Frost/freeze for parts of the East tonight
A large, dome of high pressure will build over Ontario later tonight. Under clear skies, light winds and the dry air mass, temperatures will drop steadily overnight with areas of frost/freeze by early Tuesday morning in the normally colder locations away from cities and large bodies of water.
Below are the average dates for the first frost in selected cities, courtesy of Veseys. If you live in a rural location not too far from one of the selected sites below, you can expect that date to be anywhere from 5 to 15 days earlier on average.
Windsor, Ont. ... Oct. 22
Toronto, Ont. ... Oct. 6
Sudbury, Ont. ... Sept. 25
Peterborugh, Ont. ... Sept. 20
Owen Sound, Ont. ... Oct. 15
London, Ont. ... Oct. 8
Kingston, Ont. ... Oct. 10
Barrie, Ont. ... Sept. 16
Hamilton, Ont. ... Oct. 15
Ottawa, Ont. ... Oct. 5
Montreal, Que. ... Oct. 7
Sherbrooke, Que. ... Sept. 10
Trois-Rivieres, Que. ... Sept. 23
Quebec, Que. ... Sept. 29
Baie Comeau, Que. ... Sept. 15
Front likely to bring thunderstorms later in the week
A fairly vigorous cold front will draw warmer, more humid air northward as it tracks eastward late in the week, and this could lead to a widespread area of showers and locally strong thunderstorms.
The map that we drew below shows the general timing for the threat of strong thunderstorms later this week.
Keep in mind, the overall threat of severe thunderstorms is on the wane during September as the solar heating is diminished and thus the amount of instability is diminished. However, if there is a fairly strong jet stream with clashing air masses it can easily overcome the September sun effect and lead to severe weather.
Possible tropical threat for Atlantic Canada early next week
Some computer models show low pressure organizing somewhere southeast of Bermuda this weekend and possibly a tropical storm. The modeling tries to draw the system northward between an approaching trough and the north Atlantic high later in the weekend and early next week with a potential direct impact on Newfoundland around next Monday.
Still very early and things can and will change over the next few days. Just wanted to bring that to your attention. I will monitor the situation through the weekend.
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