How to protect decking when it's already winter
The temperature range is important because it dictates the drying time and should be followed pretty close. The dryness factor is critical. Wood absorbs water. When you set out to protect your deck you want the deck to absorb the sealer. If the deck is already wet, then the sealer won't sink into the wood and you've wasted your money. The deck must be dry so it absorbs the maximum amount of sealer. This applies to water based sealers too.

If you feel the need to do something now, You can get a water proof tarp and cover your deck and then apply the sealers when the deck is dried out. Make sure to allow for air flow while the tarp is on the deck. Then keep the tarp on the deck until the sealer dries, still allowing for air flow. Otherwise, wait until spring. Good luck.