another forms farther south over Colorado, responsible for the infamous “Colorado low.”

So, let’s revisit why the lee of the Rockies is such a breeding ground for storm systems and why certain lows grow into major weather makers while others barely organize at all.

We’ve previously discussed how the jet stream, with its sweeping curves and shifting speed, helps shape regions of rising and sinking air. When the jet accelerates, rising motion and low pressure often develop beneath it. When it slows, sinking air and high pressure tend to form. While this plays a supporting role, it doesn’t fully explain why lows so often take shape immediately east of the mountains.

To understand that, meteorologists talk about vorticity, a measure of how much spin an air parcel has. There are several types — absolute, relative and the Earth’s own vorticity — but the fine details can be complicated enough to test anyone’s patience. Instead, we’ll focus on the main ideas needed to understand how lee-side lows develop.

As you move closer to the equator, the Earth’s vorticity decreases. Relative vorticity, meanwhile, refers to the air parcel’s own spin — counterclockwise rotation adds positive vorticity and clockwise rotation adds negative.

The important concept is that absolute vorticity, which combines both the Earth’s vorticity and the parcel’s relative vorticity, stays constant unless something forces it to change. So, if an air parcel moves southward and the Earth’s vorticity drops, the parcel must gain relative vorticity to maintain the balance. If it moves northward, the opposite happens. Increasing vorticity encourages cyclonic (low pressure) development, while decreasing vorticity promotes anticyclonic (high pressure) behaviour.

Upward bound

Now imagine Pacific air flowing eastward toward the Rockies. When it reaches the mountains, it is forced upward. At the same time, the tropopause acts like a rigid ceiling, preventing the air from expanding upward as much as it would like. The result is that the atmospheric column becomes squeezed vertically and must, in turn, spread out horizontally. When the column becomes shallower, its absolute vorticity decreases. Because the Earth’s vorticity hasn’t changed at that moment, the parcel’s relative vorticity also has to decrease. This gives the air an anticyclonic, or southeastward, turn as it flows over the mountains and spills down their eastern slopes.

Once the air begins drifting southeast of the Rockies, however, it is now entering a region of lower Earth vorticity. To compensate, its relative vorticity must increase. This creates a cyclonic bend in the flow, turning the air northeastward. Put together, these shifts form a trough of low pressure stretching along the lee of the mountains — a crucial first step in the development of an Alberta clipper or Colorado low.

The next question is why some of these troughs intensify dramatically while others fade. The Rockies themselves play a major part. These are among the tallest mountains on the continent, and their height forces a dramatic squeeze on the air column. The stronger the squeeze, the more the vorticity must adjust, and the deeper the resulting trough. But a trough alone is not enough to guarantee a storm. If it were, we would be dealing with a constant conveyor belt of major lows sweeping across the Prairies all winter long.

Other factors at play

To develop into a significant system, several additional ingredients must align. Cold arctic air often slides southward along the mountains, while warmer, moister air waits to the south. When the developing low taps into both air masses, a strong temperature gradient forms which is a key source of energy for strengthening storms. The moisture adds even more fuel as it rises and condenses, releasing heat that intensifies the system. When these ingredients line up perfectly, an Alberta clipper can quickly spin up and race eastward, bringing snow, wind, and rapid temperature changes.

Colorado lows, meanwhile, owe much of their punch to their southern position. Like clippers, they draw cold air from the north, but they also have access to warm, moisture-rich air from the Gulf of Mexico. Because the Gulf is one of the most reliable moisture sources for the continent, these systems sometimes tap into deep, sustained humidity. As this warm moist air rises and condenses, it releases a tremendous amount of heat, fueling rapid development. This is why Colorado lows can grow into sprawling, slow-moving storms capable of affecting vast regions at once.

Still, not every setup produces a major event. A storm might have abundant moisture but lack arctic air, limiting snowfall and reducing the system’s strength. A promising low might start strengthening only after it has moved east of us, missing the Prairies entirely. Other times, a lack of cold air shifts the storm track farther west, producing more rain than snow or allowing the system to slide too far south to have much impact.

With so many moving parts like the jet stream position, mountain effects, temperature contrasts, moisture supply and timing, it’s no surprise that forecasting these systems can be challenging.

Whether all the ingredients will come together for a major storm this winter remains an open question, but one thing is certain: the unique geography of the Rockies will continue shaping our storm season, just as it has for generations.

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Normally, I would present the full set of weather data, but due to a change in publishing frequency, we’ll return to a more general summary format.

Warm in Manitoba

October continued the pattern of well above-average temperatures that began in September. Across Alberta, mean monthly readings were about 1.0 C warmer than normal, increasing to roughly 2.0 C above average in Saskatchewan.

