This podcast talks about some of the significance of dew points. Dew point is defined in this podcast. This podcast also discusses the most spectacular (my opinion) weather variable (and its even man made) in regards to humidity. We talk about the Midwest corn fields. The transcript is as follows:
Unknown 0:08
Good morning, everyone. It is Monday August 2. I wish this could be part of the humidity podcast. But that one is just too long already. I wanted to just discuss, why is it so rare to have at Dewey dewpoints in this country? Why? Why do we not experience the yet the other countries on by the Red Sea in the Persian Gulf, they do experience 80 degree dew points well into the 80s. And we don't what's wrong over here? We have the Gulf of Mexico. So what exactly is wrong, the Gulf of Mexico is really, really warm waters. So first, I, maybe I should explain what dew point is, like I did in the previous podcasts, a couple other podcasts. vouchsafed very quickly, the dew point is the most accurate way to measure humidity in the air, it's the temperature at which the environment would become saturated. So again, we have a large jar holds more water than a small jar, heat expands. So the warmer it is, the larger the air molecules are, the more water vapor it could hold. Relative humidity is how much water vapor is the air holding compared to what it could hold. So what you end up with is 90 degrees with a relative humidity of 50%. Relative humidity of 50% mix is a usually the dew points about 20 degrees lower than the temperature. It's that's not 100%. exactly correct. It depends on what the temperature is. But if you have an air temperature of 90 degrees, relative humidity, 50%, that's holding as much water vapor at 70 degrees could hold. So the relative humidity of 100%. When the temperature 70 would produce a relative humidity of 50% when the temperature is 90. And a lot of times by the way, and 90 degree heat in the afternoon, drops to 70 at night. So it's not uncommon to see the relative humidity close to 100% in the morning, and then drop the 50% in the afternoon. It's not that the humidity is dropping the humidity staying the same. The only differences is the relative humidity relative humidity is important. More so I think it's more important for weather forecasters. And dealing with the environment how much the what are the chances that the precipitation will be evaporating before it touches the ground. And it's more important for forecasters, it doesn't play To my knowledge, it does not play a significant role. And for our purposes, in terms of how the air feels, the only time it would play a significant role is when we're dealing with borderline humidity. So dew points of 60 or higher are considered humid, dew points of 70, or higher or 72 or higher, are considered oppressive, sometimes maybe even Upper 60s. So when dew points are in the 70s, it's going to feel humid, no matter what, when dew points are in the 60s, it's gonna feel humid. But when temperatures get really hot, it's not gonna feel humid, it's gonna feel more dry, there still will be a heat index of a degree or two, but it's gonna feel a little bit more dry, the relative humidity is so low in the morning, it's gonna feel humid. And when dew points are in the 60s, I think you do need a higher relative humidity in order for it to feel for it to have that moist feeling. And I think if if it's in the Upper 50s with the relative humidity of 100%, I think it's also going to have that moist feeling as well. So I think that's where the relative humidity plays a role and comfort level in when dew points are in the 60s, and also in the winter in terms of that damp feeling. But again, we go back to our question is why are dew points higher than 80 so rare here in this country. Now one thing you have to realize is that the temperature always has to be higher than the dew point. So the only time dew points of 80 degrees could occur is if the basically the nighttime lows are going to be 80 degrees. I mean, the two points with the Germans will prevent high dew points will prevent the temperatures from dropping too low at night. The temperature the air temperature might be able to drop the dew point by a degree or two but they will prevent those temperatures from dropping.

