Hail - not always visible!
Geriaviator, ref your #10672 a hazard of hail is its invisibility unless falling fairly heavily, while the size of the stones is not necessarily related to the intensity of the fall; this was brought home to me many years ago dodging storms over Cyrenaica while en route Fayid-Malta.
Flying in clear air beneath a cb's overhanging anvil we were startled by a sound similar to intermittent (and loud) pistol shots, followed in short order by a couple of star-shaped cracks appearing on my windscreen. Fingering one of them, I was somewhat alarmed to find I could push the glass outwards and then feel it come back again as I released it. Given that the York's windscreen frame was of wood construction and thus unlikely to cope with the panel's complete disintegration, I decided to head at reduced speed towards Benina (airfield for Benghazi) that fortunately was close by, where we passed a few days waiting for a spare.
We were lucky to suffer no other damage, for only a few months before another squadron aircraft had a much more serious hail encounter over the Nile delta. In this case the actual hail was visible but still possible to see through, so that the pilot mistook it for rain - result being his windscreen was so severely damaged he had to switch to the right seat for landing (no trained co-pilot in those days, only an unqualified '2nd dicky'). Additionally the centre tail fin was completely carried away, and all four engines had their radiators so badly bashed in that they started to overheat – indeed their temperature readings were off the clock by the time they got back to Fayid.