Manitoba was the warmest of the three provinces, with mean temperatures running 3.0 C to 4.0 C above normal. Winnipeg recorded the highest mean temperature at 8.7 C which was 3.7 C warmer than average, while Peace River was the coolest location, reporting a mean of 4.1 C, still 1.3 C above normal.

Fall rain builds water reserves

Precipitation told a different story. October was wetter than average across the southeastern and northern Prairies, with southern and eastern Manitoba seeing the greatest totals. These wetter conditions stretched northwestward through north-central Saskatchewan and into northeastern Alberta.

Winnipeg stood out as one of the wettest spots, recording 93.7 mm of precipitation, which was nearly 60 mm above the long-term average. North of Winnipeg, I measured over 135 mm at my own location, which made the month feel more like spring runoff than autumn rainfall, with ditches running full and pumps working overtime.

Further west and south, conditions dried out considerably. Regina reported just 28 mm for the month, while precipitation amounts dropped to near zero across parts of southwestern Saskatchewan and southern Alberta. The sharp contrast in rainfall across the Prairies highlights the uneven moisture patterns that continue to shape soil and field conditions heading into winter.

Winter forecast 2025

OK, now back to our winter weather outlook and the factors that may be controlling our winter weather. The early snowfall in Siberia and its influence on the Arctic Oscillation or North Atlantic Oscillation tends to lead to warmer- and drier-than-average winters across the western Prairies, with eastern regions seeing average to below average temperatures along with average to above average precipitation.

The same holds true for a warmer than average northern Pacific: warm dry west, cool wet east. So, if this was all we had to factor in, then I would say there is a pretty good chance this is what we would see this winter.

But there is a third, and in reality, a fourth player. The third player is La Niña, and while it is forecasted to be fairly weak, La Niña conditions often result in a colder-than-average winter across the Prairies with wetter-than-average conditions over western regions with near- to below-average precipitation over eastern regions. This goes against what the other two are calling for.

The last player is random chance and unexpected variations in global weather patterns. Different combinations of events, that on their own leads to a specific outcome, might combine to gives us something new. This is the difficulty in trying to predict long-term weather. While computer modelling has greatly improved forecasts out to 10 or so days, there has not been a huge change in our accuracy in our forecast’s months in advance.

Now let’s look at the different long- range forecasts or predictions and see what they are calling for this winter. Starting off with the almanacs, the Old Farmers’ Almanac is predicting that the winter will see above to well-above average temperatures along with near to slightly above average precipitation. The Canadian Farmers’ Almanac is calling for near- to below-average temperatures this winter and above-average precipitation.

The CFS model, which I find is one of the more accurate, is calling for near-average temperatures this winter with northern and northwestern regions transitioning into below-average temperatures as we work our way into the heart of winter. This model is calling for near-average precipitation across the eastern Prairies and above-average across the west.

Next up is the Canadian CanSIPS model, which is predicting above-average temperatures to start the winter with temperatures transitioning to near average values as we move into December and January. Their precipitation prediction is for a near average start to the winter right across the Prairies with western regions seeing above average amounts during the second half of winter.

The U.S. NOAA’s prediction, extrapolating northwards, appears to be calling for temperatures to start out around average and then transition to below-average. As for precipitation, they are calling for above-average amounts in the west with near- to above-average amounts in the east.

Last on the list of winter weather prediction is the European ECMWF model which is calling for near-average temperatures right through the winter. This is the first time in a long while that this model has departed from predicting above-average temperatures across our region. Their precipitation forecast is similar to most of the other predictions with western regions expected to see above-average amounts with eastern regions seeing near-average values.

If we look to see if there is any kind of consensus, we see a fairly equal split between above-, near-, and below-average temperatures. Precipitation on the other hand is strongly leaning toward near- and above-average amounts.

If I was to go out on a limb, I am leaning toward highly volatile winter temperature-wise with large fluctuations over the winter which will even out to near-average temperatures. As for precipitation, I have to go with the majority and say above-average precipitation with possibly the southern half of Alberta seeing near-average amounts.

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Nobody knows the answer to that question with any certainty, but there are currently three main factors likely to be the driving force behind the type of weather that’s in our future this winter.

The first is La Niña which is currently in a weak stage and is forecast to last until December or January before becoming neutral. The second possible factor is that the northern Pacific is experiencing well above average temperatures. The final factor is the early season snow cover across Siberia.

It’s going to take a series of articles to cover this ground, so this time we will look at La Niña, what it is and how can it impact our winter weather.

Most of us are more familiar with what the related El Niño event is. It is an unusual warming of the central and eastern parts of the equatorial Pacific Ocean. This warming changes the general circulation of the atmosphere over the Pacific. In particular, the trade winds weaken — and in some extreme cases, reverse direction. This can result in large changes in the location of heat and moisture globally and can give rise to anomalous temperature and precipitation events around the world.

