The Heatwaves of 2012

Air dynamics of high pressure systems can add as much as 30 degrees to the normal temperature. The dynamic of high pressure happens because air in a high pressure system is getting pushed down. Air headed down heats at the “dry adiabatic lapse rate” of roughly 6 degrees every 1,000 feet. The air in a high pressure system gets pushed down because it has nowhere else to go – active rising storm system air from surrounding regions pushes air up, making storms happen, and the air runs out of room, heads back down. High pressure systems really aren’t systems at all, just the backside of storms. So it goes to figure the hotter the heat above what the temperature would be normally, the stronger high pressure.
Direct sun plays a role as well. As seen in places like Coachella Valley and Death Valley, the sun heats the ground and warms the air. The rises because it is hotter and lighter. When a high pressure system is in full swing over these valleys, the heated air’s movement is caught up in the larger system’s downward air movement. That air comes back to the ground, hotter than it was when it left, making the surface hotter. This circulation of air over these valleys from the ground, back to the ground, on the very hottest days, repeats about 6 times (as I recall from the diagram at the Death Valley Visitor Center). On a very rare day that starts out hot to begin with, a seventh cycle may complete, resulting in a world temperature record. Death Valley’s record high is 134 degrees!
So far out West we have benefited from strong Canadian cold fronts and cooling Pacific breezes and winds to provide comfy and sometimes downright cold air. It’s ironically displaced air from Canada by surging hot high pressure air back east. A long lived and unshifting high pressure has heated up a vast area back east, kept there by the wild dry winds of the west that have fanned fires on already drought-stricken forests.
This week, the high pressure area is finally on the move, to its normal spot out West. The change in upper air pattern started late two weeks ago, touching off a spectacular derecho storm that still has people left without electricity.
This will be the first time this summer a normal Mexican High asserts its presence. And as normal as it appears, it still seems to have odd characteristics. It’s stronger than a normal Mexican High. Under it, temperatures are expected to surge well beyond normal summertime heatwave temperatures.

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