snow clouds; snow-laden clouds
Refers to clouds that look like they will bring snow, or clouds from which snow is falling. Common in weather descriptions and literary contexts.
空には重たそうな雪雲が広がっていた。
Heavy-looking snow clouds spread across the sky.
雪雲が近づいて、急に寒くなった。
Snow clouds approached and it suddenly got cold.
Compound of 雪 (ゆき, snow) and 雲 (くも, cloud), with rendaku voicing of くも to ぐも.