Q. Will winter's cold temps affect my hybrid's gas mileage?
A. Cold temperatures will reduce the fuel economy of all vehicles, not just hybrids.
We can't tell you how much gas mileage you will lose during the winter because that depends on how cold it is, your driving style and traffic conditions. We can tell you that winter weather takes a toll on fuel economy and batteries, so with a hybrid you're being affected on two "cold fronts."
Cold weather means it takes longer for a car's engine to reach normal operating temperature, when it achieves its best fuel economy. Even once the engine is fully warm, though, you'll probably get lower gas mileage when the temperature is 8 degrees than when it's 80. Additionally, motorists in some areas report lower mileage during the cold months because oil companies use different blends of gasoline.
Likewise, batteries operate at a more optimum level when it's warm outside (but not Death Valley hot), and their effective capacity is reduced by frigid temperatures. With a hybrid, you may notice that the car doesn't operate in its electric-only mode as long as it does in milder weather. One reason is that the engine has to operate more often to generate the heat that warms the interior.