I would agree that it is most likely an immature red-tail. Here in Western Washington Red-shoulders are almost unheard-of, whereas red-tails are the most populous raptor in the state. Immature birds have a brownish tail until their second summer, and are often found preying (or trying to) on livestock because they are less-experienced at catching the more common prey of an adult (rodents, reptiles, small birds.) Especially with the bad weather it's likely that he was just having a hard time and wistfully longing for a hot meal. If he can't find any food at your place it's likely that he'll move on in short order. Scare tactics (flash tape, hung CDs, crazy people waving brooms, sudden loud noises) will help move them along faster sometimes. Odds are he won't be in the area long since young birds are highly mobile and don't have a well-defined territory yet.
