Dramatic temperature drop after spring-like warmth, thunderstorm risk in Ontario

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From record-breaking spring-like warmth and thunderstorms, to a fast and steady temperature drop and the threat of a flash freeze -- the weather across southern Ontario this week will certainly have it all.

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The thunderstorm threat creeps into the region on Tuesday, as temperatures soar well above seasonal once again, with the risk for periods of heavy rain and even small hail. Some potent storm cells may bubble up in the southwest, which is certainly an uncommon feature for the month of February.

A drastic temperature change will soon put an end to the warmth, bringing with it the chance of a flash and hard freeze, depending on the locale, with values plummeting by as much as 20 degrees in a short amount of time. To add to that, a round of snow will follow suit for some.

Drivers are being urged to plan ahead, and to adapt to the rapidly changing conditions.

_Tuesday: More spring-like warmth with the threat for thunderstorms

After a warm and above seasonal Monday, temperatures increase further on Tuesday across all of southern and eastern Ontario. However, locations downwind of the lakes will stay much cooler, while inland communities will enjoy readings well into the mid-teens.

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Communities along Highway 401 like Brockville and Cornwall could see readings as high as 17°C on Tuesday as warmer winds blow out of New York, a tally that is about 17 degrees above normal for the end of February. Warm winds from across the border could bring similar temperatures to the eastern Niagara Peninsula.

The all-time February temperature record for Ottawa is 12.4°C, set back on February 27, 2000. As it stands, this likely will be broken this week.

With the spring-like warmth comes our first risk for thunderstorms, as a warm front pulls some instability across southern Ontario on Tuesday. Thunderstorms were reported in the Bruce Peninsula early in the day, with the risk continuing across the south and up towards cottage country by the early afternoon hours.

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After the lunch hour, the risk spread across the Greater Toronto Area (GTA), as the warm front lifts across the area. Keep an eye out for a passing heavy shower, rumbles of thunder, and even the risk for small hail, across the south.

A second round of storms will need to be monitored closely late Tuesday and into Wednesday.

While the general nature of the storms will remain non-severe, the extreme southwest has a window of opportunity for more potent cells to develop. Good dynamics ahead of the cold front is what could fuel the strong storms, with the risk for larger hail and powerful wind gusts.

At this time, these dynamics are more likely to stay stateside due to the timing of the front through the overnight hours. Forecasters will be keeping a close eye on the timing and if it speeds up, as the chances for stronger storms then increases.

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Wednesday: Major cooldown with the threat for snow and a flash or hard freeze

Wednesday is when things take a tumble, and fast, too.

The region will see a cold front push in, with a razor-thin line separating a snowstorm in the north and another potentially record-breaking warm, stormy day in the south.

On Wednesday morning, the GTA and eastern Ontario will likely see heavy rainfall to start the day, with possible rumbles in the air, too.

By Wednesday afternoon, conditions will begin to change in a hurry. Most may record a 20-degree drop in temperatures by the overnight, making it one of the more extreme temperature drops in recent memory.

Forecasters are concerned for a flash-freeze event with any standing water turning to ice. Central and eastern Ontario could see a temperature drop of 10 to 15 degrees within a three to four hour period Wednesday evening. That will result in surfaces becoming slipper rather quickly. Any plans to travel during this time will likely need to be postponed.

Meanwhile, parts of the southwestern sections could see a hard freeze.

Ottawa’s high of 14°C during the day Wednesday will turn on its head to a brutal low of -13°C by the overnight period.

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In addition, temperature swings such as these will come in with a roar. Gusty winds between 60-80 km/h are a concern across southern and eastern Ontario Wednesday evening, with bitterly cold wind chill values present.

After temperatures plunge, precipitation will rapidly transition to snow across southern Ontario Wednesday overnight into Thursday.

Precipitation will quickly change over to bursts of snow, including a super snow squall off of Lake Superior, stretching deep into New York. Travel will be near impossible within the snow squall, with 60+ km/h winds and snowfall rates near 3 cm/h.

A narrow band of intense winter weather will cause havoc on the roads Thursday morning for the Bruce Peninsula, Barrie region, sections of the 400 and 401 east of Toronto. Drivers are urged to consider postponing travel during this time.

The good news is that the burst of cold won’t last for long. Temperatures will quickly rebound across southern and eastern Ontario heading into the weekend.

Stay with The Weather Network for all the latest on your forecast across Ontario.

WATCH: What is a flash freeze, and why is it so dangerous?

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