Actually it's pretty much already here. It's cold out!
Here are a few things to remember that will help keep your pets safe during cold weather:
In spite of the fur coat, animals get cold just like we do. Pets with a thick fur and some extra padding (fat) will be relatively cold tolerant. But pets on the thin side and with short hair get cold very fast. Smaller animals (for example chihuahuas), young animals, and geriatric animals are also going to be more susceptible to the cold.
How do you know if your pet is cold? They want to come in right away, and they shiver. Just like people.
Even if they love the cold and never want to come in, that doesn't mean they aren't cold. Exposure to extreme temperatures can lead to hypothermia and frostbite in pets. So don't leave them out there too long even if they are having fun.
How can you keep your pets warm? Dry them off when they come inside (and before they go outside). Don't leave them outside unsupervised. If it's too cold for you to stand out there in a coat watching them, it's probably too cold for them to spend a lot of time outside. Consider a dog coat or sweater for short haired and smaller breed dogs.
Another frequent problem in the winter is sore feet. This happens for a variety of reasons. De-icing chemicals can be irritating. Snow and ice and can be sharp and scratch the feet. Feet that are wet are going to be more prone to injury and infection. Wipe your dog's feet when they come in from outdoors both to dry them and to remove salt and ice that might be stuck to the fur in between their toes. (It'll also help cut down on the dirty footprints in the house.) There are many booties on the market available for pets. If you are going to try that, make sure they fit well, as that will make it more likely the pet will let you put them on and keep them on.
Toxins are also a problem associated with winter. De-icing chemicals can be toxic. Try to buy those that are "pet friendly." Anti-freeze is toxic. Do not let your pets ingest spilled anti-freeze. If they do, consult your veterinarian immediately.
One last thing to be aware of: cats and other animals will sometimes crawl under the hood of a car in winter in an attempt to get warm. Starting a car with an animal under the hood can lead to injury or death to the animal and damage to engine. Bang on the hood a couple times to wake up any sleeping critters before you start your car. If you don't like winter, you can say a few naughty words when you do it. It might make you feel warmer.