This may be a good year of all years to keep an eye out for this species in Maryland.  There have already been confirmed sightings in Colorado and along the South Dakota/Nebraska border.  Another unconfirmed sighting of TWO Ross's Gulls was just reported in the UP of Michigan.  Though this sighting might be of transient birds and might never by confirmed, the observation reports provided to eBird seemed accurate for Ross's Gull.  
 
This pattern may indicate some relatively widespread vagrancy of this species from Siberia this year, as this rate of frequency is unprecedented in recent years, particularly in the Lower 48.  It would be interesting to investigate what weather patterns or ecological phenomenon might be contributing to these sightings.  Perhaps the Siberian fires this past summer has affected their winter habitat in some way?
 
 
Ross Geredien
Annapolis/Edgewater