The best adjective in your context would be "overcast." As defined by Wiki:

Overcast or overcast weather, as defined by the World Meteorological Organization, is the meteorological condition of clouds obscuring all of the sky.

An example of overcast weather:

^{From Wikipedia}

"Cloudy" is fine, too. But if you want to convey that there is no sunlight at all, then this would not be the best option. You need to further describe it. Sky can be very cloudy, but this doesn't mean that there is no light striking the land because of the clouds, as clouds can very well be transparent.

You can, for example, see here:

You can read this definitions taken from ldoceonline:

The best adjective in your context would be "overcast." As defined by Wiki:

Overcast or overcast weather, as defined by the World Meteorological Organization, is the meteorological condition of clouds obscuring all of the sky.

An example of overcast weather:

^{From Wikipedia}

"Cloudy" is fine, too. But if you want to convey that there is no sunlight at all, then this would not be the best option. You need to further describe it. Sky can be very cloudy, but this doesn't mean that there is no light striking the land because of the clouds, as clouds can very well be transparent.

You can, for example, see here:

You can read these definitions taken from ldoceonline: