How is data processed at each radar site weather services use?

Let's get technical.

By using data from the radar site weather forecasters can make quick forecasts.

They use computers to help them interpret the data retrieved by the radar equipment. How? You might ask...

They get a more complete convection picture, detect violent systems and update warnings when time is of the essence. But how do they make sense of these illustrations and radar system weather images?

After coming out of the radar site, signals are normally reflected by dense things in the air. Targets such as falling precipitation, airplanes, swarms of insects or birds and so forth.

We care mostly about precipitation which gives us these weather pictures. And radar processing systems have advanced algorithms to convert returned signal strength to precipitation intensity.

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A bit of math conversions.

The processor uses a few technical assumptions about the physical characteristics of the beam and the target(s).

Then a crude mathematical relationship translates reflectivity to precipitation rate.

The radar site weather conversion mathematics formula looks at the reflectivity. That is, ratio of reflected to broadcast signal.

Then the computer applies an exponential algorithm. The math used depends on whether we expect rain, hail or snow. But usually we raise it to a power between 1.5 and 2.5.

The reflectivity, given in decibels (dBZ), is the ratio of the incoming reflected power flux to the initial power sent out. Flux is power per unit area, the amount of energy passing through a certain area in a specified amount of time.

After that, the program multiplies by a scaling constant. Its value depends on a multitude of factors. Often, these formulae carry the names of the researchers who devised them, such as Marshall-Palmer and Srivastave. They are not deadly accurate, but useful nonetheless.

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Definition mathematics...

Here is a list of values used by the U.S. Government (NOAA) to convert radar site weather data to meaningful rainfall rates. 25 mm is about one inch.

One thing to note. An increase of 10 on ANY decibel scale, where the units start with dB means the intensity of the reflected radiation is TEN TIMES more powerful. That does not mean the storm is 10x stronger, just the incoming power.

What happens if there are two storms in a line? We call it attenuation. The closer cell makes it difficult, even impossible, for the storm chasers to see the further one clearly on the weather radar. See the example circled below.

Enhanced absorption and scattering here cause us to lose more power. In this case, the radar site weather information becomes reduced or even totally obscured. It's free to get monthly weather science articles.

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