somberly

done or said with a heavy, sorrowful, or deeply serious mood, often with little brightness or humor — for example, speaking gravely at a funeral, walking quietly after bad news, or sitting still with a sad expression.

• gravely

  more focused on seriousness and importance than on sadness

• solemnly

  implies dignified, ceremonial seriousness rather than personal sadness

• mournfully

  stronger emphasis on grief and loss

• darkly

  can mean 'in a threatening or pessimistic way' — broader than 'somberly'

• cheerfully

  opposite in mood — light and happy instead of heavy and sad

• brightly

  opposite in visual quality — full of light and color instead of dark and plain