First, get a windowsill. When Mimi lived mostly outdoors I would see her trotting quickly down icy sidewalks or trying to plow her way through a snowdrift. I winced to think of her tiny paws on ice and rock salt and seeing her petite little self nearly be lost in the snow and many was the time I wanted to just go and get her and bring her inside. She was skittish and would run, but I was always glad to see that she had survived another day, another winter with all her extremities intact. Unfortunately, also, her uterus, but that's another story entirely, and likely one of the driving forces that kept her roaming, even in winter.
Now she takes advantage of every sunny windowsill and warm soft spot, and while she joins me on the deck when it's warmer, now that it's cold with ice and snow she stays inside and simply watches me go out to feed the birds, probably getting an extra measure of appreciation for where she is remembering the feeling of ice under her paws.
Don't take for granted that animals can survive outdoors. Simply because other animals live in the outdoors without human intervention doesn't mean that our pets can—and it doesn't always mean that those animals whose habitats are outdoors live well or even survive the winter. Wild animals also need and find adequate shelter and food and water if they don't hibernate, and if they don't find these things they don't survive.
Cats may tolerate cold for a while, but their small bodies lose heat quickly and extremities like tails and ears can easily be lost to frostbite. Small breed dogs like a Chihuahua with short, thin fur or a delicate Italian Greyhound with no body fat obviously don't have the resources of a squirrel who's doubled his fur and fattened up on nuts and fruits (and my bird seed and suet). Puppies and kittens are likewise less tolerant of cold than adults, likewise older pets. Cookie went outside with me every single day no matter the temperature and bravely walked on whatever had fallen from the sky, but as she grew older I would only let her wander for shorter times than she preferred, much to her consternation and protest. If pets go outside at all, they shouldn't be outside without protection for very long.
Aside from cold is also the risk of poisoning, either from leaking anti-freeze, always a risk but moreso when animals take refuge beneath a warm car on a cold day, and from products used to melt ice and snow. Fluids and oils from vehicles also tend to persist in snow and on wet pavement, so you should always wipe down your pet when they come inside, and wash off any sticky or oily substances on their fur. Remember that you also track these things indoors on your shoes, so be careful to place wet boots and shoes where your pets can't get to them, wipe them down as soon as possible (this is good for your boots and shoes anyway), and clean up the floor before someone licks up a puddle.
As for cute little coats they may be more than just cute and actually provide needed insulation for cats and dogs, but you can be the judge if your pet will wear one! Below are links to articles that will give you more detail on preparing your indoor-outdoor pets for the cold.
Cold Weather Tips from the ASPCA
Pet Winter Safety: Prepping Your Pet for Winter Weather from WebMD/Pets
14 Winter Safety Tips For Pets from Pawnation
Mimi is happy to say that this is as close as her children have come to experiencing snow—leaning out the window while feeding the birds!
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