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Why do north-facing slopes in the Atlas Mountains receive more rain than south-facing slopes?

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Map showing the Atlas Mountains across Morocco, Algeria, and Tunisia in North Africa, with color shading to indicate elevation changes. Major mountain ranges, cities, rivers, and physical features such as the High Atlas, Anti-Atlas, Saharan Atlas, and surrounding deserts are labeled. An inset locator map highlights the region's position in northern Africa. — Atlas Mountains The Atlas Mountains.

The Atlas Mountains serve as a meeting point for two distinct air masses: humid, cold polar air arriving from the north and hot, dry tropical air moving up from the south.1

The difference in rainfall between slopes is primarily due to the influence of aspect, or exposure. North-facing slopes receive more precipitation because they are positioned to intercept the humid, moisture-laden air masses coming from the north. Conversely, the south-facing slopes are more heavily influenced by the hot, dry air masses originating from the Sahara to the south.12

This phenomenon is a form of orographic precipitation, where moist air is forced to rise over a mountain range, cooling and condensing to release rain or snow on the windward side. Because the Atlas Mountains act as a barrier between the Mediterranean basin and the desert, the northern slopes benefit from the moisture of the northern air masses, while the southern slopes often exist in a drier environment.32