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Ontario: Storm incoming for ontario, details here

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Friday, January 19, 2018, 8:00 PM - Another January thaw is spreading over southern Ontario, with above-zero temperatures set to last several days, followed by above-seasonal weather for much of the rest of the month, though there may be times where temperatures buck that pattern.

But don't let your guard down. A 'milder' pattern in the heart of winter can often, counter-intuitively, deliver some of our most impactful winter weather - and Monday will be no exception, with a storm glazing parts of Ontario with freezing rain and a heavy band snow.

Exactly what and where the impact of this storm will be will depend on the low's exact track (whether through the central or southern Great Lakes), and the strength of the Arctic high pressure over northern Ontario and Quebec (which determines how far south freezing rain can expand).

See below for what we know of this system's region-by-region breakdown, and two scenarios on how the forecast could firm up.

Keep on top of active weather by visiting the ALERTS page.

Weather Highlights

  • January thaw begins this weekend with temperatures near to above seasonal. Likely to last through first week of February.
  • Forecast challenge with Colorado Low on Monday, which brings two possible scenarios for weather impact to the province. 
  • Scenario 1 - Southern track is greater risk for southern Ontario with extended period of freezing rain for Greater Toronto Area. 
  • Scenario 2 - Northern track is greater risk for central and eastern Ontario to see prolonged freezing rain. Southern Ontario would see primarily rain with this track and northern Ontario would see significant snow. 

Region-by-region breakdown

GTA/Southwest: Above freezing temps hold on Sunday, with gusty winds particularly along the Lake Erie shores. Rain begins later Sunday, with 15-20 mm west of the GTA, 10-15 mm for GTA/Niagara, and up to 10 mm for areas further north. Monday sees a brief push of snow in the morning, switching to freezing rain for the morning commute, prolonged north of the 401 from Guelph through central Ontario. Lakeshores, Niagara and the rest of the southwest transition to straight rain, or start as rain, ending overnight.

Central Ontario: Initially snow Monday, 1-3 cm for Kawartha Lakes, 5-10 for higher elevations through Haliburton and Muskoka. Transition to ice pellets and freezing rain into the afternoon, freezing rain continues through the evening before a brief change back to snow and light flurries through Tuesday afternoon.

Nickel Belt: Sudbury and North Bay remain in the snow throughout the system, beginning later Monday morning and continuing through Wednesday evening. 20-25 cm expected for areas around lake Nipissing and Manitoulin Island back to Sault Ste. Marie.

Ottawa/Montreal: Morning commute looks clear, but snow spreads across lower Ottawa Valley for Monday afternoon. Risk for ice pellets and freezing rain looks to hold off until Monday night, diminishing by Tuesday morning for Ottawa and Montreal. 10 cm expected for Ottawa, 15-20 cm for Montreal. Flurries linger through Tuesday.

WATCH BELOW: Hour-by-hour precipitation type

As mentioned, freezing rain extent and duration will depend somewhat on which track the storm is likely to take. Below are two scenarios we are looking at.

Scenario 1 - The Southern Track

You can think of the 'southern track' as a higher risk for southern Ontario. With the storm forecast to cut across southwestern Ontario, this would set up an extended period of freezing rain from the GTA throughout much of southern and central Ontario on Monday, with a change to rain possible from the southwest into the GTA Monday evening and overnight.

On the colder side of the storm, eastern Ontario, the Ottawa Valley and the Nickel Belt would be on the line for heavy snowfall developing Monday night into Tuesday, with substantial totals.

This far south of a track would leave most of northern Ontario (apart from the Nickel Belt) out from the threat.

Scenario 2 - The Northern Track

A northern shift in the track through the central Great Lakes would leave most of southern Ontario with a brief risk of freezing rain on Monday before the warm air takes over and it changes over to rain. In eastern and central Ontario, this would now turn into a more prolonged freezing rain event beginning late Monday, with a brief change over to rain Monday overnight.

Now you can think of the 'northern track' as a higher risk for northern Ontario, as they would then be added into the threat for significant snow.

Behind the storm, blustery winds develop on Tuesday, but temperatures will still be relatively mild (for January standards). Near seasonal conditions Wednesday and Thursday before much milder weather arrives for late next week and weekend.

The main takeaway from discussing the possible scenarios is to give you the knowledge and a heads up that a storm is ahead, but the details of the impacts are still being fine-tuned. Be sure to check back throughout the weekend for updates.

With files from Erin Wenckstern.

WATCH: Why ski resorts actually LIKE the annual ‘January thaw’

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