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First off, I know that flying into actual icing conditions in an aircraft not equipped to handle icing is a Very Bad Idea ™ for any number of reasons. That's not what I am asking about here.

Rather, the situation I am asking about is where (for example) the low-level forecast indicates a possibility of or the existence of (particularly, light or moderate) icing conditions, while visual meteorological conditions prevail throughout the area of one's flight, and there are few or no clouds (scattered or clear) nearby.

In such conditions, is icing an actual concern?

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Well if you have a forecast of icing, and you go outside and the sky is clear, the forecast is wrong no?

In any case, when you are flying around VFR and there is the possibility of icing on your route, your main concern is the freezing level, and whether you can stay well below it in the event you encounter rain or drizzle or whatever (aside from visibility requirements of course). If you will find yourself close to or above the freezing level where you plan to cruise, you have to avoid visible moisture, period.

You're VFR so you will be avoiding cloud anyway, but if there is anything coming down out of the clouds you will pass through, you need to be a couple thousand feet below the freezing level to be safe.

So, if you're going from a to b, at 5000 ft, and the freezing level is 8000 ft, and there is light rain forecast with icing expected, say between 8000 and 15000ft, you're fine at 5000 ft IF, the freezing level is going to stay well above you on your route, but you need to be confident that temperatures aren't going to drop and force you lower part way there.

If the sky is clear or scattered, nice VFR in other words, you are unlikely to see icing in a forecast anyway.

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  • $\begingroup$ I have seen moderate icing mentioned in the LLF, yet been able to look out the window and barely see a cloud anywhere. The problem here is that even the relevant portion of the LLF covers a pretty large geographical area and IIRC up to FL100, far from all of it relevant to any one flight, and it seems to me that at least on occasion, someone has been hedging their bets by mentioning the possibility of moderate icing conditions (our LLF doesn't cover light icing at all) in what seems to be a larger than required area. My theory books offered little in terms of guidance, hence my question here. $\endgroup$ – user Apr 17 '19 at 6:15
  • $\begingroup$ Also (but not exclusively) given your mention of the freezing level, if the aircraft is equipped with an OAT sensor, keeping that well above freezing should also help, no? (Assuming for a second that it works properly...) $\endgroup$ – user Apr 17 '19 at 6:16
  • $\begingroup$ Yes you need to monitor that when flying in cool weather and there is any precipitation. You want at least a 5 deg C margin above freezing at an absolute minimum, and if inexperienced probably more like 10. When I was bushing flying I would do trips in late fall where it was raining and the freezing level was only a thousand feet AGL or so and I had to stay at 500 ft off the treetops because if I went much higher I'd start picking up ice. You do some crazy stuff while in the bush. $\endgroup$ – John K Apr 17 '19 at 21:10

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