La Niña is the opposite. La Niña means the little girl, and can sometimes be called El Viejo, the anti-El Niño, or simply, a cold event. La Niña occurs when there is an increase in the strength of the normal pattern of trade wind circulation. Under normal conditions, these winds move westward, carrying warm surface water to Indonesia and Australia and allowing cooler water to flow up along the South American coast. When a La Niña event occurs these trade winds are strengthened, which helps to increase the amount of up welling which in turn creates more cooler water along the coast of South and Central America and builds up warmer waters on the western side of the Ocean.

On the western side of the Pacific, the influx of warmer water causes an increase in cloud cover over southeast Asia and results in wetter-than-normal conditions for that region during the Northern Hemisphere winter.

Now, the big question is, what does this have to do with our weather in Western Canada?

Limited impact

These changes in the tropical Pacific are usually accompanied by large changes in the jet stream across the mid-latitudes (our part of the world), that shift the usual location of the jet stream across North America. This shifted jet stream can contribute to large changes in the normal location and strength of storm paths and can result in temperature and precipitation anomalies over North America that can persist for several months. Interestingly, these changes are most strongly felt in the winter.

Similar to last year, the latest La Niña advisory is predicting the current weak La Niña to continue through early 2026 before transitioning to neutral conditions. Since La Niña is expected to be on the weak side, this would likely result in limited impact on our weather. For context, let’s just take a look back and see what has happened during previous La Niña winters.

Sometimes it just easier to show the impacts of different weather events with the use of a map. If you look at the map up at the top of this article, it shows the typical impacts on our weather during a La Niña winter across Canada and the U.S. Typically across our region we see colder-than-average temperatures.

The problem is, that map is for a strong La Niña, and it is looking like we will only see a weak La Niña this winter. If we look back at the last 13 weak La Niñas (including last winter), six of them saw near- to below-average temperatures, six were near- to above-average, and one saw above-average temperatures over the eastern Prairies with below average temperatures over western regions. So, statistically, this does not help us out that much in predicting this winter’s temperature, as it is almost a perfect split between whether a weak La Niña winter will be warmer or colder than average.

What about snowfall? Well, once again, we will use a map to help us visualize it. The snow map you see here shows the difference from average snowfall across Canada and the U.S. during the previous nine weak La Niñas. There was a map showing snowfall data for strong La Niñas, but interestingly, it was nearly identical to this map with only a few minor variations. Looking at the map, you can see that during a weak La Niña winter we will, on average, see above-average snowfall over most of Alberta and parts of extreme southern Saskatchewan along with the north central parts of Saskatchewan. The rest of south central Saskatchewan along with southern and central Manitoba typically sees near- to below-average snowfall.

In the next issue we will look at how the current warmer northern Pacific could make a mess out the typical La Niña weather pattern and will also look into what impacts an early snow pack in Siberia might have on the upcoming winter.

Before I sign off, a few interesting weather-related stories have come out. First, global temperatures in September were the third warmest on record. Secondly, scientists believe that due to warming global oceans, the world coral reefs have reached what is very possibly an irreversible die-off. Lastly, global carbon dioxide levels have now reached heights that we have not seen on Earth for 800,000 years. Levels are currently at 424 ppm. When I first started writing weather articles 20-plus years ago it was around 370 ppm.

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When we talk about apparent temperature, or what it feels like, we take into account water vapour in the air, wind speed and the actual air temperature. In the winter, we call this measurement wind chill.

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

Our bodies help 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 taken away and additional heat from our bodies is released to try and recreate this layer. The higher the wind speed, the faster the warm air is pulled away from our bodies.

In addition to this, moisture from our bodies evaporates, which uses up even more heat. In about 1970, a formula was developed to calculate the rate of heat lost, and in 2001 the wind chill formula was revised into what we see and hear about today.

However, a wind chill calculation can’t account for a person’s physical activity, the sun’s intensity and the protective clothing being worn. All these things can decrease the cooling effect, and this is where the problem seems to arise.

But I mostly have an issue with the way the media uses and reports wind chill. They often don’t understand how wind chill works and tend to apply wind chill to inanimate objects like vehicles. 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 it is -52 C but the air temperature is -30 C, then the coldest an object can get is -30 C, and this includes people.

What the -52 C means is that you will lose heat from exposed areas at a rate equivalent to an air temperature that is -52 C, but once you hit -30 C, you can’t get any colder. So, you or your car might cool off more quickly, but won’t drop below the actual air temperature.

Holiday wish list

Now let’s look at some weather gift ideas. I am a little late for this but maybe you can take advantage of after-Christmas deals. I’ll concentrate on a few weather stations available on Amazon.

