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?

-Nathan