"Nathan Young" wrote in message
...

KPIA 151254Z 02004KT 10SM R13/3500VP6000FT CLR
09/06 A3029 RMK AO2 SLP259 T00890061

How can it be clear and 10SM, with a RVR of 3500-6000feet?

Is the 10SM measured from the tower cab, and the RVR at
the runway?
Perhaps a thin layer of fog?


It's an automated observation. The surface visibility is taken at the ASOS
site, wherever that is on the field, and the RVR is taken along the approach
end of runway 13. They could be a couple of miles apart.