Hey DaVikes,
It is really hard to say based on your screenshots (due to only have about 30 second samples), but it *does* look like this is on Comcast's side.
It *does* look pretty similar to bandwidth saturation (as seen here:
http://www.pingplotter.com/commonnetworkproblems/#bandwidthsat). At this point, it may prove helpful to continue monitoring for a longer period of time (if you could let PingPlotter run continuously for 24 hours - that would be great). This would allow you to see if the pattern here happens to be time based (do the spikes in latency/packet loss drop during non-peak hours - when no one is using the internet?), which may help provide more clues to what is happening here.
We do also have a great guide to troubleshooting network issues that you may find useful here:
http://www.pingplotter.com/netnirvana/If it is shown to be Comcast's network, this guide will show you how you can prove it to them by building a good case.
Hopefully, that will point you in the right direction to start solving this. Please let us know what happens with a longer monitored timeframe.
Cheers!
-Phillip