As Nanda has correctly mentioned, in the 3D analysis, the force and pressure are related to each other. You can follow the link above to learn more about the basic application of force and pressure. In addition to that, the accuracy of the result and the application of force and pressure depend on the model. generally, the force will come into existence when two solid bodies are in contact, and its direction will vary along the X, Y, and Z components or in the desired direction, but the pressure will come into existence when the solid and liquid come into contact. The direction of pressure will always be normal to a solid surface.
As we can consider that the snow is uniformly distributed over the surface of the steel plate (with some slope), the weight of the snow will act vertically downward (we are considering some friction between the snow and the surface; otherwise, the snow would slide down). If you are considering a nonlinear analysis wherein the steel plate will deform, then the pressure load can change direction to adjust the direction normal to the surface, but the force will always act vertically downward. So again, the accuracy will depend upon the model, mesh size, and type of analysis (linear and non-linear) to be performed.
All the best