Weather stations come in several different varieties. You can start with a basic backyard station that reports temperature, humidity and barometric pressure to a console or display that sits in your house. This type is easily found at Canadian Tire and other retailers.

You can up your game a bit and get a station that also does wind and rainfall. The next step is to get a station that reports all these measurements and is able to connect to the internet, which will allow you to access your data from anywhere.

I am an avid proponent of Davis weather stations, but when my last Davis station wore out, I replaced it with an Ambient station because of cost. I got a very good station for around $700, which included extra sensors like soil moisture and soil temperature. This compares to the equivalent Davis station that now costs well north of $1,500 for the same type of setup.

Not too long after getting that Ambient station, I noticed on Amazon a station under the brand name of Ecowitt that looked like nearly the same thing. This led me to conclude that Ecowitt, or some other parent company, was making the Ambient weather stations.

If you search Amazon for weather stations, you will find many different brands and I have no way of knowing how good or bad they are, but I feel fairly confident in commenting on the Ecowitt stations.

The Ecowitt HP2553 Wi-Fi weather station looks exactly like the one I have from Ambient. It comes with a nice colour indoor display, ultrasonic anemometer (wind speed and direction), self-emptying rain gauge, as well as outdoor and indoor temperature and humidity.

As the name implies, it can connect to wi-fi and upload data to Ecowitt’s hosting site, which will allow you to view your data from anywhere. All this for the price of $399.99 with free shipping if you have Prime. You can also get additional sensors. You can even get a lightning detector for $62.

The Ecowitt HP2551 Wi-Fi weather station has the same features as the previous station, but instead of the ultrasonic anemometer, it uses the good old-fashioned wind cups and wind vane. This station also has a UV detector. Price on this one is $299.99. If you look on Amazon, you will see a few other Ecowitt weather stations with slightly different price points.

One interesting station Ecowitt offers is the Ecowitt Wittboy. It measures all the usual things, plus UV, but for rainfall it uses a haptic rain sensor that works by detecting the vibrations of rain hitting it. They are supposed to be quite accurate, but I have never used one to verify this.

This station does not have an indoor display. Instead, a hub collects data and sends it to the Ecowitt servers, allowing you to access data online from phone or computer. At first this might seem strange, but I admit I rarely look at my display anymore. Cost of this station is $249.99.

If you do get an Ecowitt station, let me know what you think.

The post Understanding wind chill appeared first on Manitoba Co-operator.

Now that is time to write about forest fire smoke, it is no longer an issue, hopefully for good this summer. But we know weather patterns can change on a dime, and a couple weeks of wet weather does not bring the end to a drought or the end of forest fires this season.

Smoke and its effects can vary greatly depending on the state of the atmosphere, amount of smoke, where in the atmosphere it is located and how long it stays over a region. It is also affected by large-scale atmospheric events such as high and low pressure systems. I will do my best to peer through the smoke and bring you a clear picture of its impact on weather.

• RELATED: How is corn impacted by wildfire smoke?

The first major and obvious impact is the effect of smoke on temperatures. Smoke particles both scatter and absorb sunlight, which leads to lower surface temperatures. Daytime temperatures often don’t reach the forecasted high for the day when smoke is present because less sunlight reaches the ground, resulting in less heating.

Weather models have difficulty incorporating the location of smoke. The effect on temperatures varies, depending on the extent, level and intensity and general atmospheric conditions. Light smoke or very high smoke will have minimal effect, while dense or low-level smoke can greatly affect temperatures.

Then there is atmospheric stability and precipitation patterns. I’ve lumped these together, since atmospheric stability is directly tied to whether precipitation can form. Forest fire smoke can have complex effects on atmospheric stability, depending on factors such as the intensity and extent of the smoke, vertical distribution of smoke particles and general atmospheric conditions.

Smoke from forest fires can release significant amounts of heat and moisture into the atmosphere. Solar radiation is absorbed by smoke particles, which can warm the surrounding air. This heating can change the temperature profile of the atmosphere and alter its stability.

In certain cases, forest fire smoke can inhibit convection and limit formation of convective clouds. This may sound counterintuitive, but smoke particles can act as cloud condensation nuclei or ice nuclei, allowing moisturetocondense around these particles at a much higher number than in a smoke-free atmosphere.

This reduces availability of water vapour, making it more difficult for cloud droplets or ice crystals to grow larger. Instead of growing bigger into raindrops, tons of little water droplets are formed but can’t grow large enough to fall. This can also result in suppression of convective activity, and we only see the formation of shallow or thin clouds.

While this scenario is common, it can go the other way too. If there is enough moisture in the air, and issues with atmospheric stability are overcome, all the extra condensation nuclei that create large numbers of water droplets can start a chain reaction. The water droplets collide and combine into larger raindrops within the cloud. This can lead to more intense rainfall and formation of hail.

