A broad trough currently located along the Ontario/Manitoba border this morning will push eastward through the day today. Associated with this trough is a surface low pressure which is currently located near the Lake Nipigon region. Associated with this low are several waves, with the leading warm front pushing through this morning which is bringing an area of showers and thundershowers to southwestern Ontario this morning. These showers/thundershowers are expected to clear out through the morning hours.

In terms of timing with the frontal passage, models are in pretty good agreement with a late afternoon/evening event. A few convective models do paint a little bit of a different picture. The WRF does indicate a pre-frontal line of storms mid-afternoon which does eventually give way to a line of storms. The reason why I am pointing out this particularly model solution is the fact that it hints art what could be a few isolated storms before a large line develops. With low level shear in the 20-30 kt range at this time, these storms could have the potential to develop a brief tornado. But this scenario looks to be the outlier at this point in time but can’t be ignored as it has initialized very well with the morning scenario.

Most models look to be trending toward a line of storms breaking out along the front from the Nickel Belt region straight through to extreme SW’rn ON. I believe this is the more likely scenario as shear vectors are just about parallel to the cold front which will favour more of a linear storm mode and not so much isolated supercells. But again with low level shear forecast to be 20-30 kt, surface winds from the south to even slightly southeast, and lake breeze interactions, cannot rule out the risk of a few brief, weak tornadoes. Thus thinking some sort of QLCS (Quasi-Linear Convective System) type spin up could be possible, very similar to landspout type tornadoes. Instability parameters are not ideal with SBCAPE values forecast to be between 1000-1500 J/kg from the southern tip of Georgian Bay-London-Windsor region, hence the very minimal risk of brief/weak landspout type tornadoes.