That's odd.  The only TV connection those call letters have to TV is as channel 17 in Buffalo for 5 years in the 1950's.

Both WBUF and WTSS are local primary (LP) stations for the EAS system in the Buffalo area. (It's WPXY and WHAM for Rochester.)

The way the US system works, each state is required to have its own EAS plan that designates regions and monitoring assignments. State and local emergency agencies originate the content of emergency messages and the system then disseminates those messages outward starting with the LP stations. Every other station in the region is then required to have an off-air receiver monitoring the LP stations to pick up and rebroadcast those emergency messages.

The LP stations must each originate a required weekly test (RWT), and that's what you saw on TV. It's done during daytime and nighttime hours on alternating weeks. Including the source at the end of the message allows the engineer at the downstream stations to log where it was received from and make sure the system is working properly.

There's also a national component to the system, with a smaller number of stations designated as presidential entry points (PEP), with hardened facilities and direct connections to DC. National emergency messages would flow through those PEP stations to the LP stations to the rest of us.

If this all sounds a little ungainly compared to just contracting with Pelmorex to deliver to everyone, it is! The US system is increasingly moving to using that over the air daisy chain as a backup. The main distribution of emergency messages is now through a computer system called CAP.

Even so, every licensed radio and TV station (translators don't count) in the US must have an "EAS box" that is connected to receivers tuned to the LP stations as well as to the CAP internet feed. And they must retransmit those weekly tests. That's what you saw on WGRZ - a test that was scheduled from WBUF being picked up and rebroadcast.

There's a time window during which the rebroadcast of that test can be delayed (I want to say 30 minutes), but it appears WGRZ just had their EAS box set to immediately retransmit regardless of what was on the air being interrupted.

Other than a presidential national activation, rebroadcasting any other level of alert is optional. Most of us at smaller stations set ours to rebroadcast major weather categories like tornado warnings and flash flood warnings, but not lower level advisories like winter storm watches, which are too frequent around here.

Thanks for the kind words!

It's not new - the system goes back to the 1990s - but usually the required tests are scheduled at less disruptive times. I tend to see the daytime ones in the  10 AM hour here.