Smoke from forest fires absorbs sunlight. While this can and often does decrease surface temperatures, it can and often does increase the air temperature at higher altitudes, depending on where the smoke is in the atmosphere. This creates a layer of warm air over a layer of cold air. Since warm air wants to rise and cold air wants to sink, this particular setup is known as a stable atmosphere.

Unstable air, which leads to cloud formation and precipitation, is when we have cold air over top of warm air. The warm air at the surface wants to rise and will continue to rise because the air above is colder. In the case of smoke, the surface temperatures are cooled by the smoke but warmed higher up, as the smoke absorbs energy from the sun. This causes a stable air column or an inversion.

This setup inhibits convection, which is the primary force behind cloud development and precipitation. This is probably one of the biggest impacts smoke can have on our weather.

So, smoke can either inhibit formation of rainfall or enhance it, depending on the atmospheric conditions at the time. More often than not, smoke creates a stable atmosphere, resulting in reduced rainfall because convection is limited.

Another impact of smoke relates to the chemicals released by forest fires, such as nitrogen oxides and volatile organic compounds. These chemicals can interact with other atmospheric components and influence the overall chemistry of the atmosphere, contributing to formation of secondary pollutants such as ozone and particulate matter. This can have an impact on human health but also the health of animals and plants.

I have my fingers crossed that the western Prairies, northern regions and B.C. will continue to get much-needed rain. That will help control forest fires and provide moisture as we head toward the main part of the growing season.

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As any Prairie farmer knows all too well, untimely frosts can result in substantial losses and the length of the frost-free season restricts agricultural opportunities. Dates of the last spring or first fall frosts vary from year to year, but overall, they are relatively constant.

If they were really constant, we wouldn’t have to worry about losing a crop or flowers to a late spring frost. Despite what one might instinctively think, the risk of frost is rising as the planet warms.

In some years we experience an early last spring frost date, even for a few years in a row. We begin to get used to it. Then we get a late final frost, and it hits us all the harder. This is the variability we’ll have to deal with over the next few decades.

There has been considerable study relating to frost and its effects on plant life. It’s an area of personal interest, because I chose that topic for my bachelor’s thesis in the early 1990s.

This week we will explore the relationship between frost, topography and crops.

How is frost defined? Using a climatic definition, frost occurs when the temperature of the land surface drops below 0 C, but with respect to agriculture, frost is substantially more difficult to define.

Looking at cereal crops, for example, a temperature of 0 C will not result in crop death. In fact, the crop will rarely be damaged at that temperature. When it comes to agriculture, the terms killing frost or freeze are more useful.

A killing frost usually refers to conditions in which more than 50 per cent of the vegetation in a region has been killed by frost, and a freeze is when ice crystals form in plant tissue, resulting in permanent injury.

At what temperatures are different crops affected? There are three development stages in which crops have varying degrees of resistance to frost: germination, flowering and fruiting.

The germination stage has the greatest resistance to frost, whereas flowering has the least resistance. In the germination stage, crops such as spring wheat and oats can resist temperatures as low as –8 to –10 C. Compare this to crops such as corn, cucumbers and tomatoes, which will suffer damage when temperatures drop only slightly below 0 C.

In the sensitive flowering stage, every crop is susceptible to frost, with critical temperatures in the 0 to –3 C range, so this period of growth concerns growers the most when dealing with frost.

Topography can have a significant effect on which areas receive frost. Since cold air is denser than warm air, it will flow downward and accumulate in lower areas. This phenomenon has been referred to as frost hollows, cold islands, cold air pooling and cold air lakes.

No matter how you describe it, there doesn’t have to be a huge change in elevation to have a significant impact on temperature. In one study, a change of less than one metre in elevation over 100 metres resulted in overnight temperature differences of 3 C to 5 C. This is why you can experience frost even though your thermometer says it’s above freezing.

I know this from personal experience. You can’t tell by looking at my land, but I am at a low spot — by only about one metre. I can see this in spring when there is heavy runoff. Due to this dip, I routinely get frost or much colder temperatures than my neighbours. I’ve done the science and collected the data.

How can you protect yourself from frost? If you have 500 acres of wheat, there is not much you can do, but if you are worried about flowers, a vegetable garden or a commercial garden such as strawberries, there are a few possible protective measures.

First, you need to understand there are two types of frost, radiative and advective. Radiative frost is the typical kind experienced on a clear, calm night. During this type of frost, calm conditions allow heat to escape into the atmosphere, cooling the lowest layers.

You can prevent frost damage by covering the crop, trapping the heat stored in the soil. Another method is to spray water on the crop. This works because water has a large amount of heat energy to release, which keeps temperatures warmer.

The third measure is to stir up the lower levels of the atmosphere. This can be done using fans or fires to create convection currents. Studies have shown that on radiational cooling nights, temperatures a metre or two off the ground can be as much as 2 to 5 C warmer.

