As of 06:24 US Eastern the appears to no longer be true. There is a NOTAM outage but no full ground stop is mentioned, just a few specific due to weather.
Edit: obviously a developing situation, see responses to this comment for current advisories.
Edit: obviously a developing situation, see responses to this comment for current advisories.
Edit: Of course as I was typing that, Advisory 028 pops up with a nationwide ground stop until 9:30 Eastern: "GROUND STOP ALL FLIGHTS / ALL DESTINATIONS EXCLUDES MILITARY AC AND MEDEVAC FLIGHTS"
https://www.fly.faa.gov/adv/adv_otherdis.jsp?advn=28&adv_dat...
Clearly still developing; we'll see.
At 5:40am Eastern, the agent at my departure gate told us that there was a ground stop affecting all flights, which was reflected in my original title. This was not reflected in the NOTAM I posted, as was pointed out by several early commenters, and in fact my flight was able to board and depart around 7:00am Eastern before the ground stop took effect.