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Weather Wise: Wet Bulb temperature

The wet bulb temperature is the temperature read by a thermometer covered in a water soaked cloth, over which air is passed.

LOUISVILLE, Ky. — Meteorologists talk about air temperature every day, and sometimes you've heard us mention the dew point but, have you ever heard of the wet bulb temperature?  

Let's define it and talk about how we use it.  

First off, the "dry" bulb temperature is just your normal air temperature.  

It just means the thermometer is dry.  

The wet bulb temperature is the temperature read by a thermometer covered in a water soaked cloth, over which air is passed.  

So why would we do that?  

Well, when the air is 100% saturated, 100% humidity, the dry bulb, or air temperature is equal to the wet bulb, but when the air is drier, the wet bulb temperatures are lower than the air temperature.  

That's because when water evaporates, it cools the air around it.  

Think about how your swimsuit gets chilly after getting out of the pool.  So, the wet bulb is usually lower than the air temperature.  

We use the wet bulb temperature to find out if large hail or damaging winds could happen if thunderstorms fire up.  

If the wet bulb temperature is at 0 degrees at a lower height, then large hail could easily form and also possibly cause wind damage.  

If the wet bulb temperature is very high at the surface, that means extreme heat and humidity are present.  

A high wet bulb temperature would signal a high heat index and a danger of heat related illnesses.  

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