Ontario falls back to seasonal reality with temperature drop, wet weather
A cold, upper-level trough will tumble into Ontario this week and stir up the atmosphere with thunderstorms, showers, lake-effect rain, possible waterspouts and even snow for northern portions of the province
Ontario likely saw its last 20°C of the year on Sunday as long-range models indicate a return to chillier, more seasonal conditions to finish October.
A more typical autumnal pattern has returned this week for about half of Canada’s population, including southern Ontario. In fact, chilly weather is anticipated for the Great Lakes region mid- and late week with bands of lake-effect rain, and maybe even waterspouts. Northern parts of Ontario could see some wet snow.
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The unsettled weather will include an intense band of heavy, lake-effect rain off Lake Erie, expected to reach into southern parts of the Niagara region, including Fort Erie and possibly into Niagara Falls. Localized rain totals could reach 50+mm, with the potential for thunder, hail, and graupel.
Tuesday:
The action begins on Tuesday as the surface low approaches.
An initial line of broken showers will lift from west to east as a subtle warm front sweeps through Tuesday morning. Showers will be heaviest through southwestern Ontario, weakening once it reaches the Greater Toronto Area (GTA).
Widely scattered, light shower activity may linger behind the warm front into the afternoon but a general pause in precipitation is expected until the evening or overnight period.
A surging cold front will spark a broken line of showers and/or thunderstorms as it punches into southern Ontario Tuesday evening. The line will track from west to east, beginning in Essex County around the dinner hour and arriving at the Highway 400 corridor around midnight when it will lose steam.
Watch out for strong wind gusts from 60-80 km/h that will accompany the rain and storms, especially along the immediate coastline of any water bodies.
Wednesday and beyond:
A potent pattern change begins. From Wednesday through the weekend, expect much chillier temperatures that will be a few degrees below seasonal.
Behind the cold front, chilly and brisk, westerly winds will move over the relatively warm waters of Lake Erie and Lake Huron. That will set the stage for respectable, lake-effect showers Tuesday night through Wednesday. Areas impacted will see prolonged periods of rain.
Bruce County will be the target for lake-effect rain off Lake Huron, possibly totalling 10-30 mm. However, 50+mm is possible for Norfolk, Haldimand County and Niagara because they will be under an intense, lake-effect rain band off of Lake Erie that may come with some lightning or hail due to its convective nature.
There is the potential for waterspouts, as well, due to a sharp contrast between lake surface temperatures and air temperatures aloft.
North of the Great Lakes, rain and snow-showers will be ongoing from Tuesday to late Friday across the districts of Kenora, Thunder Bay and Cochrane.
Snow accumulation will be slim to none thanks to marginal temperatures, which will hover around the freezing mark, and weak precipitation rates.