Today’s letter will highlight some new observations related to jetstream activity within the red zone on the 500hPa (high-altitude air pressure configuration) map. A feature is emerging that I have not previously taken into proper account, one that looks like it will be around for awhile and be needed for explanations of future developments. One of the future developments we can expect will be a shrinking of the overall size of the green zone on the 500hPa map. The next two images contain a perfect example of a special relationship that I have written about before. showing how the outside perimeter of the green zone—which is created at an elevation about three miles above the surface—is primarily determined by existing air temperatures close to the surface, for as long as they stay on the cold side. When those air temperatures reach or exceed about 12C, expanding the air above as they do so, the upward pressure will flatten out the current isobar differentials in a way that moves their lineage back toward colder places. Outer parts of the green zone then convert to a pale shade of red, signifying an expansion of the latter’s full size. On the temperature map you can track down the geographical location of the 12C line and see how well it matches the green zone perimeter. The 12C line is virtually certain to keep moving inward as temperatures rise over the next couple of months, taking the green-zone perimeter jetstream pathway in with it, but is in no danger of disappearing. What could disappear, almost completely, are the now multiple pathways established by the multiple pieces of blue-zone perimeters. Without the assistance of any close-proximity blue-zone jet winds the green-zone jet winds will not be able to step back up to their former high velocities unless they can gain exposure to similar partnerships with red-zone jets. That prospect may exist, and it gives us every incentive to learn as much as we can about the activity of those jets and the nature of their pathways.
Now we will quickly move on to today’s jetstream map, keeping it close to the 500hPa map for ease in making numerous visual comparisons:
To be sure, this is a messy looking picture, not easy for anyone hoping to sort things out. Start by seeking out the regular green-zone isobars that stretch from one side of this image to the other on a wavy line. They are right where they belong, but half the time are conflicted in a way that makes them hard to find. Then look for any remnants of blue-zone jets, only a handful of which remain visible in this state. The red-zone jets, on the other hand, are more prominent than ever. In fact you can now see two separate and well-extended pathways, each of which has an abundance of high-velocity wind activity. Previously, in either hemisphere, I have only been able to see one pathway of real extension and prominence plus an occasional short segment here and there. This is different, now showing two distinct high-profile tracks with one staying inside the other.
The innermost and quite wavy red-zone track, located completelywithin the area of lighter red shading, stands out best when it is heading southward in the Atlantic far off the west coast of Spain. To the south of it one sees a long and less wavy track holding closer to the edge of a darker-shaded red area. Farther south yet, emerging from Sudan as it heads east, one can pick out what appears to be yet another pathway, which I think is better identified as a branch of the outer red pathway because on close examination it keeps the same color shading, subject to scrambling effects. The large patch of the very darkest red shading across much of northern Africa is the natural result of very hot surface temperatures and the upward expansion of air and associated pressures that go with so much heat.
The overall pattern of jetstream behavior that is now rapidly evolving in the NH promises to make significant changes in the way streams of PW concentration will be navigating their poleward-directed movement in the months ahead. I suspect it will be easier to break through barriers and make more headway because of all the weaknesses within the green perimeter, but feel less confident for now when it comes to projecting a possibly expanded impact from the newly-paired red-zone jets.
Carl