On thing I have noticed (but cannot explain) is the occasional "blip" in the SNRM traces. For the higher of the two traces the blip goes upwards and for the lower of the two traces the blip goes downwards. Perhaps it is something that WWWombat may be able to explain . . .
Not exactly, sorry. Just add more mystery ...
When I zoom into MDWS, down to a couple of hours, I see that the upstream & downstream blips are actually separated by a minute. When one direction blips, the other is normal.
Looking at upstream alone, but looking at the 3 bands, you can see that U0 and U2 both are at low levels, but those levels are encountered regularly ... but just "chance" that both are low at the same time in this minute. U1, however, seems to take an irregular dip. The cumulative effect shows up.
Downstream alone shows a blip for both D1 and D2. Interestingly, there is a similar blip around 40 minutes earlier that isn't visible on the aggregate SNRM chart.
It makes me wonder just how volatile the line is ... and how it appears when sampled very frequently instead of once per minute.