Hi there, as NellieTheChefelant said above, Tropospheric Ducting conditions, bringing in continental signals

A good Indication of this, is to listen to the FM Band Well Below 88megs.... (as mostly only Legit RSL and pirates here)
If really good Tropo, you may even see Continental RDS station names come up in UK.... before DAB is affected,
because DAB is around Twice the frequency of FM band. and as its Digital, you wont actually hear the interference

Trouble is, It comes down at high angles, from different layers of warm and colder air, which bends signal paths
Really good tropo, can even wipe out UHF freeview TV

Rod Watts