Plenty of rain tomorrow and the strong southsouthwest gradient winds will enhance the orographic component of the rainfall drastically the further up the south wales valleys, the relatively high theta-w will make this worse.
Ground is already saturated in South Wales so much of the heavy rainfall will run off immediately across roads, and with saturated soil conditions small landslips are possible. Travelling in South Wales valleys tomorrow could get very fraught if all these things come together. We've already had a small landslip nr Chepstow tonight which has closed a railway line. Remember the Rugby in Cardiff tomorrow night to, so lots of people will be trying to get into Cardiff during rush hour instead of away from it.