Re: LHR "grooved" Runway?!
Quite often at LHR when the weather is "wet" the runway is visibly dry. I have taxied out on wet taxiways a number of times to find a dry runway. This might also be a function of the number of movements as well as the surface. I still use wet take off performance when we request the figures - although in practice it makes no difference unless a reverser is locked out or the runway is short - at least for us.