Intermediate-level cover at last sent out with tours (11)
I believe the answer is:
altostratus
'intermediate-level cover at last sent out with tours' is the definition.
I can't judge whether this defines the answer.
'level cover at last sent out with tours' is the wordplay.
'level' becomes 'als' (I can't justify this - if you can you should give a lot more credence to this answer).
'cover' is an insertion indicator.
'last' says to take the final letters.
'out with' indicates anagramming the letters (out can mean wrong or inaccurate).
The final letter of 'sent' is 't'.
'at'+'t'='att'
'att' anagrammed with 'tours' makes 'tostratu'.
'als' placed around 'tostratu' is 'ALTOSTRATUS'.
Can you help me to learn more?
(Other definitions for altostratus that I've seen before include "Sky feature" , "Cloud forming a uniform layer" .)