"Ben Hallert" wrote in message
oups.com...
It's not a conspiracy of mediocrity, it's due to a technical limitation
of the scatterometer technology used by ASOS's to determine visibility,
if I recall correctly. They can only really be accurate out to about 6
miles. A human with a Mark I Eyeball could pick a landmark furthre
away and provide a bigger distance, but for all intents and purposes,
the max visibility will be defined by the technical limitations of the
available data sources.

The short answer to the OP question is: YES!

This is not so much due to a "technical limitation", as it is due to
*history*.

The requirements forever (well, at least since the 1950's), have been that
.... no restriction to visibility is reported, whenever the visibility is
more than 6 statute miles... In other words, an observation may *not* read
7 miles in haze, or 7 miles in mist, etc. *Precipitation* may be reported
at visibilities greater than 6, but you do not report
non-precipitation-phenomena by itself. You would just report "visibility 7
statute miles", period.

Thus, a visibility above 6 statute miles, as per the technical requirement
of observing weather, is "not obstructed".

Now, in general, when you had manned systems, airports attempted to have
visibility markers out to *at least* 15 statute miles, and a report of 15
was the norm for "unrestricted" visibility. Thus, you kind of knew that
something was going on, should that station suddenly report "10", or "8",
even if he did *not* show the reason.

However, with the increasing advent of automated systems, you have lost that
extra human insight, because the technical requirement is met by saying....
"greater than 6" equals "not obstructed"..... so you might get "greater than
6" on a day when visibility is 50, and from the same station you get
"greater than 6", when visibility is 7.

In that sense, I *DO* say that it *is* a conspiracy of mediocrity. To
automate things, and to meet only the basic requirements of producing a
METAR... a lot of the stringent reporting practices of the 60's and 70's
seem to be slipping away.