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Louisville is facing another day with the heat index predicted to rise above 100 degrees. It’s not just summer–it’s a high pressure system.

As part of a new weekly segment, WFPL Morning Edition host Bill Burton takes a look at the science behind the weather with WAVE 3 Meteorologist Tawana Andrew. Listen to their conversation in the player above.

WAVE3

Tawana Andrew

So, it’s hot because of a high pressure system. What exactly does that mean?

“It’s an area of higher pressure in the atmosphere. So usually, if you remember from your eighth grade science class, air flows usually from high to low pressure. So that kind of helps build that high pressure system over, right now, us.”

How does that affect the temperature?

“Let’s just think of it as a funnel through the atmosphere. You have at the upper levels, the air coming down, and the lower levels in the high pressure system, it’s pushing out. So what happens with the air as it does that? Think of it basically as a box of air. And as it pushes down, the volume decreases, because there’s more pressure on it and as that happens, the temperature increases. So you have all this air getting warmer and it’s drying out, so we see these clearer skies. That means more sunshine and unfortunately, hotter temperatures.”

Usually these high pressure systems hang around for awhile. What makes them stay so long?

“Basically how the atmosphere is moving at that time. Sometimes if it’s strong enough, the high pressure will take over and nothing can make it budge. Sometimes it’s a little bit weaker and you have let’s say an upper level trough that is going to push through and help nudge it out a little bit, which will thankfully happen this weekend. And that will cool things down and we’ll finally get a little bit of moisture, a little bit of rain back in our forecast.”