There is a nice piece of map study waiting for us today. I am going to turn it into a challenge that will make it kind of fun for anyone who has gotten familiar with how these relationships work and may thus have good ideas about what to expect. I’ve cheated a little this time, but have also begun to realize the potential for making solid predictions from a limited amount of information. This is a fairly simple setup for running a test, starting with nothing more than a regular image of high-altitude air pressure. Focus on the area in eastern Asia where you see a large island of dark red, and then, with the help of a few hints, see if you can turn all the associated features into a major weather story that is reasonably complete and largely accurate:
Here we go. That red circle must signify the presence of very warm air directly below, probably a strong anomaly in the 10C area. What else could make such an imprint? Just to the north of it, where the green zone is situated, you can see how the edge of that zone has taken on an indented shape that conforms quite well with the size and position of the red circle, suggesting a relationship. Each of the borders of the red and green zones should be home to its own jetstream pathway, and their winds should be reinforcing, so one might expect to see a strong current of jet wind to be active along the space that lies between them.
Meanwhile, the warm air anomaly we expect to see at the surface would have no reason to be there unless it was produced by a large and powerful stream of high-altitude water vapor, so that is something else to look for. It should be coming in from sources farther south composed of one or more large bodies of warm water capable of producing an abundance of evaporation that could be lofted high up in the air without being blocked by heavy cloud cover. For this particular stream location out in the middle of nowhere that could represent a challenge. The Caspian Sea is nearby, but relatively small compared to the ocean bodies that usually produce these streams. The red shading on the map suggests that the best such choice might lie directly to the south, which would make the Arabian Sea a good candidate.
We’re still looking at only the one above map. What else can it tell us? There is one more thing. All of the vapor in the stream we are imagining will have to condense at some point and precipitate. The deep red circle suggests that a considerable amount of vapor in this stream has moved well to the north without being lost to precipitation before everything stopped advancing. Once it did slow down and stop it would naturally “bunch up” and by that means be forcibly compressed enough to reach a saturation point. The jetstream winds we have already pictured are positioned in a way that would cause the whole stream to be fully blocked from further movement, making that general location a good place to look for saturation to develop and produce steady rainfall. Now we can look at all the maps to see how good these guesses have been. First, the anomaly one, which was easy. Note how well it extends straight to the south, which helps to confirm our idea of where the vapor stream must have come from:
What about our guess of the big jetstream wind? Any chance of a disappointment there? Of course not, or I would never have started this exercise in the first place, so there it is, exactly as predicted:
The precipitable water stream is next on our list, and it is every bit as strong as it would need to for such a large anomaly to be created in the mid-latitudes. It has up to 40kg of water in the center, roughly double the amounts of vapor you see off to the sides in places where there is no sign of a high-altitude stream in progress. The Arabian Sea indeed looks like it must be the primary source of the stream, with added participation coming from the Caspian, and maybe even some input from off the side of the big mass of vapor emitted by waters of the Pacific.
Many water vapor streams drop off a good bit of their load as rain along the way, but not this one, except for a tiny bit. We don’t even see clouds until the very end, and then the rains finally appear. One may wonder about how far north the stream would have continued at full strength with no wind jets standing in the way. The utter lack of condensation over the actual lengthy journey to the north is something worth thinking about. Another thousand miles of travel would give that same load tremendous leverage over the increasingly arid lands closer to the Arctic, perhaps leading to another double and another 10C of anomalous warming.
Carl