Anomalous Propagation and Visible River Paths In Response To Advancing Outflow BoundaryJR Hehnly | February 28, 2009
Here’s a radar question that’s been bugging me for a couple of years. I have noticed that sometimes, as an outflow boundary approaches a radar site, the amount of anomalous propagation increases the closer the boundary gets to the radar. Interestingly, once the boundary passes over the radar location, all of the AP goes away.
The best example I’ve seen is from the evening of August 30, 2008. As an outflow boundary approached KTLX from the northeast the AP increased significantly in most all areas around the radar, but was greatest to the south and southeast of the radar. On thing I noticed, though, was that the AP was mostly absent along the path of the South Canadian River at the southern borders of Cleveland and Pottawatomie counties.
I have two questions on this. What is the process causing the AP to increase as an outflow boundary approaches, particularly in directions opposite the boundary? Also, what process causes the absence of AP along river paths? Is it just the lower elevation associated with river valleys, or is there some other cause that is unique to a river?
If you want to view the August 30, 2008 event using your own software, the raw Level-II files (150 mb) are located here.
Here’s a java animation consisting of 40 radar frames from the event. Use the slider at the top to advance the frames and see the changes as the OFB approaches.