Well, There is a book that was restored recently called "Red Army's Do-it-Yourself, Nazi-Bashing Guerrilla Warfare Manual" which was recreated from the Soviets 1940's fighting manual, one of the many tactics included was how to entrench, and one of the many listed ways was to entrench using snow, by putting aprox. 3-4 meters of heavily packed snow in front of your trench or 4-5 meters of light pack snow in front of your trench to effectively stop bullet fire from the enemy.

Here is a picture of one of the snow trenches

You can see that they have a fair amount of snow quickly compacted in front of the trench for quick protection, this is the sort of thing you would probably see. Plus, since you were already digging snow to make your trench, it was in readily available quantities for use.

EDIT: Adding my source, found the book finally. APA Citation: Grau, L., & Greses, M. (2011). Revolver and Pistol. The Red Army's do-it-yourself Nazi-bashing guerrilla warfare manual the partisan's companion (Updated and rev. ed., p. 113). Philadelphia: Casemate Publishers.