Beclouded
mean clouds
**Mean** as in petty or stingy—clouds that won't commit to real weather. Dickinson personifies nature as small-minded.
Debates if it will go
A single snowflake **debates**—Dickinson gives it consciousness and indecision. The weather can't make up its mind.
complains all day
The wind is **complaining** like a petulant person nursing a grudge. Nature reduced to whining.
Without her diadem
**Diadem** = crown. Nature caught undressed, lacking her usual majesty. The whole poem builds to this admission.