Are discontinuities due to outages?

I often see very continuous curves of traffic, as reflected in the SiteMeter and IndexTools bar charts for the day. In this IndexTools bar chart for the NSFW blog "Former Naval Person", the discontinuities certainly seem to be caused by outages. The traffic curve for the day usually incrementally changes during the day. Depending on what is happening, the traffic will peak and then slowly decline. Often, oddly enough, there may be a rise late in the day, only to drop off in the early morning. At 2am, which is midnight, Pacific Daylight Time (Google?), there is a percipitous drop to a low level. At the 5am hour and again at the noon hour, there are drops that are discontinuous with the traffic before and after those hours. So what is happening? Interestingly enough, there was very little traffic for the first 1/2 hour of the 12 o'clock hour. The last part of the hour was very high traffic, as if the hour would have been much higher, but for an outage, early in the hour.