October is dressing up as July for Halloween as an unusual bout of mid-autumn warmth heads for southern Ontario.
Some communities could wake up Thursday morning to temperatures warmer than you’d typically see during an average morning in the middle of the summer.
The warmth won’t last long, though. A big change is on the way to close out the month.
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Extremely unusual temperatures for late October
North America is split in two this week. We’re going to start the week with a big upper-level trough over western portions of the U.S. and Canada while a significant ridge of high pressure moves east over the Great Lakes.
This ridge will keep conditions unseasonably warm across southern Ontario through the beginning of the week. While ridges tend to bring above-seasonal temperatures to communities under their influence, it takes more oomph in the atmosphere to foster exceptional warmth.
We’ll watch a Colorado low develop and move northeast through the middle of the week, bringing unsettled weather to the eastern Prairies and northern Ontario by Wednesday.
Midsummer warmth in time for Halloween
The ridge of high pressure over the eastern United States will combine forces with that Colorado low to push southerly winds over southern Ontario, helping to enhance those remarkably warm overnight temperatures late Wednesday into Thursday morning.
But first, here’s a look at average overnight lows during the month of July.
July’s average overnight temperatures hover around 16.6°C in Toronto and about a degree cooler down toward Hamilton and London. A typical July low would come in around 18°C in the usual hotspot of Windsor.
Why does that matter? Well, take a look at what we’re expecting across southern Ontario by Wednesday night.
This is some remarkable nighttime warmth for this late in the season.
Forecasters are expecting Wednesday night’s lows to bottom-out around 17°C across the board in Toronto, Hamilton, London, and even up the road in Barrie. Windsor might only hit 19°C by Thursday morning. These readings would all comfortably beat the previous records for the warmest temperature we’ve seen so late in the year.
It’s not just southern Ontario getting in on the midsummer warmth. July-like lows are expected Wednesday night as far north as Sudbury and Sault Ste. Marie.
Our sudden spell of summer-esque warmth won’t last long at all. A push of cooler air moving in behind that Colorado low will send things crashing back to reality for the end of the week.
Expect a comparatively chilly few days to kick off the beginning of November, with a return to above-seasonal temperatures likely soon after.