The missing RADAR echoes of December 25, 2009



What happened

On December 25, 2009, a 6-cm snowfall hit Winnipeg, Manitoba. There was not much unusual about this snowfall except for the fact that some RADAR echoes were missing and it looked rather suspicious.

First off, you see the snow on the 1 km CAPPI. Nothing out of the ordinary here:
1 km CAPPI

Then you look at the 0.1 degree PPI, and notice some of the echoes missing over the southeastern part of Winnipeg:
0.1° PPI reflectivity

The Doppler velocities at the time looked like this:
0.1° PPI velocity

So the question is: why did the LOLAA show a NE-SW oriented patch of no echoes over southeast Winnipeg? There are currently 2 hypotheses:
  1. That there was a pretty good shear zone in the area at that altitude such that the spectrum width was so high that the information was thrown out at the source
  2. That we're looking at second-trip echoes and the processor couldn't decide where the echoes actually were, and thus threw out the information

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Last update to this page: January 5, 2010