If you are considering the Monk’s Trod, between Claerwen farm and Pont ar Elan via Carn Ricket (shown on the OS map as ‘Ancient Road’) go armed with a massive sense of humour. It is an exceptionally boggy mess, thigh deep in places for hundreds of metres. EVERY time I ride it I swear that I will NEVER do it again, it is that bad. Time dulls the pain and I forget just how bad it is… only to be reminded after it is too late. The very best time to visit it is after a long and extremely hard freezing spell.
I live further south in Carmarthenshire. Last weekend the hills above Llandovery were surprisingly dry but since then we have had a couple of days of rain.
The Elan Valley hills are seldom dry (hence the reason for building the reservoirs) so expect to get wet feet even in dry and sunny weather.