Q. Hey weatherman, why don’t you show the relative humidity during your weathercasts?
A. In the 16 years I’ve been doing weather, I’ve gotten that question a lot. Humidity is not a very good indicator of how humid or in most cases muggy the air really feels.
Relative humidity is just that — relative. It is relative to the temperature and moisture content of the air. Or a measurement we use called the dew point.
Here is an example of what I mean: On a hot, sticky, uncomfortable summer day, we can have an outside temperature of 97 with a dew point temperature of 55. This gives us a relative humidity of about 25 percent. On a comfortable, warm, spring day we can have an outside temperature of 72 with a dew point temperature of 42, giving us a relative humidity of about 35 percent. Although the summer day feels more humid than the spring day, its relative humidity is actually lower.
The dew point temperature is the temperature at which the air can no longer hold all of its water vapor, and some of the water vapor must condense into liquid water. At 100 percent relative humidity, the dew point temperature and the air temperature are the same. While relative humidity is a relative measure of how humid it is, the dew point temperature is an absolute measure of how much water vapor is in the air. In very warm, humid conditions, the dew point temperature can reach 60 to 65 degrees, but it rarely exceeds 70 degrees around here.
On KMVT you will see me showing what I called the “Muggy Meter.” Dew point temperatures 40 degrees or lower are fairly dry and pleasant or comfortable. When those dew point numbers reach 41 to 45 degrees it is noticeably humid. Dew point temperatures between 46 to 50 degrees puts us in the muggy category and into the low to middle 50s it’s sticky. Then 56 to 60 degrees is yucky with any dew point above 61 degrees it is just plain miserable.
Wednesday and maybe even Thursday we could feel a little muggy as our dew points will be close to 50 and upper 40s. Eventually the air will dry out heading into the end of the week and into the weekend.