How do variations in temperature affect the altimeter?
Pressure levels are raised on warm days and the indicated altitude is lower than true altitude.✓ Correct Answer
Higher temperatures expand the pressure levels and the indicated altitude is higher than true altitude.
Lower temperatures lower the pressure levels and the indicated altitude is lower than true altitude.
Explanation
Warm air expands, so on warm days a given pressure level lies higher than standard, and PHAK Chapter 8 explains that the altimeter then indicates lower than the true altitude. In cold air the pressure levels are lower and the altimeter indicates higher than true altitude, the dangerous case ('from high to low, look out below'), which is the opposite of the other two options.
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