Another helpful test is to take a handful of hay and wring it tightly - if there is the least bit of soggytude there then it's not quite ready - it should be totally crisp. Try in many places, and take samples from the underside of the windrows as well as the top. If the ground or air is damp, your hay will not be baleable. Our neighbour told us always to leave it another day if you possibly can once you think it's ready, just to be sure. Also stook the bales (stand them on their ends two together in an upsidedown V) before stacking to reduce the chance they will heat up, and leave air channels between the stacked bales. All this depends on perfect weather of course.