I agree, the forecast looks like it has potential for plentiful midges on the eastern edges.
Your best options are:
- Limestone - Peak midges are very snobby about rocktype and generally don't go near the lime.
- High moorland grit - The predicted windspeeds at higher levels look strong enough to stop the midges. Just make sure you pick an exposed crag, not in the lee of the hill.
- Lowland grit - Some grit crag, in pastural surroundings rather than moorland are less prone to midges. E.g. Black Rocks, Cratcliffe, the Amber Valley, or Churnet (yes I know some Churnet crags are not grit).
Internet suggested that "Avon Skin So Soft" doubles up as an effective and not too expensive midge repellent at £3.50 a bottle. So I took a punt on it for a trip to Ogwen Valley last weekend, and after the first three minutes was surprised to discover it actually worked.
Also you smell of Jojoba right up until a first pitch of climbing ruins the effect.