Fall 2021 outlook for Canada

La Nina conditions are anticipated this fall, which will likely play a key role in the average weather conditions across portions of Canada during this upcoming season and even perhaps into the upcoming winter. La Nina is the abnormal cooling of the surface waters of the Pacific Ocean near the equator, which can influence the strength and position of the jet stream across North America. 

In addition to La Nina, water temperatures farther north in the Pacific, including the North Atlantic and the Great Lakes, may have some influence on local weather conditions for meteorological fall 2021 (September, October and November).

With a strengthening La Nina, the strongest influence will be along the Pacific coast this upcoming season. La Nina tends to favor a stronger, Pacific jet stream that is more directed into the United States Pacific Northwest and southern British Columbia. The jet stream is like a pathway for storms, thus we are expecting a stormier fall, especially across the western half of British Columbia, with above-normal rainfall. Large portions of British Columbia have been under severe drought and dealing with a tremendous amount of fires and poor air quality this summer. The good news is that this pattern will likely deliver some much needed rainfall, higher humidity, improved air quality (better dispersion of smoke) and of course lower temperatures. The bad news is that in areas where there will be less rain, such as south-central British Columbia, there will be more wind, which may inhibit firefighting efforts. In burn scar areas along hill and mountain slopes, any rain storms may lead to debris flows.

The projected stormier pattern may get the snow season off to an early start in the Coastal Mountains of British Columbia and farther east into the Rockies of British Columbia and Alberta. 

Parts of northwestern British Columbia and the Yukon may end up with a colder fall compared to normal as a majority of cold outbreaks may be directed into this region from eastern Alaska. 

A majority of storms are expected to turn northeastward into the northern Prairies, which may prevent much of the early-season cold from getting down into the southern Plains. This type of storm track will also mean a windier- and drier-than-normal pattern for much of the southern Prairies, which has been hit hard by drought this spring and summer. 

Much of eastern Canada is expected to have a mild fall, but there may be late-season cold shots that may be directed into Ontario and northern Quebec. 

Above-normal water temperatures throughout the Great Lakes will likely persist through the season, which will have its biggest influence on nighttime temperatures (being milder) across the region. 

Severe thunderstorm season may also be prolonged a bit across Ontario and Quebec and linger into September. 

Farther east, the combination of abnormally warm sea surface temperatures in the northwestern Atlantic Ocean combined with an active storm track near the region will favor above-normal temperatures. 

There is a higher-than-normal risk for a landfalling tropical storm or hurricane over Nova Scotia this fall as the Atlantic basin is expected to have a higher-than-normal number of storms that may recurve northward toward the region. Warmer water than usual may also allow some storms to maintain strength longer than usual as they get this far north.

In terms of Henri, it looks like Henri will rapidly weaken as it moves inland across southern new England on Sunday and barely have any tropical characteristics by the time it approaches Nova Scotia early next week. I expect few, if any, notable impacts for Nova Scotia and New Brunswick.

Of course, we must continue to factor climate change into these outlooks as odds further tilt more and more toward more widespread, seasonal warmth versus cold, especially from the northern mid-latitudes and up into the Arctic region. Yes, there can still be some seasons of widespread cold, but those are becoming more infrequent.