With plenty of severe weather occurring all across the Canadian Prairies this summer, I thought we should go back and take another look at some of the aspects of severe summer weather.
The first thing that pops into my mind when it comes to severe summer weather is thunderstorms, which can bring several types of destructive weather. Heavy rain can cause all sorts of flooding issues. Lightning can range from being a spectacular light show, to starting fires, to actually killing people directly. Wind is probably the most widespread destructive force when it comes to thunderstorms. Whether the wind is simply a straight-line wind or the compact and deadly tornado winds, overall, wind probably causes the most damage.
Hail is one other type of severe weather that thunderstorms create. If you have spent any significant amount of time living on the Prairies, then you have probably experienced a hailstorm. While hail can occur pretty much anywhere across North America, there are two main regions where the chance is significantly higher – the central United States and the Canadian Prairies, and in particular, Alberta.
Temperature and hail
Can it be too warm for hail? Yes. If the upper atmosphere is warm, then the freezing level in the atmosphere is very high. If a thunderstorm does develop, and if hail forms in the storm, chances are that the hail will melt well before it ever reaches the ground. So, the key ingredient for hail to form is to have plenty of cold air aloft and to make sure it is not that high off of the ground.
Let’s back up for a second. I need to touch on one of my weather peeves which, you guessed it, has to do with hail, or rather, the improper use of the term hail. Hail refers to the falling of ice from a cumulonimbus (thunderstorm) cloud. Ice pellets, snow pellets, and graupel (a snowflake that has been coated in ice) are not hail and should not be called hail. These types of precipitation will often occur in the spring or late fall and are not associated with thunderstorms.
OK, now back to our thunderstorm with low-level freezing.
Most thunderstorms will produce hail, the question is, whether the hail will grow large enough to make it to the ground without completely melting. As we have already discussed, 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 everyone 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, here is where a second common misconception about thunderstorms and hail lies. 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. If that hailstone just kept going up towards the top of the thunderstorm it wouldn’t accumulate much more ice and 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.
When it comes to hail, size really does matter. Pea-sized hail will do little if any damage to structures and 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 don’t 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 regards to weather, hail has by far the most descriptive measurements.
To end off this issue’s article here are some of the more common descriptive terms used for hail and the approximate size that hailstone would be.