On hearing that Andy Clark had found a male Subalpine Warbler on his local patch at Mynydd Mawr near Uwchmynydd yesterday I took the afternoon off and headed down there and met up with Eddie and Andy. The bird was favouring the north-western fenceline of a square sheepfield on the left hand side of the track up to Mynydd Mawr - there's a large open grassy area for parking.
The bird showed well all afternoon as it fed in the brambles and gorse along the fenceline, occasionally venturing onto the path and grassy slope. The pink throat and chest extending diffusely down onto the belly and flanks indicated that the bird is of Western origin (cantillans) as did the dry tacking call and the song, which it gave a few times over the afternoon. I've added a few phone-scoped pictures below - I'm sure there'll be better ones to come soon!
The bird was still there today, with the added bonus of a male Woodchat Shrike just up the road near Aberdaron.