As we have an early deadline this week due to Canada Day, I won’t be able to do the monthly review and the look ahead at what July might have in store for us until next week. I know you are all disappointed about this, but there is nothing I can do about it – honestly.
Last week’s article ended by discussing caps (not the ones you wear on your head) and how they come into play with severe thunderstorms. As I am writing this on Friday June 26, I am crossing my fingers that the cap on the atmosphere will last long enough for my son’s outdoor birthday party to go off without having to worry about thunderstorms. In this case, a cap will be in place during the day, but as the day wears on, colder air in the upper atmosphere will be slowly pushing eastwards across southern Manitoba.
This colder air in the upper part of the atmosphere will replace the layer of warm air that is creating the cap which is preventing the surface air from rising high enough to create thunderstorms. Once that layer of warm air starts to get pushed out, our cap will start to weaken and eventually – bang, thunderstorms will start to fire up as all of the energy building up during the day gets released.
So let’s see, in order for thunderstorms to form we have learnt that we need warm, moist air to rise up into the atmosphere and that the warm temperature is a relative term. That is, we need the rising air to be significantly warmer than the air around it. So we can still get thunderstorms on cool days, if the air above us is really cold. We also learned that we need some way of venting that rising air at the top of the storm, or all that air will eventually pile up in the upper atmosphere and then come crashing back down, snuffing out the storm in the process.
We then found out that if we can get a storm to start rotating by having winds blowing in different directions as you move up in the atmosphere (wind shear), the updrafts and downdrafts within the storm will stay separate for a long period of time, thus allowing for strong, long-lasting thunderstorms. Finally, we talked about atmospheri c caps which act like lids storing up energy and then releasing that stored up energy all at once.
Now, is that it when it comes to the ingredients that can combine together to create strong thunderstorms? Well believe it or not, this pretty much sums it up. What makes one thunderstorm more severe than another storm depends largely on how these different ingredients come together. The general rule of thumb is that the higher the values on each of these four ingredients, the stronger the potential storm. The one exception to this might be the cap, as if it is too strong, then any and all convection will be limited and we will not see any thunderstorm development.
Also, we can have high values in all areas and you will still not see severe thunderstorms. The first reason is that once one or two storms get going they act like vacuums, sucking up all the heat and moisture around them. The bigger the storm, the larger the area it will pull from. This can then act to prevent storms from developing elsewhere.
Secondly, all these ingredients have to come together at just the right time and amount. Too early in the day and our rising air will not be that strong. Too much rotation and the storm can be sheared apart. Not enough moisture and the storm will not last long enough to become severe. The venting at the top of the storm comes a little too late and a downdraft wipes out the storm.
Severe thunderstorms can be a delicate recipe for Mother Nature and the vast majority of time she doesn’t quite get all the ingredients together in the right amounts and combine them at the right time, but when she does, boy oh boy can it be an incredible thing!
Next week we will take our look back at June’s weather and peer ahead to July and August to see if we will continue to receive our payback for the crappy spring weather we received this year.