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Will Hailstorms be More Common on the Prairies in the Future?

Will hailstorms be more common on the Canadian Prairies in the future? That question was posed by atmospheric scientists from Environment and Climate Change Canada and the University of Manitoba in a recent article titled “The changing hail threat over North America in response to anthropogenic climate change” in the journal Nature Climate Change.

Disclosure: I was involved in writing some of the code used for the data analysis in this study (see article acknowledgements). However, I was not an author of this publication and the opinions below are my own.

This study examined changes in hail across North America using three climate models that simulated future conditions between 2041 and 2070. The model was used to study changes in hail size, frequency, and seasonality. Interestingly, there was not a single uniform trend in hail across all of North America. Some parts of North America, like the southeastern United States, appear likely to see less hail due to higher freezing levels in the atmosphere. Higher freezing levels cause hail to melt before hitting the ground, reducing the size of hail stones, or eliminating them completely. Other parts of North America, like the front range of the Rocky Mountains, will probably see more hail. However, for large parts of the continent, the study found no clear trend in the number of future hail events.

Another aspect of the study examined how hail size will change in the future. In the spring, the study showed most of North America receiving larger hail, but in summer some parts of the continent will likely see larger hail, while other parts see smaller hail. This is again due to increases in temperature in some regions, which will cause hail to melt more before hitting the ground.

The last aspect of the study looked at whether the peak in hail season will change. In most of Canada peak hail season is June or July. This isn’t expected to change much on the Prairies, but in eastern Canada there does appear to be a slight trend towards an earlier peak in the hail season.

This study is quite interesting, because it’s one of the first to look specifically at how hail will change in the future. Many past studies have just examined at how severe weather in general will change, but didn’t examine the specific impacts. While this study provides good insights into future hail trends, I’ll just add one cavaet; this is only one study based on three model simulations. In science it’s important to have as much coroboration as possible for your findings. For that reason, I wouldn’t put all my proverbial eggs into this one study’s basket. I expect that we’ll see more hail studies in the future that can be compared to this article. Once we see additional research on this topic, we can determine whether we’re seeing the same trends in all the various studies, or if there is still uncertainty in future hail trends.

-Scott


Weatherlogics has Canada’s most comprehensive hail database. We are also experts in meteorological research and can provide highly specialized research to meet your needs.

 

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

One frequent question we get is: “What’s the difference between a tornado and straight-line winds?” In today’s blog we explore that question.

According to the American Meteorological Society (AMS), a tornado is:

A rotating column of air, in contact with the surface, pendant from a cumuliform cloud, and often visible as a funnel cloud and/or circulating debris/dust at the ground.

A tornado can often be clearly identified as a vortex of rotating air extending from the cloud to the ground.

You’ve no doubt seen a picture of a tornado before, they are often very photogenic and frightening. Tornadoes are essentially just a highly concentrated area of wind that is rotating around an axis. So what makes that different from straight-line wind damage? According to the AMS, straight-line winds are:

Used in the context of surface winds that inflict damage; to be distinguished from winds in tornadoes, which have significant curvature.

Damage from straight-line winds is often severe and can look like tornado damage. Image from NOAA.

Both tornadoes and straight-line winds are usually produced by thunderstorms, which adds to the confusion. While it is sometimes obvious when a tornado has occurred (you can often see them coming!), it’s not always. Sometimes the tornado is wrapped in rain and you don’t know it’s coming until it strikes. If a thunderstorm produces severe wind damage, such as ripping the roof off a house, it is not uncommon for a tornado to be immediately pinned as the culprit. However, it’s not that simple. Straight-line winds of some magnitude occur with virtually every thunderstorm, because they are associated with cool air descending out of the storm. Those winds are not always severe, but they are far more common than tornadoes. The key difference between tornadoes and straight-line winds is that straight-line winds are not rotating.

So, how can you tell the difference between a tornado and straight-line winds? Here are some things to look for:

  • Was the damage very localized? Was one house completely destroyed, but the one beside it was seemingly untouched? If so, it’s probably a tornado. Straight-line winds tend to occur over a relatively large area, making it unlikely that there would be such a dramatic difference in damage over a short distance.
  • Is debris scattered around randomly, or does it follow a clear direction? Tornadoes tend to toss debris all over the place, whereas straight-line winds will blow everything in one direction.
The trees are laying in many different orientations, an indication of tornado damage. Image from NOAA.
The trees are all laying in the same direction, an indication of straight-line wind damage. Image from NOAA.

Straight-line winds have been known to exceed 150 km/h, easily strong enough to cause severe structural damage. The weakest tornadoes usually have wind speeds of only around 100 km/h. However, the winds in the strongest tornadoes can exceed 300 km/h. The fact that weak tornadoes and straight-line winds often have wind speeds of comparable magnitude is another reason why they often get mixed up.

Ok, so we’ve established what tornadoes and straight-line winds are, but how about plow winds, downbursts, microbursts, and squalls? Actually, these are all just other words to describe straight-line winds. While there are some technical differences between those terms, they are all forms of non-tornadic winds, usually lumped into the category of straight-line winds.

So next time you hear about wind damage on the news, impress your friends – tell them the difference between tornadoes and straight-line winds!