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Hail and other damaging summer weather

Alberta’s topography makes it more prone to hail than, say, Manitoba

Picture a popcorn machine — or better yet, an old-fashioned bingo machine. The balls, or hailstones, are continually moving up and down due to the strong updraft.

Last article we talked about summer heat waves and tied in the idea that heat is a form of severe summer weather. Not too long after that, I came across an article that listed the deadliest summer weather across the United States and, you guessed it, heat-related deaths came in at No. 1. Sure, tornadoes and severe thunderstorms get most of the news, but heat waves can be slow and relentless killers.

Also in the news over the last week or so is the ongoing drought across much of the western U.S. One story in particular caught my eye, namely the level of Lake Mead hitting a historic low. Lake Mead was created in the 1930s by the building of the Hoover Dam, which backs up water from the Colorado River. Water levels in this reservoir have fallen 42.7 metres since 2000 — that’s right, metres — that’s over 130 feet! It is reported that if levels do not improve by August, mandatory water cuts will be placed on Nevada and Arizona by the winter, with California facing mandatory cuts shortly afterward. If you want something new to lose sleep about, imagine what people will start to do if drought and water shortages continue and even worsen. Canada’s water starts to look more and more tempting. You need water to live, and people will do almost anything if they run out.

Now, before we continue our look at severe summer weather, I have been getting a few questions about how the new weather station has been running. So far, I have to say things have been close to perfect with the station. For those of you who do not know, I bought an Ambient Weather WS-5000 station. I installed it in late winter/early spring, then moved a couple of sensors around once things warmed up. Since then, the sensors have all been happily reporting their data with almost no drops or data loss. I still have my old Davis station working, which allows me to compare some of the data. While the stations are not side by side, they both report temperatures and dew points within a degree or so of each other, which is a good sign. In the last thunderstorm, the Ambient station reported 36.7 mm of rain, the Davis station reported 35.8 mm and my manual CoCoRaHS rain gauge reported 37.6 mm. With all three reporting very similar amounts, I would say the accuracy of the new station is pretty good. The only gripe I continue to have are the shipping and handling fees if I want to get new sensors. The additional sensors themselves are fairly cheap, but I think I will wait until the border reopens to get them.

On the rocks

Now, on to more severe summer weather. We have talked about heavy rainfall and heat waves and have now experienced both events. Next up: hail.

Most thunderstorms will produce hail; the question is whether the hail will grow large enough to make it to the ground without completely melting. Having a very low freezing level helps this happen, because the hailstone only has a short distance to fall through the relatively warm air. Another way to keep a hailstone from melting before it hits the ground is to start off with a really big hailstone! This is one of the main reasons Alberta sees so much hail compared to everywhere else in Canada. The topography of Alberta is such that while ground temperatures can be really warm, the freezing layer is not that high up relative to what it might be in Manitoba.

Now, to get really big hailstones, you do not necessarily need a really tall (or high) thunderstorm. Hail forms when a particle passes from the warm (liquid) part of the cloud into the cold (freezing) part of the cloud. When this occurs, any water on the particle freezes and you now have a small hailstone. Now, if that hailstone just kept going up toward the top of the thunderstorm, it wouldn’t accumulate much more ice, therefore it would remain small. For hailstones to get really big they must go back into the warm (liquid) section of the storm, pick up more water, then go back up into the cold section of the cloud so the water can freeze. Repeat this cycle a number of times and you can get some really big hailstones. Picture a popcorn machine — or better yet, an old-fashioned bingo machine. The balls, or hailstones, are continually moving up and down due to the strong updraft.

When it comes to hail, size really does matter! Pea-sized hail will do little if any damage to structures or plants, while golf ball-sized hailstones can literally destroy everything in their path. When it comes to measuring hailstone size, things become a little strange. That is, you do not usually hear that the hail will be around 50 mm in diameter. Instead, you hear that the hail was the size of a golf ball or an egg. Of all the things we measure in regard to weather, hail has by far the most descriptive measurements. The table here lists some of the more common descriptive terms used for hail and the approximate sizes those hailstones would be.

So far during this summer’s severe weather season I haven’t seen or heard about any significant or large hailstorms. Let’s hope that continues for the rest of the summer.

About the author

Co-operator contributor

Daniel Bezte

Daniel Bezte is a teacher by profession with a BA (Hon.) in geography, specializing in climatology, from the U of W. He operates a computerized weather station near Birds Hill Park.



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