ZCZC is the Start of Message signal for a few protocols, including NOAA's SAME, which seems relevant here as this is a NOAA broadcast. https://en.wikipedia.org/

ZCZC is the Start of Message signal for a few protocols, including NOAA's SAME, which seems relevant here as this is a NOAA broadcast. https://en.wikipedia.org/wiki/Specific_Area_Message_Encoding https://en.wikipedia.org/wiki/Specific_Area_Message_Encoding