Colorado Rain: It Doesn't Have to Be a Butterfly

How does Arctic ice contribute to torrential rains and killing floods in Colorado?

Prospects for a climate crisis made climate science prominent.  As it turns out, it is the most comprehensive set of scientific methodologies and disciplines attempted so far.  It involves fairly elementary physics and chemistry, but also very sophisticated ideas and techniques.  The behavior of clouds, of air currents, the oceans (temperature, depths, interaction with carbon, etc.) are very complicated scientific (and mathematical) problems.  Chaos theory is only a generation or so old, and it is crucial to all this.  There are even newer constructs trying to find the keys to complexities.

At both the theoretical and practical levels, the physical sciences that bear on climate and the effects of the climate crisis are robust.  They are impressively prepared, though crucial gaps remain.  They are making real progress on clean energy, including low cost and relatively low tech forms.  There are some good ideas for dealing with carbon, and some very big, very bad ones.  In tragic contrast, our political behavior is barbaric.

The complexities of climate are better understood now, though explaining those very complexities invites skepticism that's easy for know-nothings to exploit.  But for those who really want to understand what might be going on, there are at least tentative explanations.

So what about the droughts, fires and especially the rains that came to Colorado?  In an NPR interview, Rutgers researcher Jennifer Francis first described what was different about the Colorado rains:

For one thing, the floods that they usually have this time of year are typically more of the flash flood variety, whereas the one that occurred last week was a very long lived event for Colorado. It spanned a few days. Normally, they just come and go. And the amounts of rain are just really staggering. I mean, usually, in the month of September, say, Boulder, Colorado, would typically get about two inches. They got nine inches in just one day. And over the whole week, it added up to about 17 inches. And this can be understood in the perspective of their typical amount of rain they get for the whole year, which is only 20 inches.

Then what was different about the weather patterns that led to the floods:

There was a large swing in the jet stream northward up over the whole western half of North America. So there was this big swing northward in the jet stream and then, south of that, was what we call an upper level low. So the jet stream was bringing in moisture from the Pacific while the lower level winds were actually from the southeast bringing moisture in from the Gulf of Mexico.

And so we had moisture at two levels in the atmosphere, which made for a very, very large amount of water vapor available. So as that wind came in from the southeast at low levels, it hit the Rocky Mountains, was lifted by the mountains so it then cools and condenses and it wrings that moisture right out.

And because there was this large swing in the jet stream and this upper level low, this configuration we call a blocking pattern. And it's called the blocking pattern for the very good reason that it means that the weather patterns are stuck. The block means that it's blocking things from changing. And so we were in this pattern for several days and we've been seeing these sorts of blocking patterns quite a lot in the last couple years."

Blocking patterns occur naturally but Francis said the reasons we're see more of them and are likely to keep seeing them in the future has to do with Arctic ice.  The first is related to the years of drought in the West:

But in the summertime and in this period of years that we're in right now in particular, we've had a prolonged drought in the western half of North America. And we think this is at least partly related to the fact that, of course, sea ice is disappearing, the Arctic is warming very rapidly, we're losing the snow cover much earlier on high latitude land areas, so in the far northern part of North America, and this causes the soil underneath to be able to dry out and warm up much faster in the spring, which kind of gives a jumpstart to the warming season of summer.

So we think this might be contributing to the jet stream taking these very large northward swings because that soil, once it dries out, is able to heat up much more and it kind of creates a bulge or a dome of hot air. And this sort of contributes to the jet stream taking these sorts of patterns."

The effect of less Arctic sea ice is a change in the behavior of the jet stream.

"...because the Arctic is warming much faster than the areas farther south and it's that temperature difference between the Arctic and areas farther south that really is what drives the west to east winds in the jet stream. So we are, in fact, seeing those west to east winds of the jet stream slowing down and we believe it's related to this differential warming of the Arctic.

And once the jet stream does slow down, it tends to take a wavier path as it goes around the Northern Hemisphere so bigger swings to the north and south, which, you know, we're starting to see that happening more."

Francis added that scientists are intently studying this new behavior for clues to future weather, because the jet stream often determines it for a given area.  It was a factor, she says, in the path of the destructive hurricane Sandy on the U.S. East Coast.

And it's those waves in the jet stream that create the weather that we feel down here on the surface. So where you're located relative to different parts of these waves determines what kind of weather you're in. But what we are seeing is an increasing frequency of these northward bulges, which we call ridges, occurring in the North Atlantic, in particular.

You can think about Sandy, for example, when Sandy came along, there was one of these very strong ridges or blocking patterns in the North Atlantic and that's what helped steer her into the East Coast. And we also see them becoming more frequent in the western U.S. and other areas as well. So it does seem that we're starting to see some patterns emerge that will help us make longer term predictions in the future."