Question: What's the dew point got to do with it?
Answer: A lot!
To gain perspective, since spring, I have used the dew point temperature graphic, during almost every forecast on WDRB News. It's that important! Today's dew points are in the middle to even upper seventies.
But recently I have noticed a lot of people asking, "What does the dew point have to do with the humidity?"
To answer this, let's start with relative humidity.
It is defined by the National Weather Service as "the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. Since the latter amount is dependent on temperature, relative humidity is a function of both moisture content and temperature. As such, relative humidity by itself, does not indicate the actual amount of atmospheric moisture present. See dew point."
In lay man's terms? Because it is taking into account TWO properties, it will not accurately tell us how dry or sticky it is outside. BUT the dew point will.
For example, in the morning or winter, it is common to see the relative humidity at 90-100%, because the air temperature is close to or meeting the dew point, but that doesn't mean it is actually sticky out. The winter is a very dry season.
Simply put, the dew point measures the moisture in the atmosphere. It is also the temperature to which air must be cooled in order to reach saturation.
*When thinking of dew points remember this: The higher the dew point = the more moisture present in the air = the more uncomfortable it will feel.
Therefore, when we are talking about muggy, humid, sticky, "air that you wear" days - you will hear the WDRB Weather Team mentioning the dew point rather than the relative humidity, because it is the more accurate term to use.
On the image below, the highest dew point in the regional is Peoria, IL - so that is the most uncomfortable location. While in Pittsburgh, the dew point is at 56 degrees, which is very pleasant and the driest location.
To understand this even more, you can break dew points down into categories of about 5 degrees.
A dew point of . . .
60-65 degrees: A magical number when you start to notice the humidity.
65-60 degrees: It is steamy and getting uncomfortable.
70+ degrees: Miserable and oppressive.
So today we have dew points ranging from 69 degrees to 79 degrees. Which is a very sticky to miserable day. Not only that, but we also have very high air temperatures as well today.
Taking into account the air temperature PLUS the dew point = heat index or the "feels like". As air temps over the next few days rise to the mid 90s with dew points in the low to mid 70s, it will feel like the 100-107 degrees! You can get an idea of how the heat index works with this calculator!
Because the temperatures and heat index is going to be so high, remember we are under a heat advisory until Saturday at 7 pm. Stay cool and take care of yourself! Read up on some heat safety guidelines here.
We are also tracking some showers and storms for your Friday and weekend. Be sure to tune into WDRB News tonight with Marc and Rick to find out when and where they are expected to be.
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-Meteorologist Katie McGraw