Humidity versus dew point

Since I was little, we always watched the weather. Mom and Dad and us boys would stay up until the weather was off, and then it was bed time. Now that I'm older, I still watch the weather. One thing I always pay attention to is the humidity. Never mattered in Nebraska, but boy it does here in Missouri. But something that seemed to matter even more than the humidity is the dew point.

Years ago when I was in college in Chadron, Nebraska, I had some openings to take some electives. A couple classes sounded fun, so I took a graduate-level course in statistics and a beginner level course in meteorology. I had a blast in both courses. We had to develop some type of statistics problem, gather the data and work out the statistics on it. I did solitaire. It seems like I played a million games of solitaire recording how far I got and cards left and games won (0). It was fun.

Meteorology was a different ball game. It was fun, but at the same time took a lot of time and study and observation. I enjoyed it. One thing we had to use was a sling psychrometer. This was the gizmo that one used to measure the dew point of the air from which one could then calculate the relative humidity.

There was a short metal rod 6 to 8 inches long. On one end was a short rope kind of deal and a handle which allowed one to twirl the whole gizmo in a circle. On the other end of the metal rod was a thermometer with a foam covering. It's been 50 years since I used one, but we recorded the temp when the sponge was dry. This was the dry bulb temp. We then got the sponge wet and went to spinning the sling psychrometer in a circle. The movement in the air would cause the water in the sponge to evaporate, which in turn would lower the temp of the thermometer. The wetter the air the less the water evaporated so there was little change in temperature between the dry bulb temp and the wet bulb temp. But the dryer the air, the greater the water evaporation which lowered the temp on the thermometer. Thus there would be a greater difference between the dry bulb temp and the wet bulb temp.

A simple example would be after I've worked outside on a hot summer morning, and I'm wet from sweat. I walk in and sit down in my easy chair and nearly freeze because the window AC unit is blowing right on me. So I cool down quickly because of the AC, but even more because my sweat is evaporating. Once my clothes get dry, the AC doesn't even feel cold. I no longer have sweat evaporating, which super cools me down.

Relative humidity (RH) and dew point are kind of confusing. The dew point is what really indicates how hot and muggy the day will be and not the RH. The higher the dew point, the more moisture there is in the air. This directly affects how "comfortable" you will feel outdoors. If the outdoor air temp is exactly 100 degrees, and we wet the sponge on our sling psychrometer and spin that sucker, and the temp now reads 75 degrees, we have a dew point of 75. At a dew point of 75 degrees the air will feel wet even with the 100-degree day temp. And even if I sweat and get my clothes wet, I can't evaporate enough moisture to cool me down. A fan will provide air movement, which will help evaporate the sweat and I'll cool down.

Now for an example or two. The other day here in Scott City, the air temp was 87 with a feel-like temp of 91. The humidity level was 49% with a dew point of 66 degrees. But in Arthur, Nebraska the actual temp was 88 and the feel like was 88. However the humidity level was 27% and the dew point was 50 degrees. In Tucson, Arizona, the actual temp was 108 with a feel like of 108. However the humidity was 12% with the dew point being 45 degrees. If we were to work the same amount of time in each of the areas with about the same level of exertion, we'd sweat about the same. However, our clothes would be probably wet in Scott City with a dew point of 66, not as sweaty in Arthur, Nebraska, and even dryer in Arizona.

The difference in comfort levels between a dew point of 66 degrees in Scott City and 50 degrees in Arthur and 45 degrees in Arizona is a lot. One chart I looked at felt that anything 55 degrees and under for the dew point was pleasant, 56 to 60 degrees it was comfortable. However, from a dew point of 61 to 65 degrees this chart said it was getting sticky and the next step of 71 to 75 was oppressive. Anything with a dew point of over 75 is miserable.

When the dew point is high, the level of moisture in the air seems so thick one can almost feel the wetness. The air is heavy and it's hard to breathe. For those with lung problems or breathing problems, high dew points spell trouble and pretty much mean one has to stay indoors in the AC. One place I was reading said, "So if you want a real judge of just how 'dry' or 'humid' it will feel outside, look at the dew point instead of the RH. The higher the dew point, the muggier it will feel."

So when a friend of yours says their weather is hotter than yours, find out what their temp is and what their dew point is. Some will have a higher temp then we who live in Scott City, but darn few will have a higher dew point.