Unfortunately this week could be a pretty good preview for the summer, or at least for the first part of the summer. The trough position that Bigmt has noted keeps weak low pressure systems in the area, along with some cooler upper atmosphere temperatures. As we move into the warmer periods of the year with peak sunshine and daylight heating, weak low pressure storms tend to be more common than the stronger low pressure systems you seen in the fall, winter and spring. With the daytime heating that occurs from the sunshine warming the lower levels vs. the very cold upper atmosphere you often see these brief convective storm out around a low pressure systems.
Today is good example, take a look at the GFS model that has weaker low pressure system (noted as the red LP) in Northern Ontario with convective scatted storms out to the east and south of the low where warmer air can mix with the colder upper atmosphere (circled with purple):
You can also see this example in the latest satellite image:
If we continue with the trough pattern and weaker low pressure system, many of our summer days could be mixed like this with sunshine in between scattered storms.
The good news is the weak low pressure pattern appears to relax a little on Saturday so most Ontario enjoys a nice day. However it’s back again late Sunday through Ontario with more scattered rain:
The other good news is the Euro weeklies look to relax the pattern a little come mid to late month allowing some warmer more humid air to set up across Southern Ontario out to the Maritimes. Let’s hope the longer range beyond that doesn’t bring the trough pattern back.