Netblocks is reporting connectivity in New Orleans LA is at 72% of normal as Hurricane Ida makes landfall.
There are per-incident things, like the outages mailing list and downdetector.com. And some academic outage discovery projects such as RIPE, IODA, etc.
The old outage dashboards seem to have been bought, merged and disappeared.
What is your preferred long-term Internet outage tracking source?
Depends on the type of outage, as that depends on what part of the Internet is critical for you. (eg. if google goes down, personally, I really cannot care, except for friendly SREs getting no rest; but lots of people will mind 
)
For webpages or ISP there is as you noticed, depending on country from downdetector:
https://allestoringen.nl
https://allestörungen.ch
https://allestörungen.at
which gives a decent good overview, especially as it seems they seem to check what people are searching for and guess that when people search for it that things should be down.
As this is a Q on NANOG though, if you are looking at ISPs, participants of NLNOG Ring (https://ring.nlnog.net) have access to RING SQA (RING SQA - NLNOG RING) that will inform one of outages as seen from a RING node along with traceroutes to the targets that are unreachable for your node.
Thus join NLNOG Ring and get free monitoring 
The last one that is useful is of course RIPE Atlas, and with software probes and anchors it is very easy to join, and the measurements one can do with that are very customizable. As usual: depends on what you care about on the Internet...
Greets,
Jeroen
Netblocks is reporting connectivity in New Orleans LA is at 72% of normal as Hurricane Ida makes landfall.
https://twitter.com/netblocks/status/1432038858460442625
There are per-incident things, like the outages mailing list and downdetector.com. And some academic outage discovery projects such as RIPE, IODA,
IODA near-realtime dashboard tracking Louisiana:
https://ioda.caida.org/ioda/dashboard#view=inspect&entity=region/4430&lastView=overview&from=-2d&until=now
Best,
Alberto
self promotion for $DAYJOB: Another academic project from the Analysis
of Network Traffic (ANT) group at University of Southern California's
Information Sciences Institute. Here is a link that will playback Ida
making landfall at 1x, 2x or 4x speed.