Distant typhoon poised to bring snow to Canada this month
Wednesday, October 18, 2017, 4:36 PM - By definition fall is a season of transition in which we expect frequent pattern reversals with wild swings in temperatures.
However, the past five weeks have featured a rather persistent pattern, with only brief interruptions as warmer than normal temperatures have dominated across eastern Canada and colder than normal temperatures have been persistent across most of western Canada.
Be sure to watch the video that leads this article for further details on how a typhoon thousands of kilometres away can impact our weather here in Canada.
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However, a pattern reversal will occur next week with the coldest weather relative to normal aimed at the Great Lakes, right where it has been the warmest for the past month. While the upcoming weekend will feature late summer weather in the Great Lakes, lake effect rain and snow is expected before the following weekend.
This pattern change will be set in motion early next week as a deep trough in the jet stream digs into central Canada. This will open the door for a cold northwesterly flow out of the Arctic, sending temperatures below seasonal values. A second, re-enforcing shot of cold air will drive temperatures even lower late in the week and next weekend.
The dramatic swing in temperatures will be driven by an amplified jet stream – characterized by deep troughs and strong ridges – which is common enough in the transitional autumn season. However, this particular pattern change will be influenced by a major weather event on the other side of the world.
An intensifying typhoon, Typhoon Lan, will rapidly intensify over the next several days, potentially reaching Super Typhoon status (equivalent to a strong category 4 or 5 hurricane) before threatening the coast of Japan late this weekend.
Click play to watch below: Typhoon Track
While this powerful storm is thousands of kilometres away from Canada, it will have an impact on weather patterns across the Northern Hemisphere, including our upcoming pattern change.
Meteorologists use the term “teleconnection” for an atmospheric or oceanic feature in one part of the globe that has an effect somewhere else far away. A classic example of a more familiar teleconnection is the El Niño Southern Oscillation. This pattern, which relates to water temperatures and air pressure patterns in the equatorial Pacific, has a major and well-documented effect on North American weather. El Niño has been the driver behind some of our mildest winters in Canada, including 2015-16.
The tracks of western Pacific typhoons are a different type of teleconnection, and they can give us important clues about how weather patterns will change over North America during the following 6-10 days. Specifically, a recurving typhoon like Lan is often a sure sign of a deep trough developing over North America the next week.
This is not a direct cause-and-effect relationship – the typhoon doesn’t cause the North American trough, but there is a linkage. The typhoon pumps heat into the ridge commonly found to the northwest of Japan. This in turn causes a trough to dig in over the Bering Sea, which builds a ridge over the Gulf of Alaska and British Columbia. Finally, a trough begins to dig in over central Canada, paving the way for colder air to move south. You can think of it as a domino effect, or perhaps more precisely, like kids on a playground making waves in a jump rope. Although in this case the jump rope is the jet stream, and the kid tugging on the end is the typhoon.
This image below shows the forecast jet stream pattern over the North Pacific for next week. As you can see, the jump rope is making some wild swings, just as you would expect in the wake of a typhoon. A strong jet max is located northeast of Japan, and a powerful ridge over the North American coast is bookended by deep troughs on either side. This deep trough-ridge pattern will be the driver for next week’s pattern change.
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What makes this relationship particularly useful for forecasters, is that the track the typhoon takes can help us forecast the position of the trough in the jet stream 6-10 days later across North America. It tells us not only that there will be a trough, but where it is likely to be. If the typhoon tracks near or just east of Japan (as we expect with Lan), the trough is often found centred near the Great Lakes. A typhoon recurving further to west would suggest a trough over western or central North America, with ridging and warm weather developing in the east.
Each weather pattern is different, and the relationship between typhoons and troughs isn’t always perfect. But teleconnections are a valuable tool that forecasters use in long range and seasonal forecasts. They can help us make sense of model madness, and lend confidence to our ideas about upcoming pattern changes.