one of the many, many beautiful things about british limestone, is that there's always something in perfect nick:
Jan: minus 10 (always dry, conditions in inverse relationship with temperature)
Feb: rubicon (bring your wellies)
march: malham, rubicon, parts of the tor
april: as above (tor ought to be dry) plus kilnsey (hampered mainly by cold, north buttress often wet), cheedale starting to dry out (in an average year), high tor (cold if windy)
may: malham (on a cold/cloudy day), kilnsey, cheedale generally (cornice if you're lucky).
june, july, august: kilnsey, gordale, water cum jolly, cheedale cornice
september onwards: rewind the above.
don't forget that peak crags can suffer with condensation if a warm, wet air mass comes in following a period of cold, dry weather.
this is a very general overview. and only my opinion. and only of the major crags. for example malham can be boiling in february, freezing in may. anywhere can be wet or dry at any time of year.