"oneatcer" wrote in message
...
My book say PIREPs are acceptable for the fact that I have to disseminate
them. Controllers can make a ground vis report. AWOS/ASOS is ground vis.
METARs 45 minutes old will suffice due to the requirements of issuing a
new
METAR when the vis changes by a reportable value. And if my memory serves
me right, that is +/- 1/4 mile when it gets down around 1 mile.

It is interesting: A USA weather service observing manual:
http://www.srh.noaa.gov/ohx/dad/sfc/chapter9.pdf
only specify visibility crossing 3, 2, and 1 miles, plus the lowest
published limit.

In the Canadian rules, the requirement was crossing 3, 1.5, 1, and .5 miles.
Also, crossing 3/4 and 1/4 mile was a requirement when the airport has
precision approach equipment. (Not sure how that relates to published GPS
approaches... not an IFR guru.)

In either case, once the visibility falls below the lowest published minimum
(the airport is effectively closed), no special METAR need be issued until
the visibility rises back up above that minimum.

This means that mountain airports with relatively "high" minimums.... such
as The Dalles, Oregon.... once the METAR was issued showing visibility below
1.25 miles.... there need not be any special METARS issued, (even if it
goes to zero as I understand it)... until it gets back up above 1.25.