Drenching Rain for Southern Ontario Over the Weekend; Locally Up to 100mm of Rainfall Possible

Don’t forget your umbrella if you plan to be outside this weekend! Mother Nature is planning on turning on the taps across Southern Ontario as an active storm track sets up across the region and pumps significant amounts of moisture over the next few days. There will also be the potential for embedded thunderstorms within all this moisture which will only further increase the rainfall totals over the next 72 hours.

By the end of the weekend, we could be talking about triple-digit rainfall totals with the hardest-hit regions seeing between 50-100mm and perhaps locally up to 125-150mm. The focus for the highest totals will be on the Lake Huron shoreline through Central Ontario and into parts of Eastern Ontario near the Quebec border with lower amounts the more south/east or north/west you go.

If you aren’t a fan of the rain, the good news is that this won’t make a mess of the entire weekend and there will be short dry slots between the multiple rounds of rain over the next few days. The rain has already started across Southern Ontario with moderate to heavy rainfall throughout the day on Friday. This is expected to linger into the overnight hours before tapering off somewhat early Saturday morning, but scattered showers may linger around especially through Eastern Ontario.

Although the break will be short-lived as more moisture builds in from the west by Saturday afternoon. This wound could bring some quite intense and potentially near-severe thunderstorms during the evening hours on Saturday for regions east of Georgian Bay. At a minimum, these storms will pack a punch with very intense rainfall rates and some ‘training’ potential where the storms line up for hours over a particular location. Some stronger wind gusts and moderate-sized hail could also be associated with some of the more intense storms, but the exact severity remains unclear. This will be covered in a separate thunderstorm outlook for Saturday to be issued late Friday.

This heavy rain will continue throughout the overnight hours on Saturday and into Sunday morning with the bulk of the precipitation to the north of the GTA affecting Central and Eastern Ontario. It should move out of the province by Sunday mid-morning and allow for a fairly dry day on Sunday with the exception of some scattered showers and pop-up thunderstorms near Lake Huron towards the evening on Sunday. More rain will continue on and off for the early part of next week although we’re not expecting anything widespread or intense so we won’t be including it in this forecast.

The map above should give a rough idea of how much rain to expect over the next 3 days including what has already fallen on Friday. It’s important to note that at first glance the numbers on the map may appear quite extreme as we usually see severe flooding with just 50-75mm from a thunderstorm let alone 100+mm. The thing to remember that all this rainfall will be spread out over 72 hours rather than just a few hours that we see with the major flooding events in the past.

Regardless, we haven’t really seen a lot of rain over the past few months so this will be a significant amount of rain for the ground to absorb and flooding will be quite likely to an extent. Since thunderstorms will be embedded within the precipitation over the next few days it will result in highly variable rainfall totals even within a small area. For example, one location may see 50mm while another gets 150mm. That’s why our forecast ranges are quite large since this event is very tricky to narrow down the exact amount of rain a location will see.