A relatively large Abagrotis (3.8-4.3 cm wingspan). The forewings of males are dark red-brown, while those of females are usually lighter orange-brown. The markings consist of faint, doubled antemedian and postmedian lines, and a small oval orbicular and an elongate vertical reniform, both finely outlined in pale yellow-brown scales and at least partially filled with grey scales. The terminal area is usually paler and sharply defined from the remainder of the wing. The hindwings are dull brown-black with orange-brown fringe. The large size, dark red or orange-brown color and relatively complete pattern will separate alternata from the other Alberta species of Abagrotis. See also Abagrotis placida and cupida.