TABLE 1. RAINFALL FROM 6 A. M. FRIDAY TO 6 A. M. SATURDAY
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]
Last weekend we finally saw some thunderstorm activity, but there was little in the way of really severe weather, unless you consider heavy rain part of “severe weather,” and if you ask me, it is.
Thinking back over the last few months I seem to remember some weather dimwit saying we should expect to see hot, dry conditions this spring and summer. Well, I’d like to have a few words with that person – wait, I think that dimwit was me!
After a really warm March and April we have seen a mixed bag of weather in May. The first part of the month started off cool and a little on the wet side. We then saw summer weather move back in during the middle of the month. The month ended on a very soggy note, with several locations breaking daily rainfall records last weekend.
So just what happened last weekend to bring us all the rain? A trough of low pressure developed to our west and this trough was able to tap into moisture from the Gulf of Mexico. This Gulf moisture streamed north ahead of the trough of low pressure and a warm front lifted north with it. This warm front then stalled out over southern Manitoba over the weekend. Temperatures to the south of the front were in the upper 20s to the low 30s while north of the front, temperatures struggled to reach the upper teens.
The push of warm, moist air was so strong, it overran the surface front and spread warm, moist air overtop of the front northward. This warm air aloft was warm, moist and deep enough to allow elevated convection to develop – in other words, it created the right conditions for thunderstorms. The real problem came from the fact that the trough of low pressure and frontal boundary didn’t move much over the weekend and ended up bringing us several rounds of severe weather.
Some areas did experience some hail and really high winds, but the biggest severe weather punch came from the rain. I know at my place I had never seen rain come down as fast and hard as it did late Saturday afternoon. At one point I couldn’t see more than about 100 feet. While my area did end up turning into a big lake, with the local creek spilling over its bank and across roads for the first time in memory during the summer months, my region was not the hardest hit. The rainfall amounts in Table 1 were reported by Environment Canada for various times and locations across southern Manitoba last weekend.
I’ve been teaching my students at school how to calculate volume over the last couple of weeks, and we tackled a problem like this late last week: just how much rain actually fell this week? Well, the amount of water that fell over southern Manitoba is just staggering. Southern Manitoba covers an area of about 60,000 square kilometres, and over this region I would say that by looking at the numbers above, that we probably conservatively averaged between 25 and 35 mm over this whole region. When we do the math on these numbers, we come out with a mind-numbing 1.5 to two cubic kilometres of water or nearly two billion cubic metres, which, converted to litres, would be two trillion!
To put that into perspective, on average Manitobans consume roughly four million litres of water per year. Another way to look at this amount is that it is about 15 per cent of the total volume of Lake Manitoba.
Next week we will take a full look back at the month of May and peer ahead to see if we will indeed have a warm, dry summer.