They have a clause in their guarantee ( Terms and Conditions ),
about weather being one reason that voids their refund policy.

Reference Page 10 of their Terms and Conditions,
Under "C" - Exceptions, subsection # 2 = "see Liabilities Not Assumed"
Which can be found on Page 9,
and subsection "D" is where "WEATHER" is one of the MANY reasons they will not "assume liability" for "delay" or "damage" to packages.

FedEx Not Liable for Delay or Damages
0 Items