The 1680 signals have been on for several years now. I believe there are several transmitters in different parts of the city. One is near the Katy Freeway and Washington, presumably at the Transtar building on Old Katy Road.
The NOAA Weather Radio on Memorial Day might have been filler for the holiday. Usually has traffic advisories.
The 1680 signal at night is clobbered by all the X-band broadcasters on the frequency, so you have to be within a couple of miles of one of the transmitters to hear them clearly. The signals do much better in the daytime, heard throughout the metro area.
Supposedly 1710 is available as a TIS/HAR frequency, but no one is operating there yet, other than a few pirates. The FCC needs to start moving the TIS/HAR stations there; every modern radio is able to tune it.