It’s an interesting day for map study because of all the bending and sprouting on the 500hPa air pressure map. The imagery on this map, as you may know by now, is basically established as a physical response to the layout of air temperatures on the surface below, which will be shown on the following map. That correlation is about 90% solid and clearly understandable, while the other 10% has some fuzzy qualities. Anyway, this air pressure imagery is what it is, and will set the stage for most of what happens as a follow-up over the course of the day:
Here is the surface temperature map. You can see how well the border of the blue zone above fits in with the border of the blue zone on this one, which represents freezing temperatures or less. Most of the fuzzy-fitting zonal borders that we see belong to the green parts:
Let’s just move on, and see what happens to the two major jetstream pathways that are governed by standard air pressure differentials as marked on the map by the outer fringes of the blue and green zones. The blue zone pathway today has some sharp bends to contend with, but nothing like the twists and turns on the green border. See how obedient the jet winds are to all such pathway deformation, making every effort to stay on track no matter where the tracks are placed. One other major pathway, the one found in the interior of the red zone, does not offer any such difficulty today, nor on most other days, letting its winds follow a relatively straight line.
The jetstream winds that emerge on the blue and green zone pathways are the ones that have the greatest effect on the movement of precipitable water (PW) concentrations. In today’s setup the PW streams have an unusually peculiar assortment of consequences, as depicted on the next map. When tracing out the connection, there is one basic principle that always needs to be kept in mind: when jetstream winds are heading poleward they will pick up and carry any available PW concentrations in that direction, but that is not the case when they are headed more toward the equator. (They do tend to carry PW streams in a horizontal mode for long distances.) Also, any time a pathway bends from poleward toward the equator, its wind will tend to weaken, allowing PW molecules to spill out and keep moving toward the pole on their own. You can watch this sequence unfold in places every day.
When high-altitude PW concentrations move poleward they are often able to generate greenhouse energy effects that are well above the daily averages for surfaces down below, which otherwise are more dependent on ambient, low-level PW concentrations for a warming effect. (The two sources of PW, high and low, always combine their energy into one total effect.) The immediate result will most likely be warm temperature anomalies. When jetstream winds are positioned in such a way that PW streams are held back from advancing the total amount of greenhouse energy reaching the surface is likely to end up below average for the day. On this last map we can see how both kinds of results developed today in quite a variety of peculiar situations, because so many jetstream winds, some quite strong, were chasing around in all sorts of directions. The large cold anomaly over much of North America is obviously the work of strong winds that are positioned in a manner unfavorable for PW transport. Elsewhere, see how many of the warm anomalies have been set up by jets that must be full of PW and are able to carry their contents poleward over considerable distances—most especially on the track that runs up through Europe:
Carl