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Weather forecasting would be nearly impossible without radar

Radar image from Louisville.
National Weather Service

You often see meteorologists referencing radar when they talk about the day's or week's weather, but do you know how essential it is to their work?

Every week WAVE 3 Meteorologist Tawana Andrew breaks down what we know and what we don't about the climate and weather here in Louisville. Read or listen to the conversation below about how radar technology is at the center of her work.

This transcript was lightly edited for clarity.

Bill Burton: It's time for us to take a look at the Science Behind the Forecast as I am joined by WAVE 3 meteorologist Tawana Andrew. Good morning Tawana.

Tawana Andrew: Good morning. We're talking about something that is fundamental to the forecast, especially if there's anything falling from the sky.

BB: Absolutely. I can't imagine how you would do your job without it. And our topic today is radar. Tell us about it. What do we need to know about radar?

TA: Basically, it works by sending a beam of radio waves from an antenna. And as that radio wave hits a various objects in our atmosphere, it's scattered and then returned back to the radar. It's the scattering that's allowing us to see the precipitation or anything else that may be hovering in our skies.

Now, meteorologists will measure the time it takes for a radio wave to be transmitted, and then returned to determine how far away an object is from the radar, and how and where it's moving in relation to the radar. So for an object's movement, whether it's away or towards the radar, it's calculated by measuring the change or what's called the shift and phase between the broadcasted beam and the received echo.

Positive phase shift indicates that the object is moving towards the radar and a negative phase shift shows that there's movement away from the radar. And the National Weather Service's Doppler radar antenna basically, automatically rises higher in Preset increments, as it rotates.

This is called an elevation slice. And these elevation slices create what's called a volume coverage pattern. Yeah, I know a lot of technical jargon here. So the radar basically completes a volume scan every four to six minutes. And keep in mind, within each hour of the day, the radar does not spend that much time actually transmitting pulses, it's actually spends a little bit more than seven seconds, each hour transmitting pulses. And then the rest of the time is basically spent listening for returns. It's really just listening. It's very good listener.

And for those who didn't know, radar was initially developed for military use in the 1930s. It was super vital in World War II. And then throughout the years, we started to get some upgrades.

In the early and mid 1990s, the National Weather Service installed a bunch of NEXRAD Doppler radars at major airports across the United States. This was a huge upgrade because it allowed us to improve severe weather warnings, because we could actually see the storms in a lot more detail and detect them more easily.

Between 2011 and 2013, the National Weather Service radars got another upgrade. And this was dual polarization. So this required a hardware attachment to the radar dish and some new software. And this basically gave us a much more comprehensive, two dimensional image of precipitation. So instead of just the normal horizontal pulses that we've been used to, we get horizontal and vertical pulses sent out by the radar. And this allows us to tell the difference between rain, snow, hail, we can even see where the rain is transitioning to snow.

BB: Now we have a much better understanding of just how critical it is for a meteorologist to have access to radar. And what radar does.

This transcript was lightly edited for clarity.

Bill Burton is the Morning Edition host for LPM. Email Bill at bburton@lpm.org.

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