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?
Thanks to mins's link, the Australian Government Bureau of Meteorology explains everything in detail. To summarise the particular part I was asking about:
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.