This is the 10512th most frequent French word.
lourd
Heavy.
Here, 'lourd' is used to describe the physical weight of an object.
Ce sac est très lourd.
This bag is very heavy.
In this context, 'lourd' refers to social awkwardness or persistency that becomes bothersome.
Son comportement était lourd et agaçant.
His behavior was overly persistent and annoying.
In this usage, 'lourd' describes the oppressive or stifling quality of the atmosphere due to weather conditions.