The onset of a wet, dark Northwest winter leads me to something I rarely do: offer my latest best thing, which this time is the microwaveable SnuggleSafe heatpad. This is currently helping keep our black porch kitty warm while she thinks about moving into the house.
I agonized over buying this, because it's about $27 plus shipping, but it's taken a huge load off my mind. The SnuggleSafe is a thick pink plastic disk that you pop in the microwave for however many minutes depending on the voltage of your appliance - the packaging will tell you exactly. It comes with a fleece cover so you don't have to buy that extra.
Does it provide little porch kitties 12 solid toasty hours? Well, no, because it is cold outside and a lot of heat just poofs off into the chilly, chilly ether. But I can tell you for sure it is still warm after 5 hours in the wooden box we made for her. So if you have some critters that can stand some safe and dependable heat, try this.
Here's the link to get one through my affiliation with EntirelyPets.com.