Upslope fog hugging the mountain surface occurs when:. 1. air cools because of decreasing atmospheric pressure; eventually air cools to the dew-point temperature 2. air warms because of decreasing atmospheric pressure; eventually air cools to the dew-point temperature 3. air warms because of decreasing atmospheric pressure; eventually air warms to the dew-point temperature 4. air cools because of increasing atmospheric pressure; eventually air cools to the dew-point temperature