First, the white snow reflects most of the Sun's energy. Notice that the only places where the snow is melted is around dark colored objects, such as the branches. Those objects absorbed more energy, converting much of it to heat.
Second, the ground under the snow is still frozen solid. That cold ground helps keep the snow cold enough to stay frozen.
Third, water and ice both have a high specific heat. Specific heat is the amount of energy that is required to raise the temperature of one gram of a substance by one degree. The higher the specific heat, the more energy it takes to raise its temperature. It takes more energy to raise the temperature of one gram of snow than it does to raise the temperature of the same amount of rock or wood.
Fourth, this is a north-facing slope, which means that it is mostly in shade this time of year. Less sunlight means less heating.
Thanks to those four things, our snow will probably be around for weeks.