The skies in the hills tops is usually very clear and because of this very clear atmosphere, the mountain tops cool very quickly as the warmth is radiated back to the air at a really large rate. The end result is that the mountain slopes become considerably cooler than the surrounding atmosphere. As it warms, it will become thick and dense because density is inversely proportional to the temperature. Now if it was a plain area, this trendy dense wind would have sinked into the lower level, close to the floor, until morning but as in our case it’s a mountain slope, so under the action of force of gravity it slips down the mountain slopes towards the deep valley below and compels the temperature there to become rather cool. The speed of the end is dependent on the gradient of the slope and the temperature in the source area. As it falls from the mountain top towards the valley it’s also referred to as fall wind. Another name for this end is katabatic wind.
Clear skies devoid of any clouds, little or no wind in the mountain top and low relative humidity are the prime prerequisites for the mountain or fall breeze to set in. Clouds and rains etc. disturb this happening severely.
The effect and situation of Gilgit
The channel of Gilgit is a low valley located at about 4500 ft. above mean sea level in the northern regions of Pakistan. It’s surrounded by very high mountains with peaks 15000 ft or more. The region is usually dry with very little rain. This makes this channel an perfect case for the mountain breeze to exert its effect.
In late July to early August, it so happens that Gilgit becomes hot during the day-being from world of monsoon, the atmosphere is dry so gets warmed up quickly and by mid-afternoon, the temperatures can reach as large as 110 F. The surrounding mountains shirts, nevertheless, stay 40- 50 F cooler during the day. During night, as a result of clear atmosphere on the hills, the temperatures start falling rapidly and reach around 50 F. As explained above, the atmosphere along the slopes becomes really cool and begins sliding towards the Gilgit valley and is most effective before sunrise when they could make the minimum temperature of Gilgit as low as 60 F. This is all because of katabatic wind. This occurs normally from late July to mid-August. If we celebrate the climate of Gilgit closely, the second western disturbance occurs in this region with its oceans, rain and strong winds, the High of Gilgit becomes 95 F and low rises to 75 F that is a clear sign that the mountain end effect is disrupted.