Vanilla 1.13.2: unsure how to test.
Spigot 1.13.2: issue not present.
Vanilla 1.14: unsure how to test.
Spigot 1.14: issue present.
CraftBukkit 1.13.2: issue not present.
CraftBukkit 1.14: issue present.

Issue:
Spigot and CraftBukkit both fire WeatherChangeEvents roughly 20 times a second.

reproduction steps:
Run a 1.14 Spigot/CraftBukkit server.

All bugs should include the amount of time you spent on steps 1-8.
     I've spent about 20min writing up this report.