Mixed basket of fall weather in store for Southern Ontario
Expect frost for September, followed by a heat wave in October, before things cool down in November.

thestar.com
Aug. 18, 2014
By Paul Clarke

Early frost warnings and a late heat wave will make for fickle fall weather in Southern Ontario this year.

That’s the prediction of senior meteorologists from forecasting service Accuweather.com as the days become shorter and leaves begin to change colour.

The temperature in September is expected to be slightly cooler than normal with a risk of frost hitting areas north of Toronto before the month is over.

Despite the less-than-optimistic outlook, a late surge of warm weather in October, also known as an Indian summer, is expected to give Southern Ontario one last blast of summer before heading into what is expected to be a colder and wetter than normal November.

“It’s going to be an up-and-down fall across Southern Ontario,” said Brett Anderson, a senior meteorologist with Accuweather.com.

He said areas north of Toronto will likely see drier than normal conditions while the rest of Southern Ontario will see near normal levels of precipitation.

A weak El Nino system, which hasn’t been officially declared, is expected to create slightly colder than normal conditions for Ontario this winter, while Western Canada could see warmer than normal temperatures.

An El Nino is a band of warm water that periodically develops off the Pacific coast of South America. It happens irregularly and affects the jet stream that moves across North America. The last El Nino happened in the second half of 2009 and early 2010.

“With El Nino we typically see two jet streams,” Anderson said. “We have the polar jet, which has the colder air north of it which gets pushed further north, and then we have the subtropical jet, which has most of the storms and precipitation, and that actually gets stronger and moves further north.”

“When the two jet streams combine during an El Nino - look out - that’s when we get the big storms.”

British Columbia will likely be the hot spot this fall as ocean temperatures off the coast remain well above normal. This will likely keep coastal areas, such as Vancouver, warmer than normal, especially at night when temperatures usually drop, said Anderson.

Further to the east, Alberta and Saskatchewan will likely see near-normal temperatures with drier than normal conditions.

A small pocket of cold air will keep Manitoba and northwestern Ontario colder than normal throughout the fall, with early frost warnings expected.

Quebec can expect a drier fall with close to normal temperatures, with the exception of October, which is expected to be slightly warmer than normal.

In the Maritimes, the ocean’s temperatures will likely have a large impact on the region’s weather this fall. According to Anderson, ocean temperatures in Atlantic Canada are averaging three to four degrees warmer than usual, which will keep the region warmer than normal.

The warmer water may also increase the risk of storms in the region.

“The water temperatures, being as warm as they are, if there are any storms that threaten that area they could certainly remain stronger than they usually do,” he said, adding the official hurricane season isn’t over until the end of November.