September 7th 2019 happened under nearly due SW flow.... And ended up as one of the best lightning shows in the city's history. I still have fond memories of that storm... If we want another storytime with Aidan tonight...
It's more about the differential flow aloft and getting midlevel moisture in early enough before the steep lapse rates associated with existing ridging make way for moister, warmer westerlies above 700mb. SE flow is the most common way we get that but it's feasible with other flow directions under the right conditions.