Pattern change: Looking to the end of August
Wednesday, August 20, 2014, 10:19 AM - So far, August has featured above seasonal temperatures for most of western Canada and parts of Atlantic Canada. Below seasonal temperatures have been found over parts of central Canada, especially across Ontario.
The map below illustrates the pattern that we have seen through August 18, 2014. The various shades of orange and red highlight the regions that have seen above seasonal temperatures while the various shades of blue and green show the below seasonal temperatures which have been most pronounced around the Great Lakes. Most of the United States has also been cooler than average this month so far.
However, in many areas the temperature trend for the month has been overwhelmed by the pattern that we have seen during just the past week. The map below shows temperatures relative to local averages over the past seven days. Most of Ontario was near seasonal until several days of October-like weather arrived for the bottom half of last week. Meanwhile, heat was the story across parts of the Prairies and British Columbia.
So where do we go from here for the final third August?
A significant pattern change is occurring which will bring the coldest weather in the country to places that have been warm so far this month.
The model forecast shown below illustrates this pattern change as it shows temperatures relative to seasonal that are forecast from Thursday, August 21 through Monday, August 25.
The various shades of green across the Prairies represent temperatures that are forecast to be 3 to 7 degrees Celsius below seasonal during that period as high temperatures only reach the mid to upper teens.
Southern and central Ontario will get see a break from the autumn-like weather, but most areas will not see true summer heat. The increasing humidity will make it feel muggier and keep overnight from dropping off, but clouds and scattered showers and thunderstorms will also limit how warm it can get during the day.
The pattern is less defined across Atlantic Canada, but as we head towards the final days of the month it looks like temperatures will trend towards above seasonal to end the month. The map below shows a model forecast that for August 26-31 and the shades of orange represent warmer than average temperatures as we head into the Labour Day long weekend.
The autumnal weather pattern should ease somewhat for at least part of this period across the Prairies, but overall the cool pattern is forecast to persist.
The pattern for next week across Ontario, especially southern and eastern Ontario, is more difficult.
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There is considerable uncertainty as to how quickly the cool weather will spread east. While the above model shows temperatures averaging below seasonal next week, it looks like the week could feature a temperature roller coaster with a couple of warm days mixed in rather than a persistently cool pattern. However, it appears that temperatures will eventually trend back to below seasonal as we head into the Labour Day weekend.
Meanwhile, a warm ending to August is expected for much of British Columbia.