Today I will zero in on the northern version of the high-altitude air pressure configuration (HAPC) zone we saw yesterday in the global comparison, now just slightly altered. This offers a prime example of how its shaping on the map, which represents actual changes in differences in air pressure gradients, has a profound influence on major weather events at the surface. This influence is mainly transmitted through a process that includes jetstream organization, the movement of concentrated bodies of precipitable water (PW) at that altitude and the powerful greenhouse energy effect of PW on surfaces below, at whatever locations the PW passes over during its relatively short lifetime. I will start with the HAPC map and construct some predictions of how PW movement will unfold that can be derived directly from studying this one map alone.
The first prediction is based on a prior assumption that a large volume of evaporation in the Caribbean Sea area will rise to high altitudes as concentrated streams of PW. They will quickly encounter jet winds in the red zone that will carry them toward the center of the Atlantic and then straight north. When this jet pathway turns around and heads south a significant remnant of PW will break free and continue on northward, where there are spaces occupied by other jetstream winds associated with blue zone and green zone fringes that are close together, enabling wind movement in contrary directions. In spite of the confusion, a significant remnant of PW will find a way to continue moving north, past Iceland, then Svalbard and on into the heart of the polar zone, where a true cyclonic wind pattern might be able to set up and allow vapors from the PW to spread out widely.
The second prediction sees the high probability of a powerful blue and green combination jetstream wind, with red zone backing, moving downward from Alaska into the center of the 48 states, where it turns around and heads back toward Hudson Bay, probably much weakened by now because there is no strength being added by red zone winds, eventually reconnecting with the starting point in Alaska. The deep blue zone that is encircled by this wind is in position to largely be kept free of penetration by incoming PW, thus maintaining very cold temperatures throughout the surface beneath. Areas all around the blue zone, shaded in various tones of green, will remain open to amounts of PW penetration that could possibly be abnormal, causing warming to occur at the surface.
Here is how everything is turning out from a jetstream point of view, which is the safest thing to predict from the imagery on any HAPC map. The cyclone in the center of the Arctic, while not a given in this situation, is a very extraordinary feature; it definitely doesn’t belong there at this time of year, and would never appear if the blue zone were all in one piece, as it should be.
The PW part of the prediction has worked out as well as could be expected, perhaps helped by the fact that I did some cheating moving ahead with it. A dry interior for any deep blue zone is always a safe prediction. Also, jetstream winds heading north, both strong and weak, will almost always pick up and carry as passengers any amount of PW that becomes available, losing most of it if and when they later bend around sharply and head back south again.
Lastly, a view of the anomaly map, to see the final outcome of the two predictions. The warm anomaly in the polar zone was broader than I thought it would be but not warmer. The area inside the deep blue zone of the HAPC is not just very cold, for lack of overhead PW, but much colder than normal, with spots in a lower than minus-20C range. The biggest surprise of all on the map is the warm anomaly in the Hudson Bay area, where the reading is a huge +21-24 C over a pretty large area. It was caused by a PW value just shy of 10kg that somehow accumulated on the inside of a large bow-shaped curve bordering a large area having few outstanding distinctions. This all adds up to a larger phenomenon that should be predictable and thus worth adding to the general list of things to look out for.
When all is said and done, I think the highly misshapen HACP in the NH is the main reason why we are currently seeing a net anomaly of +1.1C over the last three decades, in spite of the fact that so many deeply cold parts are in play along with the warm ones.
Carl