If the vehicle has been well maintained you just need a few small changes. The coolant that protected your engine from Florida heat will protect it from Washingtons' cold. If you will be driving in snow on a regular basis, you may want snow tires or all season tires, especially if this will be your first experience driving in snow. Make sure the windshield washer fluid you use contains a deicer, winter wiper blades may also be a good idea. Pick up a snowbrush and a windshield icescraper. Remember when clearing the snow off your vehicle to clear all of it off. If you leave snow on the roof, it will fly off at highway speeds,potentally causing an accident if it hits another vehicle.Some people suggest keeping the fuel tank at least 1/2 full,just in case you get stuck or the roads get bogged down during a storm.