This transcript was edited for clarity and brevity
Bill Burton: It's time for us to take a look at the Science Behind the Forecast as I'm joined by WAVE 3 meteorologist Tawana Andrew. Good morning, Tawana.
Tawana Andrew: Good morning. For today's topic, we're going to, let's just say, using a bad pun, we’ll feel the pressure.
BB: Yes, we will definitely feel the pressure. We're talking barometric pressure today. Explain this concept to us, please.
TA: Barometric pressure, or atmospheric pressure, basically measures the weight of the air in Earth's atmosphere. So you'll have atmospheric pressure being the greatest where air molecules are more densely concentrated, so closer to Earth's surface. As you start to climb in altitude, then the air becomes thinner, because there is a decrease in the number of air molecules present. So that's why you'll feel the difference in pressure, especially as you climb a mountain, if you're that adventurous, or something like that. So scientists usually measure barometric pressure using the unit of atmosphere, because they can't make anything simple.
BB: We can't have anything simple. Of course not.
TA: No, you got to make it complicated. And in the U.S., we make things a little bit easier, where barometric pressure is usually measured in inches of mercury or millibars. That makes sense, right? So, one atmosphere, because, once again, not easy.
BB: One atmosphere, okay.
TA: One atmosphere, or the standard atmospheric pressure at sea level, is equal to 29.92 inches of mercury. In millibars, that is 1,013.2 millibars.
BB: All right, I’m writing all this down.
TA: Good, because I will test you on this. Millibars is usually what you'll hear meteorologists on television, especially using in terms to talk about atmospheric pressure. So keep that in mind. But if you want to get real fancy and dive into the science of it all.
BB: You know I love to get fancy.
TA: The additional units you could use are millimeters of mercury for our metric friends. Or if you really want to get fancy, there's pascals and hectopascals.
BB: Hectopascals. Yeah, that's very fancy.
TA: Yeah, don't get that tattooed on you. So when barometric pressure drops, it usually indicates the approach of unstable weather. So you'll hear us talking about low pressure systems. That is where the surface air is rising. So at the ground, you get that drop in atmospheric pressure because of that rising air, and that usually leads to clouds and precipitation and strong winds. And the other side of everything, high pressure systems involve dense sinking air, so that air is falling towards the surface, and that usually ends up with clearer, calmer weather in an area. So for normal atmospheric pressure ranges, that could be anywhere between 965 millibars or 1,040 millibars. So that's our typical range.
The lowest atmospheric pressure ever recorded on Earth was 870 millibars, that was in the Pacific Ocean west of Guam as the eye of super typhoon Tip passed overhead. That was back in 1979. And then the highest barometric pressure ever recorded, that was in Agata, Russia, that was in 1968 and that was 1,083.8 millibars. So that pressure was comparable to being nearly 2,000 feet below sea level, while the actual location was 826 feet above sea level, so that was an incredibly high barometric pressure for that area.
