In Sweden we use two techniques for winter
In forest: digging straight down, then covering with pine branches.
The cut is as big as your sleeping mat. We call this ’snow grave’
The other one, a kind of snow cave, we call it snöka, excellent in the tree less mountains, is to find s snow drift, deeper than your ski pole,.
First you poke the skipole (upside down) in the middle of your planned dig.
If it has a vertical side you dig a small entrance hole, slightly smaller than your backpack, then a tunnel maybe 2.5 meters long. For one person you then do a ledge a foot or so above the floor on one side. Two people - one ledge on each side.
You close the entrance by pulling the backpack towards the opening from the outside.
The pole that sticks down you use to create an airhole.
The idea with the ledge is that the cold air sinks down and escapes through the entrance.
The snow grave is quick, and can be used (without any branches) in the mountains.
You then let snow cover yourself and the sleeping bag inside the grave.
You place /wedge the backpack over your head.
Cold but you will survive.
The cave takes longer to make, but the temperature inside gets up to maybe -1C, which is perfectly fine.
In a snowstorm you can not build an igloo.