A medium-size (3.0-4.5 cm. wingspan) pale grey moth, slightly reddish or pinkish grey on the lower half of the forewing. The hindwing is whitish with some darkening along the outer veins and at the anal angle. The leading half of the forewing is light grey, with a large diffuse dark grey blotch at the disk, usually containing a small black discal dot. The pale grey area along the costa near the apex is not well defined as it is in Schizura leptinoides and extends further along the costa toward the base. The most prominent markings are the dark scaling on the forewing base which also extends part way along the inner margin (lacking in leptinoides) and the prominent dark grey blotch at the disc. Normal lines are absent or nearly so. Antennae are pectinate to beyond the midpoint, then simple. Both sexes are similar. The genitalia and the 8th sternite differ greatly from those of Schizura leptinoides. Western populations of semirufescens are paler and greyer than those from eastern Canada, and superficially resemble the southern O. perangulata. In Alberta, semirufescens is likely to be confused only with Schizura leptinoides.