Originally Posted by Adlerdriver

Typically, the lower the vis, the more RVRs values are reported. They can be put into METAR format in ATIS and I haven't seen one particular standard. It can be as simple as "RVR 500/700/300" (with the first being TDZ, then MID and RO). When the weather is down to CAT-3 (or even CAT-2) minimums and 2-3 RVR values are required and being reported, they are usually being reported verbally by the Tower. The reports can be provided as often as every 10-15 seconds and rarely go longer than a minute without an update. This is due to the fact that reports below minimums on CAT-3 approaches even after established on final require a go-around prior to alert height. It's not realistic to expect a crew on an approach to be constantly checking ATIS for new RVR information that could be changing rapidly.

Correct on both statements.