The second type of frost, advective frost, is more difficult to manage. It occurs when a cold or sub-zero air mass moves into a region. It is usually accompanied by wind and lasts much longer. Since all levels of the atmosphere are cold, we cannot pull in warmer air, and since it lasts longer, using water will probably not work.

The only method left is to cover the crop and hope the sun comes out. Let’s hope we do not have to deal with late spring frosts this year.

The post Understanding early and late frosts appeared first on Manitoba Co-operator.

Manitoba received the most moisture from this system, with widespread 20 to 30 millimetres of rain mixed with snow. The northern half of agricultural Saskatchewan, along with the far eastern regions, also saw totals ranging from five to 15 mm. Parts of southern and central Alberta had precipitation, mostly as snow, with amounts ranging from four to 12 cm.

While this moisture is welcome, it will do little to alleviate drought conditions that have been developing across the Prairies for several years.

The last time we looked at weather data, I showed it in tables because it seemed the best way to get the information across. This time I created a series of graphs to tease out precipitation. I looked at yearly precipitation for two main centres in each province going back five years (2018-2023).

The first graph shows the precipitation anomaly for each location over those five years, done by adding up precipitation each year compared to the average amount for each year. What jumps out at me is the precipitation deficit in Regina and Saskatoon. Both locations have received 700 mm less than average. Calgary and Edmonton had much lower deficits, around 200 to 300 mm.

The second graph shows yearly precipitation totals for each location compared to average. What jumps out to me right away is that very few locations and years were above average, which shows why the Prairies have been slowly slipping into a longer-term drought.

The third graph shows precipitation at each location over the last five years. Like the first graph, it helps to visualize total amounts without considering averages. Of interest is that totals for Winnipeg, Brandon and Edmonton are close to each other and Calgary is only a little behind. As expected, Regina and Saskatoon received much less precipitation than the other locations, more than a metre less.

The fourth graph breaks total precipitation into yearly amounts. There is not a lot of difference between the years, but 2022 was a wet year for Winnipeg and Brandon.

There is no obvious cause for the build up of drought conditions, such as a couple of super dry years. Rather, the slow lack of precipitation over the past five years has brought us to this point.

We have also seen several summers with well above average temperatures across the Prairies, which increases evaporation and evapotranspiration and makes below average precipitation even worse It will take more than a couple of wet months to bring an end to the drought. Hopefully, with El Nino coming to an end, we will see a shift toward a wetter pattern.

The post The slow slide into drought appeared first on Manitoba Co-operator.

Last year, June had average temperatures equivalent to July’s, and July had average temperatures more like June. We didn’t quite see that in March, but in some locations, March was a little colder than February. The strange weather continues. March was colder than average by a few degrees in most locations, but not bone chilling. It seemed cold because February was so warm.

In Alberta, southern regions had some of the worst weather across the Prairies. Sorry Calgary region. We do feel sorry for you when this happens in spring. Looking at mean monthly temperatures, Calgary was the warm spot at-4.2 C, but that was about 2.5 C below the long-term average.

The Edmonton region was the cold spot, with a mean monthly temperature of -5.6 C, about 1.2 C colder than average. Peace River was slightly warmer, with a mean monthly temperature of -5.4 C ,which was 0.2 C warmer than average.

I use the international airport temperature for Edmonton and not the Blatchford site, which is what you see on Environment Canada’s website. If I used the Blatchford site, the mean monthly temperature for March was -4.2 C. I have had several people write to me, noting this site gives much warmer readings than the airport site.

Precipitation across Alberta in March ranged from very dry over northern and central regions to wet across parts of the south. This issue’s map shows the distribution of precipitation in March across the Prairies as a percent of average, but let’s look at the totals for our three main reporting stations.

Peace River was driest, with only 2.1 mm of water equivalent precipitation reported. Edmonton was almost as dry, with 6.1 mm. In the Calgary region, several storms brought significant amounts of precipitation, with the total at the end of the month at 57.1 mm, which is about 39 mm above average.

In Saskatchewan, Saskatoon recorded both the coldest mean temperature among the main reporting centres across the Prairies, and the coldest compared to average . Saskatoon’s mean monthly temperature was -9.1 C, which was 3.8 C below the long-term average.

It was a little warmer in Regina, which reported a mean monthly temperature of -7.3 C, or 2.5 C below average. Precipitation across both centres was a little below average. Saskatoon reported about 11 mm of water equivalent precipitation and Regina reported about 15 mm. Both values were about five mm below average for the month.

The Winnipeg region was the warm spot, literally and relatively, with a mean monthly temperature of -6.1 C. That is only 0.3 C below average. Brandon was a distant second with -8.5 C, which was 2.3 C colder than average. The cold spot was Dauphin, with -8.9 C, or 2.8 C colder than average.

