What time zone are the turbulence maps for the USA? (VT vs UTC)


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I'm hoping someone can answer I question I've had for ages. Some of the turbulence maps are marked UTC, which I understand is Greenwich Mean Time, aka the time in London, e.g. Others are marked VT. Is that the same as UTC or different?

I ask because when I'm looking at a USA turbulence map and it says 800 VT, I don't know if that's 8 AM Pacific Time, 8 AM Eastern Time, or (I think?) 8 AM in London, which means 3 AM Easter Time and Midnight Pacific Time.

Since the maps change quite a bit over a 3 - 5 hour window, it would really help me to forecast my own flights to understand the time zone. And googling "VT time zone" doesn't help. :)