12:31
@Emerson Late Jan is good if you like skiing/snowboarding, as the Highlands get most snow then, however it can be miserable and wet, so that can be hit or miss.
August is lovely - most sunshine, Edinburgh Festival (world's biggest comedy/culture/arts festival) but in the west the midges are at their greatest, and they can ruin your day on Skye or Islay if you aren't prepared
May-June - generally pretty nice, medium temps, not yet too many midges, not too great a chance of rain