If temperatures overnight are already very close to the freezing point, then this drop of just a few degrees can take the temperature below freezing.

如果夜间的温度已经非常接近冰点，那么仅仅下降几度就可以使温度降到冰点以下。

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When fog forms below 0C, its super-cooled water droplets remain liquid, even though the temperature is below freezing.

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These systems are not only important in the winter months, but also in the summer months, because at higher altitudes, the temperature is well below freezing year-round.

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"In wintertime, the cliff surface gets so cold that its temperature falls below the freezing point of CO2, which at low pressure goes directly to solid, " said Dr Musselwhite.

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