The best way to get a definitive answer is likely to email the FAA (there's a link at the bottom of the AIP page) but my strong suspicion is that both RW and Venule are errors caused by scanning in an old document, or maybe manually entering it.
First, if you go back to a 2002 version of the FAA's ATC orders 7110.65, there are references to "RVR/RVV" values. I suspect that "RVV" was scanned or manually entered at some point as "RW" and no ever noticed. In fact, if you search the FAA site for "RVR/RW", the only hits appear to be old, scanned copies of paper documents.
I also found an explanation that shows that RVR and RVV were often used together, which to me supports the idea that "RVV" is the correct abbreviation:
- Provide RVR/RVV information by stating the runway, “visual range” or “visibility value,” as appropriate, and the indicated value. The
abbreviations “R-V-R” or “R-V-V” may be spoken in lieu of “visual
range” or “visibility value.”
The latest 7110.65 doesn't refer to RVV any more, by the way:
This changes [sic] removes all references to Runway Visual Value (RVV)
from this order.
Second, "Venule". Based on the dictionary definition and Googling, it's clearly a medical term, not an aviation or meteorological one. So what might it have been? The PC/G definition from the old 7110.65 linked above says:
Runway Visibility Value (RVV)- The visibility determined for a
particular runway by a transmissometer. A meter provides a continuous
indication of the visibility (reported in miles or fractions of miles)
for the runway. RVV is used in lieu of prevailing visibility in
determining minimums for a particular runway.
I can't think of a word close to "Venule" that means "in miles or fractions of miles" but possibly the original text was "1/4 mile increments" or "¼ mile increments" (or another fraction). Depending on the original text size, font etc. it's possible that "1/4 mile" become "Venule".
Anyway, this is all speculative even though I think it's very plausible. I'd definitely email them if you want an authoritative answer.