Another perfectly clear example of how strong jetstream winds are able to block the movement of streaming water vapor that has entered the upper atmosphere wind system, in this case causing a cool temperature anomaly at the surface below. Please focus on the large cool anomaly centered on the coast of southeastern Canada, surrounded on all sides (except for a shaft at the very top) by warm anomalies:
Next, we see that the total precipitable water (TPW) reading within this anomaly region, top shaft included, is clearly much lower than readings tied to all the warm anomaly zones around it. We have no available data for daily average TPW readings for any of these regions, but can presume that the difference between warm and cool would not be as great as the current separation. The cool region should normally be higher than the 8-9kg we see here and the warm zones lower than seen:
The differential requires an explanation, and regular readers know what it will look like. Here is today’s jetstream wind image:
The kind of wind you see here could never affect the movement of water vapor that exists in the lower part of atmosphere, which largely constitutes the 8-9kg of TPW that remains in place. Low-level vapor can vary for a different set of reasons, possibly causing anomalies, but they would differ in timing and scale from what we see in this situation. Jetstream winds can only affect increments of water vapor that has managed to move up from the surface and gain access to the higher-up wind system, the exclusive home of all jetstreams. Together, all of the winds in the upper system are a mixture of faster and slower, but never calm, and they all have a preference for blowing from west to east in each of the hemispheres. Most are not as speedy as the jetstream winds, which only arise on certain well-defined pathways and are of varying speeds themselves. The pathways are determined by the physics of air pressure differentials, just like the way things work for wind pathways in the lower wind system, but the manner of configuration of actual patterns of these differentials in each system is not the same.
Jetstream wind pathways, while generally directed from west to east, are often seen on routes that wobble to the north or south, with no particular bias either way. Bodies of water vapor that enter the upper system also tend to move toward the east but otherwise have a bias for moving toward whichever pole is at the center of the system. This convergence will commonly lead to an encounter with a jetstream wind that happens to be in position to block forward progress. The above illustration shows what the result will be like as long as the jet wind is of sufficient strength, which is undoubtedly true in this case.
This last image is only meant to show the cause of the position held by the blocking jet wind, as found on a regular pathway tracking the fringe of the green-shaded zone. Also, be sure to take note that a very warm anomaly is still sitting over much of the Arctic Ocean, just as it has been doing every day for the last two weeks.
Carl