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Temporary heat in southern Ontario; Cooler pattern ahead

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Dr. Doug Gillham
Meteorologist, PhD

Monday, July 21, 2014, 10:15 AM - Across southern Ontario this summer we have seen several warm days, but we have not had an extended period of hot weather.

In fact, the temperature at Pearson airport has not yet reached 30ºC during the month of July. In the GTA, our average temperature for the month of July is running about a degree below the long term averages.

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Today and Tuesday will be very muggy, and Tuesday will bring our best chance of topping 30ºC across southern Ontario, though temperatures will be a few degrees cooler near Lake Ontario and Lake Erie.

However, after Tuesday there is very little heat in the long range forecast, and it is possible that we will not reach 30ºC again through early August.

A cold front will cross southern Ontario Wednesday morning and bring our best chance for widespread showers and thunderstorms during the morning, but this point, we do not expect severe weather with the front.

Thursday will be noticeably cooler and less humid, but not as cool as what we saw last week behind the front. Also, we will see a quick recovery back to near seasonal temperatures for Friday and the weekend.

At this point, Saturday looks great with sunshine and seasonal temperatures. However, we will have to keep an eye on the next approaching system as it possible that scattered showers and thunderstorms arrive as early as late Saturday or Saturday night. Sunday will bring a mixture of sun and clouds with scattered showers.

Looking further ahead to next week, it looks like will have a few days of unsettled weather at the start of the week as we transition into a pattern that will limit the hot weather to western Canada and Atlantic Canada with temperatures averaging below seasonal for Central Canada.

The image below shows a model forecast for the final five days of July. Regions with various shades of green are forecast to be 3 to 5 degrees C below seasonal while the various shades of blue indicate temperatures of 1 to 3 degrees C below seasonal. Southern Ontario, including the GTA are included in the region where temperatures are expected to be a couple degrees below what we typically see during late July.

However, while the map looks ominous (too reminiscent of the pattern that we saw last winter), we expect that most of the time the weather will be quite enjoyable. Our average high during this period is 27C, so this forecast indicates high temperatures will average out in the mid 20s.

It looks like this cooler than seasonal pattern will continue well into early August. The model forecast below is valid for the first ten days of August and fits well with our long range forecast.

This forecast does include the Civic Day long weekend, but it is too early to have high confidence in the weather details of those specific days. It certainly is possible to have a couple of days of warm weather in a pattern that is cool overall, so please check back for updates as the long weekend approaches.

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