The official start of the fall season has brought some of the rainiest days seen all year, courtesy of a pair of systems teaming up to bring a long-duration rainfall event. It began Wednesday, and by the end of Thursday, some areas will be drenched by more than 100 mm of rain – rising fears of localized flooding, with the ground simply too waterlogged to absorb it all. Motorists should be mindful of the conditions when heading out on the roads Thursday. More on what remains, below.
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INTO THURSDAY: MORE RAIN SWEEPS THE PROVINCE
Wednesday was likely the rainiest day of the year so far for many communities across southern Ontario. In fact, for some, there's a non-zero chance that they may end up blowing away their monthly averages for September, depending on how the rest of the system's effects shake out overnight into Thursday morning.
So far, the totals are hefty, with many communities easily crossing the 50 mm mark by the early evening, after the day's many drizzles and downpours as the cold front marched through.
The system has so far been accompanied by some stiff winds here and there, knocking down tree branches. In the early part of the day, power outages exceeded 20,000 among Hydro One customers, fluctuating through the afternoon and early evening. By 7 p.m., some 8,000 customers were without power.
A second moisture-laden system began trekking into the southwest Wednesday afternoon, making for a rainy night for areas that already would be thoroughly drenched – and, for areas along riverbanks, a new problem, depending on how much falls.
THURSDAY: AFTER EXTREME TOTALS, RISING FLOOD RISK A CONCERN
The rain continues through Thursday for many locations, and the last drops by only stop in eastern Ontario early Friday.
Locally, some areas could be on the hook for totals surpassing 100 mm of rainfall, especially where embedded thunderstorms occur – in some cases blowing away the meagre season-long totals of the only just-ended summer.
So much rain will have fallen by the end of this event that the ground is going to be thoroughly waterlogged. With no ability to absorb extreme totals, the rain will runoff into low-lying areas and rivers, leading to localized flooding.
The Toronto and Region Conservation Authority issued a flood watch early Wednesday evening, and other conservation authorities are likely to follow suit.
"Please exercise extreme caution around all bodies of water and avoid driving on flooded roadways or in low-lying areas and underpasses. Be alert for possible transportation delays and road closures. Stay safe," the TRCA said in a statement.
Motorists should be cautious largely because the downpours will make for poor visibility and lead to ponding on the roads, along with some flash flooding on roads in low-lying areas.
"If visibility is reduced while driving, turn on your lights and maintain a safe following distance. Localized flooding in low-lying areas is possible."
LATE WEEK: COOLER WEATHER MARKS FIRST DAYS OF FALL
There may be some spotty showers lingering Thursday night and into the pre-dawn hours Friday morning before the system pulls away from the region, making for a fair day afterwards.
Temperatures will tumble to more seasonal values behind the systems, remaining cooler through the weekend.
Another system will track into southern Ontario on Saturday with rain reaching the GTA during the afternoon. Rain will spread into eastern Ontario in the evening and overnight. However, some sunshine returns to southern Ontario for Sunday.
Seasonably cool conditions will dominate for next week, but still within a few degrees of seasonal. A warmer pattern (relative to normal) should return during the first week of October, but of course "seasonal" continues to steadily fall through these next months.
Be sure to check back for the latest updates on this slow-moving system that kicks off the fall season in Ontario.