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3 Answers

VFR on top…..where are the tops?

Asked by: 2487 views , ,
General Aviation, Instrument Rating

I understand the VFR On Top clearance, requirements, and how it works, but my question is how to determine the height of the cloud tops. I know they are occasionaly reported in PIREPs, but is there any other way to find this information?

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3 Answers

  1. Jonathan Silva on Jul 12, 2012

    Off the top of my head, I don’t believe so. I would only consider VFR on top as an option for someone with an instrument rating, just because the probability of being able to get back down VFR is sometimes slim to nil.

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  2. Bob Watson on Jul 18, 2012

    I get these confused all the time (and I had to look them up, again, before commenting).
    “VFR on top” is an IFR clearance where you climb through a cloud layer to a VFR altitude above the clould deck.
    “VFR over the top” is the VFR operation (not a clearance) that Jonathan described (and is of questionable judgement…How can you navigate by visual reference when your only visual reference is the blue sky and a cloud deck that may or may not be parallel with the horizon?)
    In practice, you’d probably get the tops from recent flights (e.g. airliners) that have already punched through the cloud deck and reported the tops back to ATC. Here in the Seattle area, however, they are pretty predictable. We tend to have: a) clear skies (occassionally. really, we do 🙂 ), b) high tops (20,000+ when we get an on-shore flow), and c) low tops (3-5000 MSL, when we have our usual marine layer). PIREPS will confirm or correct those assumptions, but after you’ve watched the clouds for a while, you start to see some patterns.

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  3. Bobby Roe on Dec 16, 2012

    One reasonable source of cloud tops data is the RUC Soundings tool and looking for the split between the temperature and dew point lines as the altitude increases. There’s a tutorial link on the page listed.

    One other thing about the RUC Soundings tool that I find extremely helpful is that you can use it to find a relatively turbulence-free layer on an otherwise uncomfortable day. There have been several days I was able to climb through a couple thousand feet of bumps to get a glass-smooth ride that I wouldn’t have known was there without the RUC Soundings.

    – Bobby

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