Introduction:
In the northern hemisphere, the direction a slope faces can greatly impact its temperature. The warmest slope in the northern hemisphere is the south-facing slope.

Explanation:
There are several factors that contribute to the south-facing slope being the warmest in the northern hemisphere.

Sun Exposure:
- South-facing slopes receive the most direct sunlight throughout the day. As the sun rises in the east and sets in the west, the south-facing slope is exposed to sunlight for the longest duration.
- The sun's rays are most intense when they strike the surface at a perpendicular angle. Due to the tilt of the Earth's axis, the south-facing slope receives the most direct and intense sunlight, resulting in higher temperatures.

Heat Absorption and Radiation:
- South-facing slopes have a higher capacity to absorb and retain heat compared to other slopes.
- When sunlight strikes the surface of the slope, it is absorbed, and the energy is converted into heat. South-facing slopes have a greater surface area exposed to sunlight, allowing for more heat absorption.
- The absorbed heat is then radiated back into the atmosphere, warming the air above the slope and contributing to higher temperatures.

Microclimates:
- Due to the exposure to sunlight and heat absorption, south-facing slopes often develop microclimates that are conducive to warmer temperatures.
- The warm air on the south-facing slope tends to rise and create a thermal uplift, which can trap heat and create a relatively warmer environment.
- The microclimate on a south-facing slope may also be sheltered from prevailing winds, further contributing to the warmer temperatures.

Conclusion:
In summary, the south-facing slope is the warmest compared to other slopes in the northern hemisphere due to its exposure to direct sunlight, increased heat absorption, radiation, and the development of microclimates. These factors combined make the south-facing slope the ideal choice for those seeking warmer temperatures.