![]() ![]() Picture a cool, crisp October day in southeastern North Carolina. The dew point temperature told that story consistently. While the actual amount of moisture in the air has not changed from morning to afternoon, the relative humidity has dropped by half! Would you be any less inclined to break a sweat, need an extra glass of water, or seek an air-conditioned space in the afternoon versus the morning? No way! To you, the air on this summer day is consistently oppressively humid. "97 over 75" produces a relative humidity of only 50%. But, by that time, the actual temperature of the air has heated up with the daytime sun to a sizzling 97 degrees. Now, in the afternoon, there is still a ton of moisture in the air, and the dew point temperature remains a sweaty 75 degrees. "75 over 75" produces a relative humidity of 100%. At the dawn of this day, the air temperature is a balmy 75 degrees too. Let's say there is a lot of moisture in the air on this day, and the air's dew point temperature is a stifling 75 degrees. Take a standard sultry August day in southeastern North Carolina as an example. But, the higher the air's temperature rises above its dew point, the lower the relative humidity gets. When the air's temperature matches its dew point temperature, relative humidity is 100%. Relative humidity is a much more variable, much less reliable gauge of comfort because it is, well, relative to temperature. SO WHY IS RELATIVE HUMIDITY A LESS-RELIABLE GAUGE OF COMFORT? Of course, every person's tolerance to humidity is slightly different, but this scale of dew point with respect to comfort is almost universally applicable for southeastern North Carolina. But, in situations when the dew point temperature dips below 55, you'd likely say "it feels crisp" outside. In the attached graph, you'll notice that in situations when the dew point temperature is exceeds 70, you almost certainly would say "it feels very humid" outside. In southeastern North Carolina, dew point temperatures can dip well below 30 degrees in the wintertime, while summertime dew point temperatures usually soar to well over 70 degrees. The higher the dew point temperature, the more humid the air. The lower the dew point temperature, the drier the air. Think of it as the temperature to which you'd have to cool the air to get it to saturate. WHY IS THE DEW POINT TEMPERATURE THE PREFERRED GAUGE OF COMFORT? The dew point temperature is an absolute measure of moisture in the air at a given time. In short: dew point is a fixed target, relative humidity is a moving target. Viewers have asked us the fine question, "When discussing humidity or comfort levels, why don't you give the relative humidity instead of the dew point?" The reason: dew point temperature is a much more consistent and reliable gauge of your comfort level than relative humidity. When you watch your First Alert Forecast, you may hear the meteorologist reference the dew point temperature in reference to how humid or how comfortable the air might feel to you. ![]()
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