According to the Canadian Wildlife service web site http://www.cws-scf.ec.gc.ca/hww-fap/hww-fap.cfm?ID_species=45&lang=e this is what is stated about the sex of the Snowy:
 
The heaviest of North American owls, the Snowy Owl stands almost half a metre tall, with a wingspan of almost 1.5 m. The female is larger and heavier than the male (average weight of 2.3 kg versus 1.8 kg), as is the case with most diurnal birds of prey and owls. This is the reverse of the situation in most other families of birds, where males are typically larger than females, and has been the subject of much speculation.

Adult males may be almost pure white in colour. Adult females are darker, their white feathers barred with dark brown. First-year birds of both sexes are more darkly marked than their adult counterparts. Immature males resemble adult females, whereas immature females are heavily barred and may appear dark grey when seen from a distance.
 
(Their sources seem to be well documented--such as the Canadian Journal of Zoology and National Museums of Canada.)
 
Owling.com has this to say:

Description: The Snowy Owl is a large owl with poorly developed ear tufts that are usually not visible. The male can be entirely immaculate white although usually shows some spots or bars of dark slatey brown or black  on the crown, back, wings, and/or tail. His under parts are also generally marked with narrow bars on the abdomen, flanks, and sides. The adult female is much more heavily barred and noticeably larger. Only her face, center part of breast, and back of neck are unmarked white. The barring also tends to be more blackish. Both male and female have small, in comparison with other owls, brilliant yellow iris. The Snowy Owl is primarily diurnal (active in daytime). It is the most massive (greatest average weight) of the North American Owls and believed, by many, to be the most powerful. It has feathered feet and its large sharp talons and dull black bill are almost buried in its fluffy white feathers. It is also almost totally silent outside of its breeding grounds.

 
Here is another good website with great pictures: http://www.owlpages.com/species/nyctea/scandiaca/Default.htm
 
 
As white as this bird is--my instinct is to say it is an adult male.
 

Debra Fortenberry Priest
22 Hamlin Hts. Dr.
Hannibal, MO 63401
Tel: 573-221-3139
Cell: 573-248-9555
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