I guess they are using the Chroma key to make it easier to see the weather on tv. It does help since the video wall isn't very bright anymore, not saying it ever was.
Between the video wall having a blue tint, having the brightness go funky live on air, having the video wall backlights get darker and darker, the video wall borders (all having died at some point in time), having the center panel die at one point, I could go on, I'm surprised they're still using it for weather presentations. Just my opinion.
However, I will admit. I'm glad they're being smart about it and windowboxing their graphics on the chromakey as most of their graphics are not 4:3 safe.
EDIT [9:14am]: it seems Kelly Cass has acknowledged it, and her vague wording makes me believe this seems to be a longer term solution, as the video wall is still being used for non-weather presenting... It's like a major news network! lol ... link to facebook post
I noticed her post, too. I like the chromakey better than the video wall. A lot easier to see the graphics, and some of the OCM's don't seem so small on the chroma /
I saw the video wall being used on WC last night, and they were showing an "Arizona Tornadoes" graphic, but the "na" at the end of "Arizona" and the "es" in "Tornadoes" was cut off.