I am proud to be the newest Snowlover on the blog! My other blog will continue to feature a de facto archive of severe weather reports from ON and QC from 2016 as well as my local weather statistics.
Strong elevated thunderstorms with small hail and torrential downpours. will likely develop between Windsor, London, and Niagara Falls on Sunday afternoon. These storms will likely attain supercellular characteristics in the strongly-sheared environment, but will not produce tornadoes or damaging winds due to a large-scale temperature inversion.
As for Monday, there are two potential scenarios, which both involve convection and heavy rainfall.
Before the possibilities diverge, it appears that Montreal will receive over 25-35 mm of cold rain on Sunday night, with temperatures falling to near 1 C before substantial WAA occurs. Freezing rain or even snow could fall in the Laurentians and the Eastern Townships before a transition to rain.
Scenario 1: Depicted by American guidance. Surface warm front gets stuck at Cornwall before occlusion. Thunderstorms move in Monday night with torrential downpours and frequent lightning with up to 1000 j/kg MUCAPE. 650 mb saturated freezing level and 1.4″ PWATs should increase precipitation efficiency but will likely eliminate hail potential. An inversion, again, prevents damaging winds from occurring. No updraft will be strong enough in that environment to break a 10 C inversion and bring a 90 km/h jet at 750 m AGL to the surface.
Simulated radar image from the 06Z 3K NAM at 2 pm Monday. Non-severe storms move through E and S ON at this timeframe.
Scenario 2: Depicted by the Canadian models. Surface warm front moves into the Ottawa Valley east to Trois-Rivieres on Monday afternoon and temperatures surge into the 20s in Ottawa, Montreal, and Cornwall with dewpoints approach 21 C. Cold frontal squall line is about 6 hours faster (8 pm vs 2 am) and could produce damaging winds with decent low-level lapse rates near 7 C/km complete with some mid-level dryness ahead of it. I’m unaware of potential CAPE values but they look pretty high in E ON so I wouldn’t discount other severe threats if it does come to fruition.