'Weather bomb' for the Bering Strait? Snow for the Prairies and Ontario? Blame Typhoon Nuri!
Tuesday, November 11, 2014, 11:19 AM - We've all heard of the so-called butterfly effect, but what happens when something much, much bigger than a butterfly 'flaps its wings' on the other side of the world? Watch Dr. Doug Gillham and Jaclyn Whittal discuss these kinds of teleconnections above, then check out the details below.
Typhoon Nuri has already racked up an impressive record, as it tied with Typhoon Vongfong over the weekend for the strongest tropical cyclone so far this season - peaking as a Category 5 Super Typhoon. However, even now, as the storm moves away from Japan, it doesn't look like it's quite done yet. Over the next couple of days, it's going to transition from a warm-core tropical typhoon into a cold-core extratropical storm. As it does, it will intensify and drive up into the Bering Strait, influencing weather patterns thousands of kilometres away as a result.
Here's a look at the atmosphere over the North Pacific Ocean, at the level of the jet stream, roughly 10 kilometres above the ground.
If it's difficult to orient yourself on the map, Asia is along the left edge of the image, with the islands of Japan just to the lower left of the swath of red in the first panel. North America is on the right, and the Bering Strait is just to the upper right of centre.
The concentric lines are contour lines, like on a terrain map, but here they're in 10s of metres above sea level. The colours are wind speeds, in knots (double the value for knots and that's a very rough estimate of kph), and barbed arrows are the actual wind speed and direction. Note that the colours also denote wind speeds, to make the patterns more obvious, and show off the jet stream pattern nicely.
Technically, you can't actually see Nuri on the map to start, but it's roughly located underneath the western edge of the bright red patch in the first frame of the animation. As time progresses, and Nuri deepens into what's known as a 'weather bomb' as it tracks to the northeast, you can see it 'poke' up to this level, starting around the 3rd frame (18 hr), and by the 5th frame (24 hr) it has formed a tight patch of concentric circles to the north of the main flow of the jet stream.
After that, watch how Nuri influences the jet stream, especially towards the right side of the map. From its position in the Bering Strait, it digs a deep, widening trough to the south of Alaska, while dragging the flow downstream from there far to the north, over Alaska and the Canadian north.
DID YOU KNOW?: A weather 'bomb' is a low pressure centre that drops by at least 24 millibars in the span of 24 hours.
All this is happening in fairly close proximity to Nuri (globally speaking), but let's see what happens further east as a result. The animation below is on the same timeline as the one above, but with the view shifted over North America.
Just as Jaclyn and Dr. Doug discussed in the video, the area downstream of that jet stream ridge over the Pacific coast is what we're particularly interested in. Watch above as Nuri digs that trough south of Alaska and forces the ridge up to the north. As that ridge forms, it results in a deepening trough over the rest of Canada.
Where's the influence from Nuri in all this?
As Nuri churned its way up towards the Bering Straight, and deepened into the weather bomb, it started adding energy to the jet stream flow, mainly in the form of 'shortwaves' - small ripples in the flow. They may not look like much, but these ripples can have a strong influence on the larger-scale flow - weakening ridges and digging deeper troughs. One good example in the first animation is along the southeast edge of Nuri, when it's in the Bering Straight. A series of these small ripples end up digging a trough there until the main low pressure centre slips down into it.
There are plenty of these ripples visible in the flow in the second animation, especially along the contours through the Prairies. They are quite small, but since there are so many of them, they really start to add up, digging a few troughs that sweep down through the US Midwest and off to the east coast.
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However, as Nuri exerts its influence over the Pacific, (to the upper left in the animation above), it pushes a weaker trough that's just ahead of it from south of Alaska, up over the Rockies and then down into the Prairies. This weaker trough, now acting as a strong shortwave in the flow, digs out a wide trough that stretches from southern Alberta to the island of Newfoundland, and as Nuri builds that tall ridge over the Pacific Coast, it spawns more shortwaves that dig the trough out a bit more while dragging down a significant chunk of cold Arctic air down to fill it in.
What's that going to mean? Very likely strong winds blasting across a wide stretch of the country, and significant snowfall for some areas - especially in southern Alberta and southwestern Saskatchewan on Sunday, and then northern Ontario for Wednesday, which may touch off a 'multi-day' lake effect snow event in southern Ontario.