Weathered Questions 5.7

And today's first question comes in from Derek.

And he asks, he says, I've heard meteorologists look at a radar image and say it's not actually reaching the ground.

How do you know?

Well, that's a great question.

In theory, if the meteorologist is saying that one way or the other, hopefully they've looked at least at a few things.

Number one, they look at the airport observations to see if we've had any ground truth reports.

or anything that's occurred near the ground.

Because what happens is as you go away from a radar, you pick stuff up higher up in the atmosphere.

It's two reasons.

Number one, the beam is actually tilted from the radar site.

So it goes up at about a half degree tilt.

And so over time, the beam goes higher, but also the earth is curved.

And so as you get farther away from the radar site, it curves away from you.

So you might be five or 6,000 feet off the ground by the time you see that radar detection.

And if there's a shower up there, Those little raindrops have to fall all the way through a mile of air.

If that air is really dry, we can use it by looking at some of the weather balloon data and seeing how big is my spread between my air temperature and my dew point, which we talked all about last episode

again.

So if you need to hit rewind and hit 5.6, we talk about dew point again.

But a large spread in that, we actually call that a dew point depression.

And the larger that spread, the drier the surface air is, meaning it's kind of like if you were to stand on a footstool and take a really fine spray bottle of water and just spritz it.

See if any of those little drops hit the ground.

In the wintertime, I bet you they don't.

A lot of them evaporate before they get to your kitchen floor.

Same thing in the atmosphere.

If you've got something maintaining it, though, then those drops will make it down to the ground.