what means "low ceilling means in "The old man at the bridge"?

Question

The line comes from The Old Man At The Bridge By Ernest Hemingway.Here is the line:

It was Easter Sunday and the Fascists were advancing toward the Ebro.It was a gray overcast day with a low ceiling so their planes were not up

Answer 1

Ceiling refers to “altitude of the base of a cloud layer” according to the OED.

Ceiling /ˈsiːlɪŋ /
▸ noun

1. the upper interior surface of a room or other similar compartment: the books were stacked from floor to ceiling.
   • an upper limit set on prices, wages, or expenditure: the government imposed a wage ceiling of 3 per cent.
   • the maximum altitude that a particular aircraft can reach: the aircraft's quoted ceiling of 24,000 feet.
   • the altitude of the base of a cloud layer.

Origin

Middle English (denoting the action of lining the interior of a room with plaster or panelling): from ceil + -ing¹. ceiling (SENSE 1) dates from the mid 16th century.