Can a landlord say that you cannot move out during the winter months?
The season has nothing to do with it. If you move out in the midle of your lease, the landlord could sue you for the remaining months of rent due under the lease. And the landlord does not have to help you move out if they don't want e.g. does not have to make a freight elevator available to you, or have their staff stay late or come in early or on a weekend to accomodate a move. And finally, if you do move out in the winter and somehow damage the property in doing so e.g. let pipes freeze somehow, they could sue you for the damage and/or take it out of your security deposit. But they can't refuse to let you move out in the winter unless you signed a written lease stating that you can't move in winter--if you did, that lease provision is enforceable as a contract.