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How radar works to detect storms and severe weather

ROCKFORD (WREX) — The weather radar network across the United States is a invaluable tool to help detect severe weather, let alone let you know when rain or snow is coming. Here's how this amazing tool works:

Radars send out microwaves that bounce off of raindrops, showing where they are.

Radar, which stands for RAdio Detection And Ranging, sends out burst of microwaves through the sky. This energy bounces off of small objects like raindrops, snowflakes, hailstones, and whatever else may be floating in the clouds. The radar detects the amount of energy bouncing back, and paints the colorful picture you see on your weather app or on the TV screen.

The brighter the radar image (the yellows, oranges, and reds), the heavier the rain showers.

Heavy rain shows up brighter on radar, as there are more raindrops within the cloud to send energy back.

Hail is extra reflective, which helps identify when a storm is going severe.

Hail shows up brightest, as the chunks of ice (relative to the smaller raindrops) are highly reflective and large. This is handy when trying to identify if a storm brings a hail threat or not.

As storms move, the radar can pick up on the change in the return beams. This helps identify the speed, direction, and rotation within the storm.

Radar can also detect the speed and direction of a storm using the doppler effect. Much like an ambulance siren changes pitch as it approaches then drive by you, the doppler effect can be picked up by radar. As a storm moves, the frequency of the microwaves returning to the radar dish change. The radar picks up on that change, leading to information on the storms speed and possible rotation.

Being able to see rotation in a storm helps speed up when warnings are issued for tonadoes.

Being able to spot rotation in a storm can be life-saving. Meteorologists can see rotation starting and warn people in the path of the storm before a tornado even reaches the ground. This also allows meteorologists to see where a tornado threat may be, even when observers on the ground can't. Rain-wrapped tornadoes or tornadoes at night are extremely difficult to see. The radar helps spots where the danger may be.

Dual-pol radars can help show where things like debris are in a dangerous storm.

Dual-polarization technology came on the scene about a decade ago, and adds to the tools meteorologists can use during storms. Dual-pol radars send out alternating horizontal and vertical beams. Changing the orientation of the microwave beams provides different scans of the objects in a storm. These scans allow meteorologists to see where precipitation may be freezing, speeding up the process of identifying hail. Since debris like tree limbs and pieces of a house are shaped differently than rain and hail, dual-pol radars pick up on those differences and can "paint" where debris is flying around. This identifies not only that a tornado is on the ground, but that it is producing damage. Warnings go out quicker when debris can be spotted.

Recently, the speed at which the radar scans the sky has improved. During active weather, radars can scan the entire sky in less than a minute. When a tornado can form in under a minute, having as much speed as possible to scan the tornado is key.

Radar continues to be a life-saving tool to get warnings out about severe weather. Without it, we have to wait until the storm is almost on top of us. By that point, it is too late to get to shelter. If you know storms are in the forecast, pay attention to the radar when outdoors. Move inside quickly if a storm is near. Stay tuned to the 13 Weather Authority for when storms are in the forecast. They likely will show the radar images to help track the storms!

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Alex Kirchner

Alex Kirchner is the Chief Meteorologist at 13 WREX. He joined the 13 Weather Authority in 2014. Alex earned Certified Broadcast Meteorologist recognition from the American Meteorological Society, and his work at WREX earned him a Best TV Weathercaster award from the Illinois Broadcasters Association and 2 regional Emmy awards.

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