What’s a Heat Dome? And What’s It Doing to Robertson County
ROBERTSON COUNTY, TENNESSEE: (Smokey Barn News) – There actually is some interesting science behind what we’re experiencing across Middle Tennessee.
An exceptionally powerful “heat dome” is sitting over the Tennessee Valley. The National Weather Service has measured this upper-level ridge at near-record strength for this time of year.
Under a heat dome, air slowly sinks. As it descends, it compresses and warms, which lowers the relative humidity. The same ridge suppresses clouds and rain, allowing almost continuous sunshine to heat an already very dry landscape.
That’s why you can see something unusual like 98° with relative humidity in the low 30% range. The air still contains moisture — dew points have generally been in the 60s — but it isn’t carrying the oppressive tropical moisture that can push a 96° afternoon into the 110°-plus “feels like” territory.
In other words, it’s brutally hot, but our sweat can evaporate somewhat more efficiently than it could during one of our muggy Tennessee summer days. So we’re getting a taste of California heat.
And yes, this heat dome is exceptional. Meteorologists have described the upper-level high over our region as one of the strongest on Earth this week.
So if you’ve stepped outside and thought, “It’s nearly 100°, but somehow this isn’t as unbearable as I expected,” you’re not imagining it.
WHY DOES LOWER HUMIDITY MAKE EXTREME HEAT EASIER TO TOLERATE?
Your body cools itself largely by evaporating sweat from your skin. That evaporation carries heat away from your body.
When humidity is high, the air is already holding a lot of moisture, so sweat evaporates more slowly and your natural cooling system becomes less effective.
When humidity is lower, sweat evaporates much more easily, allowing your body to shed heat more efficiently.
That’s why 96° with relatively low humidity can feel considerably more tolerable than 96° on a muggy Tennessee afternoon.
P.S. The heat dome responsible for these brutal high temperatures is finally moving on. Cooler, more normal weather is on the way over the next few days. The nightmare stretch should be just about over.
