Hi Stuart,
> That might be worth thinking about, though I suspect it would be
> rather laborious to do so using property rules.
Well, I did start this in Nasal, but Torsten converted it (incorrectly so it
seems; but that's not solely his fault) to property rules... :-)
> My main issue with it is that it can result in the snow level moving during a
> cross-country flight. Some time last year, when there was some snow in
> Scotland, I found it quite distracting as the snow appear then disappeared
> seemingly at random as I was flying, depending on whether the nearest
> airport was reporting snow in their METAR or not.
That sounds like it was caused by the bug I fixed today. Snow should not
dissapear (except when you fly over some terrain with lower elevation of
course). The snow level can only get lowered due to a METAR station reporting
snow at a lower elevation. The system never increases the altitude of the snow
line. The snow line does not change if a METAR station reports no snow
(actually "if there is no report of snow"). It simply stays where it was.
When you fly into the range of a new METAR station that reports snow at a lower
altitude, then you will suddenly see snow appear at lower elevations (might be
nice to add some time filter for that actually, so it gradually lowers). When
you fly into the range of another station, the snow level will stay the same,
or lower even more. But it will never get highered.
You are right that the behaviour I describe here was not seen up to today. The
snow line was really buggy before I commited today's fix, so please try it
again. I think you've got a needlessly bad impression of the system.
> Fundamentally, I don't think that the METAR information provides a good
> enough proxy for the snow level.
METAR can only report snow. It cannot report the absence of snow. And most
stations don't even report snow in the METAR (you've got SNOWTAMs for that;
where they give info like snowdepths and braking conditions for each runway).
So yes, it is only right in very few cases, but that's why I designed the
system the way it is (supposed to be).
The system only comes in action when there is a pretty good reason to believe
there is snow. In any other condition; nothing is done.
Cheers,
Gijs
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