
Regular verb: snow - snowed - snowed
Simple form | V-ing form | 
| - - it'd snow - - -  | - - it'd be snowing - - -  | 
Perfect | V-ing perfect | 
| - - it should've snowed - - -  | - - it should've been snowing - - -  | 
Simple form | V-ing form | 
| - - it shouldn't snow - - -  | - - it shouldn't be snowing - - -  | 
Perfect | V-ing perfect | 
| - - it shouldn't have snowed - - -  | - - it shouldn't have been snowing - - -  | 
Simple form | V-ing form | 
| - - should it snow? - - -  | - - should it be snowing? - - -  | 
Perfect | V-ing perfect | 
| - - should it have snowed? - - -  | - - should it have been snowing? - - -  | 
Simple form | V-ing form | 
| - - shouldn't it snow? - - -  | - - shouldn't it be snowing? - - -  | 
Perfect | V-ing perfect | 
| - - shouldn't it have snowed? - - -  | - - shouldn't it have been snowing? - - -  |