Forecasting Summer Weather on the Prairies

Forecasting summer weather on the Prairies is one of the great challenges in meteorology. Summer weather is volatile, ranging from searing heat, to vicious storms, to cool outbreaks of polar air. Northern parts of the Prairies can be experiencing heavy snow, while southern parts experience hot and stormy weather. So, why is the weather on the Prairies so crazy?

Summer weather on the Prairies can be volatile.

The Prairies are a confluence of regions; the arctic to the north, mountains to the west, and the boreal forest to the east. With the exception of the Rocky Mountains in Alberta, there are no features to block weather from coming across the Prairies. That means it’s easy for frigid arctic air to plunge down from the north, or for hot and humid air to surge up from the southern United States. The oceans can be a moderating influence on weather, keeping it from getting too hot or too cold, but the Prairies are far from oceans, making them susceptible to extreme weather. That means the Prairies experience a true continental climate, which is a climate of extremes – cold in the winter and hot in the summer.

It might seem like the Prairies feature a fairly uniform climate, but if you look closely there are actually many variations. In Calgary, the average temperature in January is -7.1 C, almost ten degrees warmer than Winnipeg, where the average temperature is -16.4 C. This difference in temperature exists despite the fact that Winnipeg is actually farther south than Calgary. One of the main reasons why Calgary is warmer than Winnipeg in the winter is because Calgary experiences chinooks; a warm wind that descends from the Rocky Mountains. Since Winnipeg is far from any mountain ranges, it is difficult to remove the dense, cold, arctic air mass that often settle over the city. However, the tables are turned in July, when Winnipeg’s average temperature is 19.7 C, versus only 16.5 C in Calgary. Calgary’s higher elevation of 3557 feet (783 feet in Winnipeg) puts it at a disadvantage when trying to achieve warmer summer temperatures.

Average annual temperatures across the Prairies using 1961-1990 data (image from Natural Resources Canada).

Surprisingly, precipitation is also quite variable across the Prairies. Calgary receives 418.8 mm (16.5″) of precipitation per year, which is over 100 mm (4″) less than Winnipeg (521.1 mm; 20.5″). However, the near-desert region around Medicine Hat in southeastern Alberta only receives 322.6 mm (12.7″) of precipitation per year, nearly 200 mm (8″) less than Winnipeg.

Average annual precipitation across the Prairies using 1961-2010 averages (image from Natural Resources Canada).

There are a number of factors that make predicting summer weather on the Prairies so difficult. One of the main reasons is that the jet stream is weaker in summer than in winter. This makes it more difficult for meteorologists to predict the long-term evolution of the jet stream because weaker jet streams often behave more erratically. In winter, the jet stream is strong, and therefore it is easier to predict its evolution. There is also a stronger connection between the jet stream to other global features in winter, like sea-surface temperatures (you may have heard of ENSO). Another reason why summer weather on the Prairies is hard to predict is thunderstorm activity. Thunderstorms develop almost every day across the Prairies in summer and trying to predict where they will develop is extremely difficult. It is not uncommon to go from blue skies to a raging thunderstorm within an hour or two and trying to predict when and where that will happen is nearly impossible. Sometimes these thunderstorms will also merge together, forming large convective weather systems. These convective weather systems can travel great distances, producing heavy rain and severe weather.  Such convective weather systems are actually very important to agriculture, because 30-70% of precipitation in summer on the Great Plains of North America has been attributed to thunderstorm activity (Fritsch et al., 1986).

The jet stream, shown as red arrows, tends to shift farther north and become weaker in the summer (image from Environment and Climate Change Canada).

However, there are ways to get better weather information. Firstly, it’s important to recognize the source of your weather data. If you’re just getting your forecasts online or from an app, chances are the forecast is mostly or completely automated. In other words, a computer is producing the forecast with little to no human intervention. This presents many problems, because computers often make large mistakes when trying to predict complex weather events. Only professional meteorologists can carefully analyze computer output and modify it towards a better solution. Unfortunately, there are few forecasts available that are reliably made by actual meteorologists. For example, Environment Canada’s meteorologists produce the first two days of their forecasts, but rely exclusively on computers for the rest of the forecast. Since these computers update four times per day, you can see wildly different forecasts from one hour to the next, never mind from one day to the next!

Weatherlogics’s meteorologists produce all of our forecasts, cutting out computer automation. This has resulted in great improvements in accuracy. For example, in May 2017 our forecasts were 50% more accurate than other common weather agencies in Canada. If you’d like to learn more about what we have to offer, get in touch!

References

Environment and Climate Change Canada: Weather at a glance (accessed June 19, 2017): https://weather.gc.ca/jet_stream/index_e.html

Fritsch, J. M., R. J. Kane, and C. R. Chelius, 1986: The contribution of mesoscale convective weather systems to the warm-season precipitation in the United States. J. Appl. Meteor. Climatol, 25, 1333–1345.

Natural Resources Canada: Introduction – Prairies (accessed June 19, 2017): https://www.nrcan.gc.ca/environment/resources/publications/impacts-adaptation/reports/assessments/2008/ch7/10381

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