RVR is not forecast in a TAF. So you require your destination met. vis. to be forecast at or above your required visibility to depart with a single alternate. The only exception might be a very short flight (<10 minutes) that would be covered by the TREND in the RVR values contained in a METAR or SPECI report. But if you start getting as cute as this you should start asking yourself why. Also, don’t forget you can always start an approach but you may not descent below 1,000’ AAL unless you have the required RVR (or vis.).
PM