ᴡʜᴀᴛ ɪs ɪᴛ: ʟᴀʀɢᴇ sᴛʀᴜᴄᴛᴜʀᴇs ɪɴ ᴛʜᴇ ᴄʟᴏᴜᴅs ᴀᴛ 𝟷𝟶,𝟶𝟶𝟶 ғᴇᴇᴛ ʜɪɢʜ?

Airplane passenger states: was on a flight heading towards ft Lauderdale near Louisiana and when flying over the Gulf I saw something interesting after one and half hours into flight at an altitude of about 39,000 ft.
The pilot told me that the clouds below us in the plane are 6-10 thousand high up.