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ONTARIO | Changeable pattern

Ontario: WILD temperature swing and weekend storm risk


Digital writers
theweathernetwork.com

Thursday, October 4, 2018, 7:10 PM - Get ready. This roller coaster is a wild one as temperatures take a quick and steady tumble before another significant weekend warm up. A rain and thunderstorm risk also looms for the Thanksgiving weekend. More on this, below.

(A look at the next three months: Your Official 2018 Fall Forecast)


WEATHER HIGHLIGHTS:


THE AIR MASS BATTLE IS A VIGOROUS ONE

Fall is very much a transitional season, and the first week of October has certainly been living up to that reputation across Ontario as we play host to a slow-to-move boundary that has seen storm after storm track through the region, bringing alternating bouts of chilly rain and pleasant fall warmth.

CLICK TO PLAY: STORM DETECTION THROUGH THE WEEKEND


After a brief break from the two doses of rain earlier this week, a stronger system targeted northern Ontario with heavy rain and damaging winds late Wednesday and into early Thursday.  According to Environment Canada, a gust over 90 km/h was recorded at Sault Ste. Marie's airport at 4 am Thursday. 

"These winds may produce local power outages, especially with the ground being saturated," EC warned, adding that the gusty northwest winds will gradually diminish to 70 km/h by mid-morning.

Hydro One said more than 24,000 customers were already without power by Thursday morning with some northern Ontarians reporting "branches and trees down everywhere." 



WARMER PATTERN RETURNS FOR THANKSGIVING WEEKEND (BUT WITH A STORM THREAT)

Daytime highs will remain several degrees cooler than seasonal for Friday with a brisk east wind off Lake Ontario ahead of another fall storm tracking into northern Ontario on Saturday. A tight temperature gradient will remain over the province this weekend, with below seasonal air dominating the north and above seasonal and even muggy weather in the south. Periods of showers and embedded thunderstorms can be expected across the province, hindering the full warm up potential. 

Storm Risk Breakdown:

Saturday will have a low-pressure system track through southern Ontario and the Great Lakes Basin. With this system will bring with it a warm, humid, and unstable airmass but there will still be a relatively tight gradient along the warm front. 

The placement of this warm front is key as to where a thunderstorm risk will develop. For now, latest guidance indicated that the warm front is expected to clear southwestern Ontario and setup either through or just north and east of the GTA -- meaning that the more unstable airmass could setup across southwestern Ontario, the GTA, as well as Hamilton and Niagara.

Through the mid to late afternoon the cold front associated with the low is expected to cut through the unstable air leading to the threat of thunderstorms mainly for the region mentioned above. With the current trend, sufficient instability and wind shear are expected to be in place Saturday afternoon to lead to the develop of vigorous thunderstorms and perhaps even a few severe storms, with the main threats being strong winds, small hail, and heavy rain.

The main caveats to this setup are that if the warm front does not push into southern Ontario, then the storm threat will be rather limited to nil. The other caveat is if any morning cloud cover will clear out enough to allow for enough daytime eating to build up the instability. Stay tuned for updates as we continue to monitor this evolving forecast.

The Temperature Swings:

"Sunday will be several degrees cooler than Saturday, but still warmer than seasonal," Gillham adds. We will have the threat for showers, but most of the day will be dry."

By Thanksgiving Monday, temperatures may soar above the 20°C mark in southern Ontario, but there is uncertainty as to where the dividing line will be between the summer weather to the south and cooler weather to the north. 

CLICK TO PLAY: FLUCTUATING TEMPERATURE GRADIENT THIS WEEKEND


"It is possible that the wind will remain off of Lake Ontario for most of the day keeping temperatures several degrees cooler across most of the GTA," says Gillham. "While Niagara has the potential to climb into the mid/upper 20s, we may need to drop our forecast temperatures for the GTA back into the upper teens."

By Tuesday, confidence is much higher for the summer-like weather with all time humidex records in jeopardy. High temperatures are expected to reach the mid to upper 20s feeling closer to the mid 30s with the humidity. 

A very warm pattern is expected for most of next week in the south, leaving the province divided and with an active storm track still in full effect. Some communities, potentially including northwestern Ontario, may be preparing for a potential blizzard as the south bakes in late-summer heat.

"The unusually strong Bermuda High will likely still fight back at times during the second half of October with the potential for brief periods of warmer weather, but the shots of colder weather, which have been focused across the Prairies for the past month are expected to start having more impact on the Great Lakes region," warns Gillham. 

WATCH BELOW: DOES TEMPERATURE CHANGE ALONE LEAD TO SICKNESS?


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