On the intermountain plateaus the winds do not blow very strongly, but in the Sistan Basin there are severe blizzards that occur during the winter, generally December through February. In the western and southern regions a northerly wind, known as the "wind of 120 days," blows during the summer months of June to September. This wind is usually accompanied by intense heat, drought, and sand storms, bringing much hardship to the inhabitants of the desert and steppe lands. Dust and whirlwinds frequently occur during the summer months on the flats in the southern part of the country. Rising at midday or in the early afternoon, these "dust winds" advance at velocities ranging between 97 and 177 kilometers per hour, raising high clouds of dust.
Temperature and precipitation are controlled by the exchange of air masses. The highest temperatures and the lowest precipitation prevail in the drought-ridden, poorly watered southern plateau region, which extends over the boundaries with Iran and Pakistan.
The Central Mountains, with higher peaks ascending toward the Pamir Knot, represent another distinct climatic region. From the Koh-e Baba Range to the Pamir Knot, January temperatures may drop to -15 C or lower in the highest mountain areas; July temperatures vary between 0 and 26 C depending on altitude. In the mountains the annual mean precipitation, much of which is snowfall, increases eastward and is highest in the Koh-e Baba Range, the western part of the Pamir Knot, and the Eastern Hindukush. Precipitation in these regions and the eastern monsoon area is about forty centimeters per year. The eastern monsoon area encompasses patches in the eastern border area with Pakistan, in irregular areas in eastern Afghanistan from north of Asmar to just north of Darkh-e Yahya, and occasionally as far west as the Kabul Valley. The Wakhan Corridor, however, which has temperatures ranging from 9 C in the summer to below -21 C in the winter, receives fewer than ten centimeters of rainfall annually. Permanent snow covers the highest mountain peaks. In the mountainous region adjacent to northern Pakistan, the snow is often more than two meters deep during the winter months. Valleys often become snow traps as the high winds sweep much of the snow from mountain peaks and ridges.
Precipitation generally fluctuates greatly during the course of the year in all parts of the country. Surprise rainstorms often transform the episodically flowing rivers and streams from puddles to torrents; unwary invading armies have been trapped in such flooding more than once in Afghanistan's history. Nomadic and seminomadic Afghans have also succumbed to the sudden flooding of their camps.
The climate of the Turkistan Plains, which extend northward from the Northern Foothills, represents a transition between mountain and steppe climates. Aridity increases and temperatures rise with descending altitudes, becoming the highest along the lower Amu Darya and in the western parts of the plains.