In reply to 1philjones1: I met a climber today who had climbed Central Trinity yesterday. He said that there was a lot of graupel (snow, like polystyrene pellets) which often forms a persistent weak layer in the snow pack, and whilst there was some firm neve, the snow had insulated the underlying turf so it was not frozen. I had a nasty experience soloing Cave Gully in those conditions (it was marginally less dangerous to climb than to retreat) and wouldn't recommend it to a friend.
The BMC Cwm Idwal temperature sensors seem to be an accurate guide to ground conditions on the high, north facing crags. If that doesn't report a solid freeze at 5cm depth, then gullies are unlikely to be in condition in Cwm Idwal, Clogwyn Du and the Trinity Face.
Routes on Clogwyn Du today that didn't need frozen turf were ok, but dripping wet. To test the accuracy of the sensor I tried an experimental placement in a turf blob and it pulled right through - just as predicted. climbing on un-frozen turf will be dangerous, ruin the route and could result in a climbing ban by Natural Resources Wales for damaging a Site of Special Scientific Interest.
You can view the temperature sensor read-out here:
https://www.thebmc.co.uk/idwal