Winnipeg recorded 9.4 mm of water equivalent precipitation and Dauphin reported even less at 4.7, both well below the average of 22 mm. Brandon had a monthly total of 21.2 mm, just shy of average.

Overall, it was a colder than average March and most regions had below average precipitation. As for forecast accuracy, the winners are CanSIPS and my forecast.

CanSIPS predicted “slightly above average temperatures across eastern regions in March with central and western regions seeing near to below average temperatures. Precipitation forecast is calling for above average amount over eastern regions in March with near average amounts over central and western regions.”

My forecast was this: “Eastern regions will see above average precipitation in March with western regions seeing near average amounts. Temperatures will be near to below average in March right across the Prairies.”

Now to the long-range forecasts. The Old Farmer’s Almanac calls for well below average temperatures in April and well above average precipitation. May is expected to see slightly below average temperatures and precipitation. June will see near to slightly above average temperatures and near to slightly below average rainfall.

The Canadian Farmer’s Almanac also calls for a cold and wet April follow by similar conditions in May. Its June outlook is for near average conditions.

NOAA calls for warmer than average temperatures over the eastern prairies and near average temperatures elsewhere in April to June. It predicts near average precipitation. The CFS model calls for above average temperatures, a trend most pronounced over northern regions. It predicts near to above average precipitation over the next three months.

The CanSIPS model forecasts above average temperature in April across all regions except southern Alberta. May and June are expected to see above average temperatures. Its precipitation forecast is spotty; essentially near average.

The ECMWF or European model calls for above average temperatures with near average precipitation, and Manitoba with a chance of above average amounts.

I think we will see near to above average temperatures over the next three months, and I lean toward the ECMWF model, which predicts near average precipitation and potentially above average amounts in the eastern Prairies.

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To tackle this question, we need to start with a review of the atmosphere. The lower part of the atmosphere is the homosphere, where concentrations of gases are consistent throughout this region. Remember, the prefix “homo” means same.

The heterosphere is the upper part of the atmosphere where the concentration of gases can vary greatly. “Hetero” means different. In terms of temperature, there are four regions or layers: the thermosphere, mesosphere, stratosphere and troposphere. One of these layers, the troposphere, is responsible for most of our weather.

This, combined with Earth’s incoming solar radiation, helps us understand why the sky is blue.

To begin, we need to look at what happens to the incoming shortwave solar energy as it comes into contact with Earth and then goes through the different layers of the atmosphere to reach the surface.

Earth receives energy from the sun in the form of shortwave radiation. When this energy is turned into heat, it takes on the form of long-wave radiation. A good portion of both types of radiation passes through our atmosphere.

Shortwave radiation that reaches the Earth’s surface is called insolation, and this is the driving force behind our weather. Insolation is comprised of shortwave radiation transmitted directly to the ground, along with diffused or scattered radiation. As shortwave radiation travels through our atmosphere, some of it interacts with gas, dust, pollutants, water droplets and water vapour, changing its direction or scattering it.

Why is the sky blue? This scattering of shortwave radiation causes the sky to be blue during the day. It is not the reflection of the oceans, as some might believe. This scattering is also why sunsets and sunrises take on a reddish hue.

The principle behind why we see these colours is known as Rayleigh scattering, named after the English physicist Lord Rayleigh, who came up it in 1881.

The principle links wavelength to the size of the particles that cause the scattering. The shorter the wavelength, the greater the scattering, and vice versa. This means small gas molecules will scatter shorter wavelengths of light, and with visible light, the blues and violets have the shortest wavelengths. Oranges and reds have the longest wavelengths.

Since most of our atmosphere is made up of small gas particles, the short waves of blue light are scattered, and the lower atmosphere, or homosphere, is dominated by scattered blue waves that make the sky appear blue.

Around sunrise and sunset, the angle of the sun means incoming solar radiation has to travel through much more atmosphere. During the day, sunlight travels from the top of the atmosphere to the ground at a fairly straight angle. This distance, or at least the distance it has to travel through the homosphere, is about 110 kilometres. This is relatively short, so only blue light is scattered.

During sunrise and sunset, the shortwave incoming solar radiation travels through a much thicker layer of the homosphere due to the shallow angle. This increases the distance to as much as 1,000 km. The short blue wavelengths are still scattered, but so much that only the longer orange and red wave lengths are left to reach our eyes.

So, it is the distance that light has to travel early in the morning or evening that makes the sky orange or red.

In addition to light scatter, shortwave radiation is also refracted as it enters the atmosphere. Refraction is the bending of light as it passes from one medium to the next. In this case, it passes from the virtual vacuum of space to our dense atmosphere and also through different temperature layers.

