While the literal hail falls in the stone-giants’ game in chapter 4 and a metaphorical hail of arrows comes ten chapters later, most uses of “hail” are not about weather but the homophone meaning to call out in address.  The original call was an interjection wishing the addressed person good health.  Waes hael! 

• 04.005 and the hail about
• 10.009 and voices hailed the raft-steerers.
• 11.031 and hailed the dwarves,
• 13.041 Then he hailed the others,
• 14.013 A hail of dark arrows leaped up
• 15.032 Thorin hailed them:
• 15.045 Again Thorin hailed them
• 15.046 Hail Thorin!
• 17.001 and hailed them,
• 17.004 Hail Thorin!’
• 18.015 Hail! Thorin,’

Harper, Douglas. “Hail”. Online Etymology Dictionary. Web.