Today has been an active weather day with a lot of cool opportunities to explain how our atmosphere works. You can read a write up of why the freezing drizzle was such an issue earlier here.
Behind the drizzle was a quick-moving cold front that swung through the area in the late morning and early afternoon. These cold fronts are denoted by a blue line with blue triangles on weather maps but today, the cold front showed up in the satellite imagery, kind of - no blue lines needed!
Here is a loop of the visible satellite:
The surface cold front at 10:30 AM was positioned approximately where the blue line is drawn. The black line is most likely a reflection of the cold front slightly higher up in the atmosphere at the cloud level. Typically, systems will tilt to the west with height. The black line is actually a shadow cast by cloud cover ahead of the elevated cold front that is *slightly* higher than cloud cover behind it.
Both areas of cloud cover are roughly the same height (with a subtle difference) as we can see in the "longwave IR imagery" with the colors remaining the same across the elevated cold front.
It shows up in the "day cloud phase" product as well.