Reports were made saying this summer was supposed to be a drought year as the last two were. Environment Canada Meteorologist Natalie Hasell says a shift started to take place in the weather patterns in late April and definitely into May.

"I think our forecast originally actually had no dominant trend," says Hasell. "So, it could have gone either way. We were in drought conditions last year and the year before. And things shifted and we got a lot more precipitation than we were used to. I would still say some areas got quite a bit more than normal for the month of May. It gets wet for the month of June. Earlier this year, we were in El Niño conditions, which is one of the reasons the winter was so dry. The low pressure systems were following the jet stream, as they often do, and the jet stream had been pushed further north."

 

She notes this means that areas north of us received more precipitation and more cold weather. Hasell says the jet stream, having been pushed north, allowed warm air to make its way well into southern and even central and northern Manitoba on a regular basis. 

"El Niño typically doesn't affect us in the summer, but this is also a moot point because we are no longer in El Niño conditions. We are in neutral conditions. We don't have that forcing, placing the jet stream north of us all the time, so the shift happened. The jet stream ended up being further south than it had been. So basically, right over us. So, the low-pressure systems since late April have had many more tracks through Southern Manitoba than they had in previous months and possibly previous years."

She explains that resulted in more precipitation as the low pressure centres, themselves, travel over the area. Frontal structures also brought precipitation cooler weather at times.

 

"This meant more variability in the weather than we've seen in the last while. Looking at thunderstorms, low-pressure centres and frontal structures are definitely lifting mechanisms or triggers for vertical motion. We had the moisture, we had the instability quite regularly, and daytime heating also plays a role, sometimes destabilizing the atmosphere, sometimes being the trigger. So, sometimes, you don't even need an organized system. You can be in the middle of a warm air mass, and daytime heating can just do it all by itself."

She explains, seeing as we've already had precipitation, chances are it's going to cycle through, or at least increase the likelihood of, more precipitation, and increase the likelihood that storms will tap into this local moisture. 

"They don't need local moisture. You can get moisture coming up from the Gulf of Mexico. The local moisture adds to the entire thing, so the storms are going to be larger, the storms are going to last longer, the storms are going to be more severe, and dump more rain. It's the profile of the winds in the vertical -- wind shear, as we might call it -- that determines what kind of thunderstorm we get."

 

She notes having these first three elements -- the moisture, the instability, and a lifting mechanism -- we'll get thunderstorms. The wind shear determines the kind of a thunderstorm.  Hasell adds a number of events have taken place where the wind shear was right for the thunderstorms to grow large and become severe. 

"Our precipitation forecasts in the long term are not very good forecasts. It says so right on our site. Even more so, when you have a no dominant trend, the forecast is not useful. It doesn't tell you which way it could go. Unfortunately, that is the situation with our long-term forecast quite regularly."