Did you know that almost 10% of general aviation accidents happen because of weather? And you know what's crucial to avoiding bad weather? Understanding the difference between high and low pressure systems. In this video, we'll look at the four differences between high and low pressure systems so that you can stop safe flight from turning into a scary one. Hello and welcome.
My name is Greg. I'm an FAA flight instructor with over 20 years of experience. And I'm the lead instructor at Pilot Institute, the online school where we help you achieve your aviation dreams.
So. Of the four differences we're going to talk about today, number four is the most important. But to understand these differences, we need to first understand what atmospheric pressure is. Atmospheric pressure, or air pressure, is the force that is exerted onto a surface by the weight of the air above it.
Imagine a column of air stretching from the ground all the way up to the edge of space. The weight of that entire column creates pressure on the Earth's surface. Now, some areas of the Earth's surface have higher pressure compared to their surrounding and some have lower pressure. Now areas with low pressure on the surface are low pressure systems and areas with high pressure are called high pressure systems.
This brings up the difference between high and low pressure system, the movement of the air. Air is going to descend towards the ground in a high pressure system leading to stable conditions. In the low pressure system the air is going to rise away from the ground leading to unstable conditions. But The air just doesn't move up and down, it also rotates. Difference number two is the direction of rotation.
The wind actually rotates around a low pressure system and a high pressure system. Why? Well, it's because of something called the Coriolis effect.
Let me explain. Because of the Earth's rotation, winds don't move in a straight line from point A to point B. Imagine throwing a ball to someone on the other side of a merry-go-round. the ball won't go straight to them.
It will actually curve because you're spinning. That's what happens to the wind on our very own spinning merry-go-round, the Earth. Because of this, the wind rotates counterclockwise around low pressure system and clockwise around high pressure system in the Northern Hemisphere. In the Southern Hemisphere, it's going to be the opposite. But the differences in movement don't stop there.
Difference number three is that the air moves from high pressure to low pressure. To understand how high pressure and low pressure systems interact, let's track the movement of air between two pressure systems. First, the air starts sinking in the high pressure system until it reaches the ground.
Then from here, it's going to move to the low pressure system. At this low pressure system, the air begins rising and then dissipates away from the low pressure system. In another hemisphere, the air moves clockwise around the high pressure system. Then it changes direction and moves counterclockwise around the low pressure system.
Okay, we only have one more difference left. The fourth and most important difference between high pressure and low pressure is the weather conditions. High pressure systems bring good weather and clear sky, while low pressure systems bring cloudy skies and a greater chance of rain, from light drizzle to possibly heavy storms. For pilots, a low pressure system means a lot more than just a rainy day.
A low pressure system can cause turbulence because of the unstable air, clouds, precipitation, dangerous conditions like icing or even thunderstorm. Now to fly near or through one of these systems you need to be careful and stay alert. Sometimes you may need to make decisions like changing the route or even delaying your flight. Now a high pressure system on the other hand means less turbulence.
The stable air associated with this system reduces the vertical movement of the air making for a smoother ride. While high pressure systems promise clear skies there's a catch that you need to be aware of. The clear skies of a high pressure system can also lead to rapid cooling of the earth's surface, especially at night. This can result in morning ground fog or even frost on the aircraft's surfaces, and the fog and the haze don't go away easily in the stable air of high pressure systems. High pressure systems can also cause temperature inversions where the temperature increases with altitude instead of decreasing.
This can also cause reduced visibility and affect aircraft performance. Now with all that being said, visibility in a high pressure system isn't usually that poor unless there's smoke. present from a nearby wildfire for example.
Okay so we've talked about the theory behind high and low pressure systems but how do you find out where they are so that you can actually plan for your flight? Well one of the best places is the Aviation Weather Center website and they've actually made a big update recently. If you're interested in learning more check out our video right here where I walk you through exactly how you can use it.
Thanks for watching and we'll see you in the next one!