Make a snow trench shelter Find a flat sheltered spot for your shelter. Don't go too close to trees or big rocks since blowing snow tends to accumulate around them.  Dig a hole in the snow, about a foot longer than your body and about 3 feet wide, use the snow from the dig to build walls around the hole. Try to get one of the short sides downwind. Keep digging until the hole is 3 ft from floor to upper edge. Keep in mind that the smaller your shelter is the warmer it will be. Leave a 1.5x1.5 ft opening in the downwind upper short edge with a connecting corridor as in the picture, this will be your door. If you plan to use a stove in the shelter you must also make a vent opening in the side opposite to the door. This opening should be about 6x6 inches. If possible, try to make a block of hard snow 1.5x1.5x0.5 ft to use as a door block, place this block inside the hole when you're done.       Cover half of the floor on the opposite side of the opening with soft branches to provide extra insulation from the cold snow beneath. This will be your sleeping area, you will later cover the branches with your sleeping pad. If you don't have a sleeping pad with you, make a thicker layer of branches. If it is snowing while you are building your shelter, you can do this step later, after the roof has been put up so you won't get snow on your branches. The sleeping area should be higher up than the floor since the air is a bit warmer higher up.       Place a number of tree branches over the hole as in the picture. Keep in mind that these branches may have to carry some heavy snow loads. You can use skis and ski poles for this purpose as well but keep in mind that you won't be able to use them again without ruining the shelter.        Cover the hole with your tarp. Attach edges and corners as well as possible with stakes made from tree branches or string to a nearby tree. Don't rely on weights such as rocks or big chunks of wood, they will start sliding. You want to make sure that there's no way that the tarp will start sagging or slip down through the openings in the ceiling. Cover the tarp with a layer of snow for insulation. If there is powder snow available try to get a coverage of at least 3 inches. If there is no powder use wet snow or hard snow to make blocks 1.5" thick to form a sheet on top of the tarp, try to rest the blocks on the support poles and not on the tarp. If it is snowing heavily you can let nature take care of this step.          Move in to the shelter. Put your sleeping pad on the branches and sleep with your head away from the door. You can block the door opening to keep warm but you must have at least two small air vents on opposite sides of the shelter to ensure an adequate air supply.    SOME THINGS TO KEEP IN MIND When you're using a stove in the shelter you must open both the door opening and the vent opening. Make sure that the vent opening is kept clear from falling snow on the outside, poke around with a stick periodically if needed. If you need to urinate during the night, don't go outside in the cold. Just go on the floor inside the shelter. The urine will seep down through the snow, there will be a stained crater left but you can just cover that with some snow.