TABLE 1. Twelve largest recent Canadian hailstorms (losses in millions of dollars)
Sept. 1991 Calgary 343
July 1987 Edmonton
June 1995 Winnipeg
May 1987 Montreal
July 1992 Calgary
The Weather Vane is prepared by Daniel Bezte, a teacher by profession with a BA (Hon.) in geography, specializing in climatology, from the University of Winnipeg. Daniel has taught university-level classes in climate and weather and currently operates a computerized weather station at his home near Birds Hill Park, on 10 acres he plans to develop into a vegetable and fruit hobby farm.
Contact him with your questions and comments at [email protected]
So far we have not seen a lot of thunderstorm activity this year, although in reality we are really just entering into our main thunderstorm season. We discussed tornadoes in our last few articles, but back in April I promised to discuss hail, so hail it is!
The first question when it comes to thunderstorms and hail is, “Can it be too warm for hail?” The answer is yes. If the upper atmosphere is warm, then the freezing level is very high up. If a thunderstorm does develop and if hail forms in the storm, chances are 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’s not that high off the ground.
Let’s back up for just 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 refers to the falling of ice from a cumulonimbus (thunderstorm) cloud. Ice pellets, snow pellets and graupel (snowflakes that have 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 prevent a hailstone from melting before it hits the ground is to start off with a really big hailstone!
Now, here is another common misconception about thunderstorms and hail: 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 will freeze 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 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.
The biggest hailstone ever recorded fell in Nebraska in 2003 and measured seven inches in diameter (a softball is about 4.5 inches in diameter)! The heaviest hailstone ever recorded fell in Kansas and weighed in at 1.67 pounds. On a more global scale, in 1983, hailstones reportedly as heavy as 2.2 lbs. fell in Bangladesh. It has been estimated that hailstones this large hit the ground travelling at nearly 100 m. p. h. (160 km/h)! The storm in Bangladesh resulted in 90 fatalities.
So how does a hailstone stay up in the air and travel within the thunderstorm? The answer is updrafts – extremely powerful updrafts. These rising currents of air can keep these massive hailstones aloft until the updraft either dies out or the hailstone falls out of the updraft and comes crashing down to earth.
While most us have experienced hailstorms, and some of us have even been caught in a really severe one, I don’t think anyone living in agricultural Manitoba has ever experienced a hailstorm lasting 85 minutes and covering the ground to a depth of 46 cm! This is what happened in June of 1959 in the town of Selden, Kansas. When it comes to Canadian hailstorms, Alberta is the hail capital, with most of our country’s hail records occurring there. If we look at the top 12 Canadian hailstorms from the aspect of cost (Table 1), we can see that, with the exception of two storms, all of them occurred in Alberta.
After seeing this I’m not sure why anyone would want to move to Calgary!