If we need an ALTERNATE, What is the use/meaning of TEMPO and visibility along the RWYs for?
you can legally file an alternate with a TEMPO forecast below your minimums but it may be a risk when you truly have to go there so calculate extra fuel when you have to hold over the alternate. on approach the RVR must be above landing minimums when you,re at the outer marker position. otherwise you have to abort from that position.
if RVR at the outer marker is in limits the final decision to land or go around is of course made at DH regardless what the metar says.
-I understand that we have visibility above the minimums (CAT IIIA) along the RWYs for Take-off and also for landing, havenīt we?
for CATIIIa you are well in the limits .
generally i must say i never saw a weather that lasts for more that a very short period which would exclude a landing with a CATIIIa aircraft and such trained crew.