We have all seen examples of refraction. Rainbows are created when light passes through dense water drops, causing the different wavelengths of light to refract at different rates. Mirages are another example of refraction. Most of us have experienced mirages on warm days along a highway when you see what appears to be something floating above the road. In this case, the hot air above the highway causes refraction.

I mention refraction because without it, the amount of daylight we receive would be about eight minutes less each day. When the sun sets or rises, the light refracts as it passes from space into our atmosphere. This refraction allows us to “see” the sun when it is still below the horizon.

In the morning, we see the sun rise about four minutes before it actually moves above the horizon and at sunset we continue to see the sun for about four minutes after it has dropped below the horizon.

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Often when I discuss weather in what I refer to as the Dauphin region, I simply state that Dauphin can experience mild temperatures in spring thanks to its elevation. It was pointed out to me that this is misleading. Dauphin is in a bit of a valley east of the Manitoba escarpment, so its altitude at 268 metres is not that high. It’s a fair bit lower than Brandon, which is at 409 m.

When I discuss weather in the Dauphin region, I often mean the region west of Dauphin, which is much higher, with Duck Mountain at 831 m and Riding Mountain at 756 m. This elevation can impact temperatures because warmer air aloft is often pulled downward as it flows over higher elevations.

Next up is the rest of the temperature summaries for last month. They all paint February 2024 as the warmest February on record. I won’t go into details about minor differences between agencies, but there were a couple of interesting facts and predictions.

First, of the 239 countries and territories with meteorologic stations, 194 had at least one station report a monthly temperature record for heat in February. That is remarkable, at 81 per cent, and according to @extremetemp, no other month has ever come close to this.

On a more dire note, the world’s oceans have now seen 11 straight months with record-breaking average temperatures. There are predictions that all southern oceans will experience coral bleaching this year and it may be the worst coral bleaching event in history.

Let’s move to our main topic: spring forecasting and when heat will move in for good. The toughest part of spring forecasting is considering snow on the ground and how it will impact temperatures. In a typical year, when there is widespread and fairly deep snow cover, this can be a little easier. Even then, the forecast will often call for warm temperatures with highs of 6 to 8 C and then they don’t happen. Why do we see these types of forecasts?

Forecasts by Environment Canada, three to five days in advance, are generated solely by computer models. There is no human intervention or interpretation in these forecasts. While they can be good, they often exaggerate weather systems.

Also, even with the size of computers used today, the amount of data and computations that must be done are so enormous that not every variable can be modeled to the depth and precision necessary for a good forecast.

This is where the human factor used to step in. The models would generate a forecast and then meteorologists would analyze it and use the “art” of forecasting to make changes. The art of forecasting is an intangible skill that incorporates gut feelings and intuitions that people have and may never be duplicated in computers.

This missing art accounts for lack of precision in our medium-range forecasts and often gives rise to erroneous claims of balmy weather in early spring.

This year has been a bit of an anomaly. Snowpack varies widely across the Prairies, often over relatively short distances. Daytime highs are often warmer than forecasts as weather models struggle with the unique snowpack. The models tend toward a normal snowpack and so far, they’ve often underestimated temperatures.

Let’s go back to a regular snow year. Why do the models often over-predict warm temperatures, especially at this time of the year? The basic answer lies with the snow, literally.

How many of us have gone out on a warm spring day to the local swimming hole or lake? What did you experience? I bet if there was a wind blowing off the lake, you noticed how much colder it felt. The cold water and ice on the lake cools the air around it. The same thing holds true when there is snow on the ground.

Snow acts in several ways to keep temperatures down. First, snow is cold by definition. Changing a solid to a liquid requires energy and in this case the energy is heat. Also, snow is usually white and white objects reflect sunshine.

So, if we have a large area covered in snow, and above-zero air moving into that region, the snow itself cools the air that comes in contact with it. As the heat of the air interacts with the snow, that heat melts the snow instead of warming the air, and it takes a lot of heat to melt snow. In fact, it takes almost as much heat to melt snow as it does to bring water to the boiling point.

There will always be exceptions. If very warm air is pushed into our region and wind mixes up the atmosphere and prevents the snow from cooling the layer of air next to it, we can see some very warm temperatures even with good snow cover. While this is fairly rare, it does occur, especially where the topography helps to mix the air.

The effect of snow acting like nature’s air conditioner can easily be seen when you examine temperature records. Even if you had no idea whether there was snow on the ground or not, in most years just looking at daily temperature records will show you when most of the snow has melted.

For an area to get consistently above zero, there cannot be snow on the ground. In some years the effect is so dramatic that you can see a jump of five to six degrees in mean temperature over a couple of days as the snow finally disappears.

So, if you’re looking forward to warmer days that consistently stick around, relax and wait for the snow to disappear.

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