Even the Weather Radar Beam is Effected

[RandyB]

--July 17th--

Looks like a pretty classic VHF/UHF propagation event unfolding across portions of the Midwest. Noticed the attached image--even the weather radar beam is being affected by the low-level temperature inversion that has developed in the wake of a complex of thunderstorms that moved across Illinois and eastern Missouri late this morning through early this afternoon. I suspect that there's some pretty good VHF/UHF ducting going on in this area.

 

[DaveNF2G]

Just out of curiosity, how did you identify the imagery as being anomalous?

 

[RandyB]

It can be difficult to tell. Genearlly, anomalous propagation signals will either be stationary or randomly dance around--not really matching what you would expect for storm motion. That can be the first clue. Also, with a thunderstorm, you expect depth. So, you could look at higher tilts to check for depth. In this case, depth was not present. Consider that the beam hits the inversion layer and is then directed back down to the ground before being reflected back to the radar. If you change the tilt of the beam, it throws everything off. The AP will not show up in the same location and thus no depth will be seen. Those are the two main ways to tell. Sometimes it is pretty tricky and you must have a good knowledge of meteorology and the environment you're dealing with that day. The radar often times does a reasonably good job at throwing this bad data out. However, in extreme cases like this example, the radar may have a tough time doing so.

After I posted this, it continued for a while. I'm surprised that nobody has posted from this area saying that they were receiving distant VHF/UHF signals. If a 10 cm wavelength signal is being impacted by the weather conditions, UHF and VHF should as well.

 

[Dispatrick]

wow

this my explain why i was pickin up a lot of Noaa stations from PA early this morning before a severe storm (I guess that one) passed over my area from about the south west!

 

[RandyB]

Take a look at this from about a month ago, too:

http://www.radioreference.com/forums/showthread.php?t=72253

 

[nascarfan999]

I am in the area affected that day, but unfortunately I was stuck at work during the day.