Predicate 
snow:
  Frames file for 'snow' based on sentences in brown.
Roleset snow.01 Verbnet Class: NONE "weather phenomenon":
Roles:
Examples:
| classic weather construction (-) | 
|---|
person: third
tense: past
aspect: progressive
voice: active
form: participle
| He was mildly surprised to find it was snowing.
 
 | 
| REL: | snowing | 
The 'it' is just a dummy--it doesn't have any real meaning, so leave it out.
Comparison with 'rain' suggests the argument structure, but the corpus
doesn't provide examples.