Unknown 4:45
So what you need to have an 80 degree dew point. Basically what you need is a body of warm water. The coastal cities I've noticed on the Gulf of Mexico tend to have dew points which are 10 degrees lower than the water temperature Now why should that be? Why can't it be they have dew points which are equivalent to the water temperature, the air temperatures that come off of the water are about the same as the water temperature. So if you have the water temperatures at eight degrees in the Gulf of Mexico, the wind comes in off the water, and nighttime, that air temperature will be, I guess, since it's night, will be a little bit less than 88. Maybe at the coast, maybe 86, something like that. And during the day, because the sun is out a little bit higher, let's say 90, well, what about in terms of the moisture level, you have air coming in off of a body of water, hundreds of miles of a body of water, which has been 88 degrees. So let's say the dewpoint should be pretty close to 88, maybe 80, maybe also 86 or something like that. I think the that the human? Well, I know that humidity human airs is lighter than drier air. I know we don't tend to think like that. But it is. So a baseball will fly higher in the human air mass than in a dry air mass. it's counterintuitive, but that's the way it is. So that humid air rises above dry air. So I think the real humid air goes a little bit above the surface. And then on the surface, we're left with very humid air, but not as humid as what just came off of the water. That's what I think. But in any case, it's about 10 degrees lower than the water temperatures. So the water temperatures, for example, today, 86 degrees in one part of Texas 89 degrees in a different part. And then off the coast of Florida, it's very similar. There's one part which is 85. And I would imagine Miami, it's probably close to 90 by now maybe even 90. I think maybe one time I've heard of a 91 degree water temperature, but the water temperatures tend to be in the Upper 80s. So the dew points right on the coast are going to be in the Upper 70s, they're not really going to hit 80. On occasion, they might hit at the there's so why are dew points in the 70s so common, it's because we have a clear mechanism in this country to produce 70 degree dew points. We have it's just a natural phenomenon. When winds coming off the Gulf of Mexico, we're gonna have 70 to 70 degree dew points, there's only one variable needed winds off of the Gulf of Mexico, that's all you need. And then you have 70 degree dew points. That's it. To produce 80 degree dew points, you need at least two variables. You need winds coming in off of the Gulf of Mexico and they continue blowing and blowing and blowing into Iowa. If you can get those winds to go into the cornfields of Iowa and there's no drought, it's a year of a successful corn crop. That's when we get two points in the 80s the cornfields or they are able to bring the dewpoints higher into the 80s cornfields are like a the most ideal. Nothing could be greater than a cornfield, to raise the dewpoint there's like nothing that could possibly exist, that can raise the dewpoints so high, no matter what is going on. The cornfield will always be able to raise the dewpoint. And the reason is because corn fields produce enormous amount of its starts with the T but we'll just call it that the plants are EVAP they are sweating, plants sweat forgot it's there's a word for it. And that sweat is evaporating, it doesn't produce quite as much as the ocean does. Not quite as much. But remember the fact that the oceans 5000 feet deep, that doesn't increase the evaporation rate, you just need a little bit of water on the surface for there to be evaporation. So the oceans producing evaporation the cornfields also producing enormous amounts of evaporation. The thing with the cornfield is that the cornfield is just as hot as the air temperature. So therefore the dew points could go much higher. The maximum dew point ever coming off the Gulf isn't can't be higher than the water temperature. It can't be higher than the air temperature.

Unknown 9:21
So I think the highest dew point ever recorded in this country was the dew point in 90 degrees which occurred in Louisiana and in Wisconsin. So probably there was water temperature of 90 and that particular time somehow the dew point ended up being 90. That air did not end up going higher than the surface it ended up being on the surface 90 degrees. So the cornfield can raise the dew points of about to raise it usually around five degrees. And then if you have solid vegetation with moisture in the soil, going all the way from Louisiana. There's no drought to Oregon so you can maintain the 78 three dewpoint coming in off the Gulf of Mexico, it could man pain could remain 78 probably dropped a little bit into Missouri 75 but then hits the cornfields and it goes up from 78 to 83 degrees, sometimes even from 75 to 83 degrees. When you have places by the Persian Gulf and the Red Sea, so there you have the water temperatures are hotter, and therefore the dew points are higher dew points are in the 80s because the water temperatures are in the 90s. And if they would have cornfields there as well, those corn fields would also raise the dewpoint by five degrees. They don't have corn fields over there as far as I know. So you have the dewpoints coming in off the water in the low 80s, sometimes mid 80s, but usually low 80s. If there would be a cornfield there, you would have dew points approaching 90 degrees over there. Maybe there are some type of cornfield, I don't know. But they don't have the cornfield. So dew points in the 80