Severe storms loom for parts of Ontario, risk of brief tornado
Thursday, July 18, 2013, 12:23 -
We've been watching the models closely this week with regards for the potential for severe weather in Ontario.
We're expecting off and on thunderstorms through the day on Thursday as well as Friday and Friday night.
When we have a cold front moving into a hot, humid, unstable air mass, thunderstorms are almost a guarantee.
What is hard to guarantee though is "who" will see the thunderstorms.
Models are agreeing that Friday will hold the potential for fairly severe storms across Southern Ontario.
Timing on the passage of the cold front varies among forecast models. It would appear that the environment ahead of the cold front on Friday will be conducive to isolated thunderstorms first.
The main frontal storms will then come through later in the day toward the evening hours. The tornado threat is low, but certainly not zero chance.
You need the right ingredients to get tornadoes, namely wind shear and instability. It is possible that if storms manage to initiate (spark up) ahead of the main front on Friday, a few may have the potential to produce a brief tornado. This risk is greatest in vicinity of the lake breezes that will set up off the lower Great Lakes. This is because these lake breeze boundaries help to enhance the wind shear (as previously mentioned as a main ingredient for tornadic development).
Once the main front comes through bringing storms with it, the main threat aside from lightning and heavy rain will be straight-line winds.
The heat and humidity we have been experiencing this week provide the necessary energy (or fuel) for thunderstorms. The abundance of moisture in the atmosphere in a necessary ingredient for thunderstorm formation.
It should be said that with all of this moisture available, heavy rain and torrential downpours are a risk with these storms as well.
Due to the upper level dynamics in place, the storms should not remain stationary but that's not to say they couldn't drop a lot of rain in a short period of time. We don't expect a repeat of the flooding that occurred last week, but localized flooding is always a risk with severe thunderstorms.
Once the cold front moves through, we can expect some much needed relief across southern Ontario. It will be most noticeable Saturday night and Sunday. Temperatures will return to more normal values. There will still be a touch of humidity, but values will be in the low 30s for some areas as opposed to the low 40s which we have been experiencing this week.
With files from Brad Rousseau