The ground freezes 2-3 feet down in the winter.
When rain and warmer weather hit, the snow and top layer melts, but down deep it's still frozen. That means there's no place for the water to go.
So it makes a sort of soup up top.
90% of the snow has already melted in the last week, though. It's been raining all day, but it's a light rain.
FYI, stay alert Sweetie