I was sick yesterday and bored at home, so I took some time to research your question.
Unfortunately, it is still unclear to me whether a snow day will impact the time period for filing a response to an OA. The relevant rule, 37 C.F.R. 1.7, specifies that the "[w]hen the day, or the last day fixed by statute or by or under this part for taking any action or paying any fee in the United States Patent and Trademark Office falls on Saturday, Sunday, or on a Federal holiday within the District of Columbia, the action may be taken, or the fee paid, on the next succeeding business day which is not a Saturday, Sunday, or a Federal holiday." The question, therefore, is whether a snow day will qualify as a "Federal Holiday."
After expending considerable effort, I have been unable to locate any precedent indicating that a snow day will necessarily qualify as a Federal Holiday under rule 1.7. There have been a few instances where the PTO has indicated that certain circumstances will be considered a Federal Holiday, but those determinations were predicated on some major disaster (e.g., 9/11) or on an interruption of the operation of the U.S. postal service. In the latter case, the PTO often restricted the Federal Holiday designation geographically, i.e., to the regions of the country where postal service was interrupted. I did see one indication on a foreign law firm website that the USPTO considers accumaulation of snow "predictable" and therefore no extensions would be granted. I was unable to confirm (or disaffirm) that indication through independent research.