I have forced Forsythias in NH just about every year for decades. I cut the branches in mid February, put them in a vase with water and watch them bloom. I do not soak them overnight; do not cover them with plastic nor do I put them in a cool place to let the buds swell. If the humidity in your house is so low that you need to go through that process to get a few Forsythia branches to bloom, you really need to invest in a good humidifier, if only for the health aspects.
I have forced Forsythias in NH just about every year for decades. I cut the branches in mid February, put them in a vase with water and watch them bloom. I do not soak them overnight; do not cover them with plastic nor do I put them in a cool place to let the buds swell. If the humidity in your house is so low that you need to go through that process to get a few Forsythia branches to bloom, you really need to invest in a good humidifier, if only for the health aspects.