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My meteorology textbook (from Pooley's Air Pilot's Manual series) has a list of abbreviations used in met reports and forecasts. They include:

  • FG for "fog"
  • BCFG for "fog patches"
  • PRFG for "fog banks"

What's the difference between these three?

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  • $\begingroup$ @mins You might want to post that as an answer because it has all the info in it. $\endgroup$ – SMS von der Tann Dec 14 '15 at 20:01
  • $\begingroup$ @mins Very descriptive link, thank you. Let me know whether you're going to write that up as an answer; if you don't want the rep, I will do it myself. $\endgroup$ – Dan Hulme Dec 14 '15 at 21:21
  • $\begingroup$ @DanHulme: I won't write a full answer, so feel free to compose yours. Thanks for asking :-) $\endgroup$ – mins Dec 14 '15 at 21:25
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Thanks to mins's link, the Australian Government Bureau of Meteorology explains everything in detail. To summarise the particular part I was asking about:

  • FG on its own means fog (visibility < 1000 m) covers more than half of the horizon
  • PRFG and BCFG are fog covering less than half of the horizon
  • PRFG (fog bank) is more extensive than BCFG (fog patches)

Another way of looking at it is like cloud cover descriptors. FG is like BKN or OVC: more than half the horizon is covered. PRFG is SCT, and then BCFG is FEW.

All the above are used when the temperature is above freezing point and the fog reaches more than 2 metres above ground. If the fog is only below 2 metres agl, it's shallow fog MIFG instead. If the temperature is below freezing, so the fog consists of supercooled water droplets, it's freezing fog FZFG.

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  • $\begingroup$ Sounds like Eskimos and all their words for snow! $\endgroup$ – FreeMan Dec 15 '15 at 18:29
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  • BCFG is patches of fog (BC = BanCs, French origin)
  • PRFG is partial fog, meaning that part of the aerodrome is covered in fog, but the coverage is not extensive enough to qualify as fog (FG).
  • VCFG is fog in the vicinity of, but not on the airport
  • MIFG is shallow fog (MI = mince, French origin)
  • FZFG is freezing fog
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