What you see on radar isnt always what you get

radIf you were watching 13 news at 6 last night, you may have seen Jeannie and myself mention that it was raining here at the station even though the radar didn’t indicate it. Just as you may notice certain radio stations coming in more clearly depending on the weather, Doppler radar is subject to the same physics that alter our reception. When conditions are foggy as they were last night, we have what is known as an inversion (see: Inversion). In short, this is when warmer, less dense air is above colder, more dense air. When the beam from the radar is shot through this differential airmass, the waves travel ever so slightly faster through the warmer air than the cooler air near the ground. When the top of your beam propagates faster than the bottom, it curves down and doesn’t travel as far. The opposite can happen with a switch in warm and cold layers causing the beam to travel too high and not follow the curvature of the earth as well. The current vertical temperature situation is something that we as meteorologists try to keep in mind when we analyze radar and try to match up our screens to what is actually occurring at the ground.


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Posted under science

This post was written by qni_it on January 24, 2010

7 Comments so far

  1. WI Weather Buff January 24, 2010 10:21 PM

    Aaron, I love your little science lessons. Keep ’em coming!

    🙂

  2. tony January 24, 2010 10:33 PM

    I can concur with what aaron said. I know a few years ago, I was with my friend and we were in downtown rockford and there was low clouds and it rained pretty good. The radar didn’t even show the rain and adam painter said that it didn’t show up because the clouds were probably low and beam didn’t pick up the rain.

  3. mike January 24, 2010 10:52 PM

    inversions are never fun to fly small planes in.. you get worse performance as you go up in altitude!

  4. Aaron Brackett January 24, 2010 11:26 PM

    Thanks guys! Radar is something that has always interested me and I was fortunate enough to take a semester long class on Radar.

    Mike, I bet. As you very well know, engines lose horsepower at altitude because of less dense air, inversions work the same.

    -AB

  5. WI Weather Buff January 24, 2010 11:40 PM

    Geez, Aaron. I’d love to be able to take a semester long class on Radar. I’m so jealous!

  6. Aaron Brackett January 25, 2010 2:58 AM

    Honestly, some people thought it was boring, but I was fascinated by it. Our course book was great and was actually a pretty easy read. You can find it at http://www.radarwx.com/ if you’re interested.

  7. Adam Painter January 25, 2010 6:57 PM

    If I remember the saying correctly, Tony you have the memory of an elephant.

    As for that Sorensen character, tell him to take it easy on the Vikings fans in the area.

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