A bit of map study today. I want to focus only on the close relationship between total overhead precipitable water (PW) and surface air temperatures for any one locality. This is something that climate scientists of all types either do not understand, or refuse to openly recognize, or don’t find it important enough to be worth talking about. I gave you an example of this attitude in yesterday’s letter. The greenhouse energy effect of PW, no matter where and how it is expressed at any one time, may far exceed any other direct effect on temperatures at that moment, and often does so in dramatic fashion. When the existing overhead PW value is normal, or the same as its past average for the location, it has no effect at all. When it is not normal, either higher or lower than average for the day, the effect becomes proportionate in a logarithmic way.
Logarithmic means that each change in average PW value, as I see it, results in a temperature change of about +10C for any doubling of value, or -10C for a halving—repeatedly. Scaled down, still logarithmic, a change of +/- 5C will result from a PW that has moved 41% away from average. PW changes on the higher end, or even greater than a double, occur somewhere almost every day. No matter what the strength, the temperature effect of a PW change becomes evident in practically real time. This is all quite ordinary. There are a number of other ordinary forces, factors or conditions that cause temperatures to depart from normal, but none can be named that have anywhere near this much power, nor ability to act with such immediacy. Aside from the ordinary, super volcanoes and asteroid strikes can certainly exceed PW in power, but fortunately the wait is long between occurrences. We are likewise fortunate that the stronger types of effects from PW changes, like heatwaves or deep cold spells, seldom endure for much more than a week or two.
Turning to the current cold spell, there is an area in Montana where the temperature anomaly for the day is a full 24C (43F) below normal, a truly rare extreme on the cold side. At this same time, far to the north, near the top of Canada, there is an area where temperatures are at least 21C (38F) warmer than normal. Both of these are parts of two extensively large areas that have significant logarithmic differences in PW values, as determined mainly by air flow variations that occur in the upper atmosphere. In Montana the total PW reading is just a little over 1kg, while the Canadian spot reads between 6 and 7kg. That difference, a full two doubles, is enough to account for actual temperature differences, where Montana is now the colder of the two by about 20C. Ordinarily, because of the big difference in latitude, the normal temperatures alone would be reversed by about the same amount These next two maps are worth exploring to observe the full context of actual temperatures compared with actual PW differences for various localities on a much larger regional basis:
The visible intrusion of PW across the heart of Canada has a story of its own, which I will not try to tell today. You can see where it came from, where it stopped, and how its parameters fit so neatly inside the surrounding area of deep cold. There is even an extension out over the Arctic Ocean that is noteworthy. I’ll close with an anomaly map, where you can look for that small area in Montana with the -24 reading, using lots of magnification. According to some forecasts there could be more places like it in the days ahead.
Carl