![]() Heat index is similar to the wind chill index we use in the wintertime, however, instead of wind speeds, relative humidity is factored in with actual air temperature. Relative humidity also goes hand in hand with another common piece of information meteorologists often convey in the summer months, the heat index. Typical summertime dewpoints in Siouxland rarely exceed 70-75°. Anything above 70-75° is just tropical, similar to what you might experience in Florida or the tropics. At around 65°, is when it starts feeling muggy and just overall very unpleasant and the air may even feel a bit “heavy.” Once dewpoints exceed 65° and start climbing into the upper 60s and low 70s, it begins to feel oppressively humid and extremely unpleasant. Once dew points rise above 60°, that’s when it starts to feel much more sticky, humid even. ![]() Once we exceed the 55° mark, that when we start to notice that sticker feel to the air and the relative humidity becomes a bit more noticeable. Generally, dew points below about 55° or so in the summertime equates to drier, more comfortable air. This is when dew point temperature comes in. However, as we get into the warmer spring and summer months, we start to see higher dew points, usually between 50-70°, occasionally a bit higher with a particularly moist airmass. In the winter, dew points typically top out in the 40s and maybe low 50s at times, so even at 100% relative humidity, the air is still fairly dry and comfortable. The dew point is the temperature to which the air would have to be cooled to reach 100% relative humidity, meaning full saturation of the air, at which point, we see dew forming, or precipitation likely occurring. This is where dew point temperature comes in. In general the warmer it gets, the more water vapor the air can hold, and the more relative humidity is felt. This is simply because warm air can hold far more water vapor than cooler air, which is also why you’ll notice we don’t really talk about it being muggy in the winter, even when we see high humidity levels, like for example as a snow storm approaches. ![]() ![]() Which block of air would actually have a higher overall humidity? You might automatically assume the 40° block with 95% relative humidity, however, it would, in fact, be the 80° block with 60% relative humidity. The block of 80° air has a relative humidity of 60% and the block of 40° air has a relative humidity of 95%. To explain this a bit better, imagine you have two different blocks of air: one is 80° and the other is 40°. We’ll start with relative humidity, which measures the amount of water vapor in the air at any given time, relative to the air temperature. You’re probably familiar with these terms, but you might wonder what exactly these different values tell you and what they measure. SIOUX CITY, Iowa (KCAU) - As we head into the summer months, and even throughout the spring, you might here your local meteorologists refer to the dew point, humidity, and heat indices. ![]()
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