A record-breaking Colorado Low is moving across Northeastern Ontario this afternoon with moderate to heavy snow to the north and scattered showers and thunderstorms towards the south.
Along a cold front trailing with this system, we may see some isolated severe thunderstorms across the Extreme South extending towards Southwestern Ontario. The majority of the severe thunderstorms will be positioned over the Ohio, Tennessee and Mississippi Valleys where multiple tornadoes have already been confirmed.
Blue or '1':
Areas in the blue or marked with a '1' can expect mainly non-severe thunderstorms. Non-severe thunderstorms are expected to bring wind gusts between 50 and 70km/h, locally 80km/h as well as heavy rain producing 15 to 30mm of rain, locally higher. Frequent lightning is possible across Southwestern Ontario extending into the GTA. Small hail between 0.5 and 1cm is possible. There is a low risk of severe thunderstorms extending slightly passed this area into Woodstock or Grand Bend although this is highly unlikely. There is also an area east of Lake Huron extending from Kincardine through Huron and Perth Continues into the Woodstock area which may also see some severe thunderstorms. Based on the location next to Lake Huron, the chance of severe thunderstorms is too low for even the 'low' risk area.
Green or '2':
Areas in the green or marked with a '2' can expected a low risk for severe thunderstorms. This includes Lambton, Elgin and Essex Counties as well as portions of Middlesex County (including London) and the Region of Chatham. Severe thunderstorms are likely to develop across Michigan but weaken upon entering Ontario due to the frigid surrounding lakes. Areas around Essex County are most at risk of seeing some severe thunderstorms including the risk of an isolated tornado. The tornado risk is quite low but not-zero and is highest near the Detroit River. A tornado is unlikely today although it's worth mention the risk. We have highlighted the tornado risk area with an 'Area of Interest'. It's questionable how far inland the severe storms reach as it's questionable if they will even affect Ontario at all. The main risks include frequent lightning, gusty winds between 70 and 90km/h, small hail between 0.5 and 1.5cm as well as haevy downpours producing 20 to 40mm of rain.
Snowfall and Rainfall Forecasts:
https://www.weatherwatch.space/post/record-breaking-colorado-low-weakening-into-ontario