When the fog, the snow or the rain has visibilities down, you’ll hear conditions being described as “socked in”. General the term is used to describe weather at the airport when visibility or ceiling conditions are so poor that the airport is closed. The term actually goes back to early aviation days. At the time, wind direction and speed was indicated by a “wind sock”, a tapered cone of fabric. The direction the “sock” pointed and the amount it filled were important in landing calculations. You can still see wind socks at private fields across the country. But, if low ceilings or poor visibility, makes it difficult to see the “sock” the airport is considered to be “socked in”.
Mary Knapp, Weather Data Library