Is it okay to leave my MacBook in a cold car?

I don't think anyone can say with any certainty. Your refrigerator is on the order of 40 deg F and your freezer is maybe 10 deg F. How comfortable are you with putting your MacBook in either environment for a day?

I think the problem would be with condensation forming when the cold computer is brought inside. It might be safer if you can find a ziploc bag large enough to hold it, and not remove it from the bag until after it is back up to room temp. The condensation would be kept outside the bag.

There is no problem with doing that ...the problem occurs when you use your Macbook when it has not been allowed to warm up to room temperature (allowing time for condensation to subside as well). I've had my book locked in my car overnight at -20cel. - simply let it warm up before you turn it on.

Operating Environment
Operating temperature: 50° F to 95° F (10° C to 35° C)
Altitude: 3048 m (10,000 ft.) maximum
Relative humidity: 0% to 90% non condensing.

I'll not do it.

Mid-20s Fahrenheit is sub-zero in Celsius, which we use where I live...nevertheless, I would be careful and concerned about condensation, capacitors, and other circuits if operated when the computer is below freezing cold. The operating temperature for the MacBook is 50°F to 95°F (10°C to 35°C), and the storage temperature is -13°F to 113°F (-24°C to 45°C), according to Apple specs,so you should be okay.

:))

Well, yes and no...the answer involves what will typically happen (nothing) and what can happen. Some parts of the inner workings of your computer are designed to function within a set range of temperatures---exceed those temps, as in leaving your computer in subzero temps all day, and things may not work right, if at all, until it warms up. What I would be most concerned about is the condensation that will occur when rapidly warming the computer, so in that case, don't...let the computer reach room temperature before turning it on.

The short answer is that it is probably ok to leave it in the car in sub-zero temps all day---if you let it warm up before turning it on. I do it all the time, and my computers are fine. That being said, I don't turn them on when they are frozen to "check" them---I let them sit at room temperature for an hour or so before turning them on.

I also suspect that if any damage occurred as a result of trying to operate your MacBook outside the recommended operating temps, then that damage would probably not be covered under the warranty.

Find a bag or wrap it up in blankets that will also insulate your Macbook from the cold. I'm no expert, but I'm sure there are.

Maybe check http://www.rei.com

From the Tech Specs page for the MacBook:

Operating temperature: 50° to 95° F (10° to 35° C)
Storage temperature: -13° to 113° F (-24° to 45° C)

Like the other posters have said, condensation could be a problem. You'll probably be taking it from cold outdoors to fairly dry air indoors, so I wouldn't worry too much. Just let it warm up before using it.

Others have answered true to this question: Whenever you're laptop is stored in other than normal (50-90F) temps, ALWAYS temperature acclimate it to room temp prior to starting it up, whether cold or hot. They're always meant to run at the temps that humans are used to.