The most common and most likely answer to this crossword clue is the 7 letter word SNOWCAP
I've seen this crossword clue in The Times
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More clues leading to the result SNOWCAP
Buddy explains!

The straight part
We know that "winter covering" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case winter covering = snowcap.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SNOWCAP mean?
SNOWCAP noun- A layer of snow covering a mountain top.
- A small hummingbird, Microchera albocoronata, which is a resident breeder in Honduras, Nicaragua, Costa Rica and western Panama.