High Pressure Galor!

With the excellent weather we have been having lately, soon to be interrupted by rain and terribleness, I thought I would take some time to give a quick explanation of what exactly a High Pressure system is. Or as Katrina likes to point out, the H for happy weather.

Let's start with recent forecast discussion from the NWS regarding the upcoming transition from nice weather, to stormy weather.

"THU/THU NIGHT...
MID LEVEL RIDGE BEGINS TO MOVE ACROSS THE REGION WHICH RESULTS IN
FLOW TRANSITIONING FROM ANTICYCLONIC TO CYCLONIC FROM WEST TO EAST.

Lot's of technical jargon in here, which I actually dislike about the NWS weather discussions but nevertheless, lets focus on the first sentence.

When we talk of ridges, we are referring to a large area of High Pressure. So what the hell is high pressure? You can actually take the term literally as a matter of fact. A high pressure system, or in this case ridge, is an area where the atmospheric pressure is higher than surrounding areas. The air in a high pressure system is more dense and begins pushing downward towards land, accounting for the higher pressure we feel. Well, not really feel, but see.

Air flowing down from the upper atmosphere is the exact opposite process that occurs when a storm is forming. Most of us know that clouds and precipitation occurs when air rises and then cools and condenses to form clouds. Sinking air is unable to form condensation in such a manner which is why we usually see clear skies with high pressure.

Another important property of high pressure has to do with the direction that air flows when it reaches the ground. Because of the earth's rotation and land friction, the wind from a high pressure system actually flows outward, away from the center unlike a storm or low pressure system in which we know that the strongest winds are close to the center and flow counterclockwise. These flow distinctions give both a high pressure and low pressure the terms of anticyclonic and cyclonic flow respectively. Anticyclonic flow will never be able to form clouds which is why high pressure is a good indicator of fair weather.

Of course, there is a lot more detail that goes into this process, but at least this gives you somewhat of an understanding as to why those H's on the weather maps mean happy weather!