Of or relating to winter; wintry. A synonym for 'hibernal' (think 'hibernate').
Etymology: mid 1500s, from Latin hiems, winter.
brumal (bro͞o′məl), adj.
Of, relating to, or occurring in winter.
Etymology: early 1500s, from Latin bruma, winter.
So, how do these words differ? I'm not entirely sure....
I see online comments about hiemal meaning 'pertaining to winter' while brumal means 'belonging to winter'...which I suppose could be the distinction between "wintry" and "occurring in winter" in the above definitions.
Looking to the Latin...'hiems' might be related to snow; 'brume' might have originally meant something like "season of the shortest day" (winter solstice).
So I guess if I had to try to use them distinctively in a sentence, I'd say something like "I attribute the hiemal weather to the brumal time of year".
The weather here isn't hiemal yet...the picture below is from a couple years ago. (Despite the red head, that's a red-bellied woodpecker.)