It’s certainly hot in the southwestern USA at the moment — a dome of heat has established itself under a persistent high pressure ridge, and temperatures are pushing up towards all-time highs. Wildfires are running out of control. One caused the tragic death of 19 firefighters at Yarnell Hill in Arizona yesterday. One more extreme weather event to add to this year’s growing list, and as with most of the others, there’s a clear sign of a link with rapid climate change. That heat dome is being held in place by a large, slow-moving northward loop in the jetstream — and that jetstream pattern is beginning to look very much like the characteristic fingerprint of rapid warming in the northern hemisphere, as Jennifer Francis explains in this video, recorded at a Climate Desk event in Washington last month. It’s just about the clearest explanation of what’s going on that I’ve encountered — particularly in her description of why the jetstream exists in the first place, and why warming is changing the way it behaves. If you want to understand what’s going on, you have to watch this.
There’s a full recording of the Climate Desk event here, including a talk by Weather Channel meteorologist Stu Ostro. Ostro used to be a confirmed sceptic, but began to see changes in weather patterns that he traced back to the effects of warming — specifically, an increase in the “thickness” of the atmosphere, the very thing that’s driving the changes in jetstream behaviour.
Could this heatwave be the same one that was hitting Alaska a short time ago?
I’m not sure how the synoptics evolved, Noel, but it’s a possibility that a big loop in the jetstream has moved slowly eastwards – that would be the normal progression. But it’s also possible that one loop collapsed, to be replaced by another further east. Interestingly, Calgary — still suffering from the aftermath of its big flood event — is also heading for potentially record-breaking heat in this event.
Looks like a different loop, although their formation so close together in time and space may not be entirely coincidental. Here’s a useful link for tracking the jets: http://squall.sfsu.edu/crws/jetstream.html. The polar view animation is best for getting an overall sense of things.
See also http://www.popularmechanics.com/science/environment/climate-change/how-the-dual-jet-stream-sparks-this-weird-summer-weather-15634917#ixzz2XRu4pxGC, although I’m not quite sure what it means.
As you say the polar views are the most interesting but I would need a course on reading them or a lot more info on presures and temperatures. I could not get anims to run past June 30. However, I suspect the answer to my original question is no.
Jeff Masters wunderblog makes it clear that the Alaskan heatwave is separate to the one bedevilling west USA.
Third extreme jet stream pattern of the past five weeks
This week’s extreme jet stream pattern is the third time in the past five weeks that we’ve seen a highly amplified ridge-trough pattern that has led to extreme weather. The others:
1) The end of May and beginning of June, when the $22 billion Central European floods occurred. A high pressure ridge became stuck over northern Scandanavia, causing all-time May heat records–as high as 87°F–at stations north of the Arctic Circle in Finland. The high pressure ridge blocked low pressure systems from moving north, and a series of two low pressure systems dumped record rains over Austria and Germany, creating the highest floods ever seen on portions of the Danube River. The $22 billion price tag made it the 5th most expensive non-U.S. weather-related disaster in world history.
2) June 18 – 22, when a ridge of high pressure over Alaska broke all-time heat records in the state, with unofficial readings as high as 98°F. A low pressure system became trapped over Alberta, Canada, bringing the city of Calgary a $3 billion flood disaster. This was the most expensive flood in Canadian history, and third most expensive natural disaster of any kind for the country. The only more expensive disasters were a 1989 wildfire ($4.2 billion) and a 1977 drought ($3 billion.)