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Severe storm risk, abundant lightning for some in southern Ontario

Sunday, June 20th 2021, 8:23 pm - Some regions will see the week begin with unsettled weather, including lightning and rain, in southern Ontario.

Thunderstorms will track through southern Ontario into Monday morning and abundant lightning will be a noticeable aspect of the turbulent weather. There is even a slight chance of tornadoes in southwestern regions of the province late Sunday evening. The stormy weather will continue throughout the day on Monday and storms could be severe in parts of cottage country, eastern Ontario and southern Quebec. Details and timing, below.

Visit our Complete Guide to Summer 2021 for an in-depth look at the Summer Forecast, tips to plan for it and much more!

SUNDAY EVENING/MONDAY MORNING: SEVERE THUNDERSTORM RISK, ABUNDANT LIGHTNING FOR SOME

Stateside storms will track into southern Ontario late Sunday evening. The bulk of the storms and scattered showers should hold off until sundown. For the GTA, they aren't expected to roll through until midnight.

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Severe nocturnal storms are possible in the southwest region and significant amounts of lightning is expected. While the strongest storms are expected to remain stateside, some of them that cross the border may have the potential to produce a tornado in areas that are most likely to see severe weather.

Most storms will not reach severe criteria as they push further east through the Golden Horseshoe since the timing and dynamics are unfavourable. However, localized heavy rainfall and embedded thunder is likely.

These overnight thunderstorms will come in a few rounds and could continue into early Monday morning.

MONDAY AFTERNOON: COLD FRONT BRINGS HEAVY RAIN, SEVERE STORM RISK

There won't be a break from the stormy weather on Monday, as a cold front approaches southern Ontario in the afternoon. This will bring a line of thunderstorms to the region. Stronger storms are possible for portions of cottage country, eastern Ontario, and southern Quebec through the afternoon and early evening hours.

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Temperatures will still be very warm and humid weather ahead of the front, with daytime highs still sitting above normal.

Showers will linger into Tuesday for eastern Ontario. Totals will be highly variable across southern areas, but locally heavy rain is possible, especially in thunderstorms.

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Through Tuesday, an area stretching from Lake Huron shores to parts of cottage country may see 20-30 mm, with lesser amounts for the GTA, eastern and southwestern Ontario.

BEYOND: BRIEF COOLDOWN, THEN WARM-UP LATE WEEK

A shot of chilly weather is likely behind the system on Tuesday, thanks to strong northwesterly winds that will drop temperatures dramatically. A couple of days of below-seasonal temperatures is expected before warming up again later in the week.

Despite the warming trend, forecasters aren't expecting any consistent heat before the end of June, but hot weather may return in early July.

Stay tuned to The Weather Network for the latest updates.

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