MEMPHIS, Tenn. (WMC) - When talking about the mugginess of the air, meteorologists almost always point to the dewpoint rather than the relative humidity.
In this episode of The Breakdown, we explain why dewpoint matters more than relative humidity when describing how hot it feels outside on a given day.
Relative humidity is just that, a measure of how much moisture is in the air “relative” to the air temperature. A 100% relative humidity at a temperature of 48 degrees and a dew point of 48 will not necessarily feel humid out, but according to our scale the RH is capped out.
Now on the flip side, a relative humidity of 51% with a temperature of 93 degrees and a dew point of 72 degrees would feel downright gross outside as the muggy factor will be through the roof.
While it can be a bit difficult to figure out what is humid when using the relative humidity values, it is much easier to understand dew point to explain the “real feel” temperature outside.
According to the National Oceanic and Atmospheric Administration, “The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%. At this point the air cannot hold more water in the gas form. If the air were to be cooled even more, water vapor would have to come out of the atmosphere in the liquid form, usually as fog or precipitation.”
That basically means that once temperature equals the dew point it is saturated and our RH is 100%, this could also cause fog at night.
That is why the First Alert Weather Team will uses the dew point scale to show how it will feel outside. When the dew point is around 50 degrees then it will feel really nice outside. While when our dew point starts to approach 70 to 75 degrees we need to start watching out as the heat and humidity combined could cause issues.
When our body starts feeling temperatures higher than the actual air temperature that is what is considered a heat index. The National Weather Service does use Relative Humidity versus the temperature to figure out the heat index value scale.