Summer Rainfall in Pakistan is primarily due to the monsoon. Pakistan lies at the tail end of the monsoon. The monsoon rainfall of Pakistan is highly unpredictable and much smaller in amounts than that of the monsoon of India.
The monsoon season sets in Pakistan as a result of moisture laden, winds entering from the Indian or the eastern side about the first week of July and continues up to the middle of September. The piedmont plains of the Punjab, the East Central Punjab, in which Lahore is located and the areas close to the Himalayan foot hills like Rawalpindi / Islamabad, Muzaffarabad etc. are the first among the stations to receive monsoon rainfall.
Since Pakistan is situated far away from the source of the monsoon, ie ,, the Bay of Bengal, when the monsoon enters Pakistan after traveling about 1000 miles over the Indian territory, it has already been robbed of much of its moisture. Therefore, the areas which get some rains are very few an comprises of Kashmir, Hazara, Rawalpindi, Gujranwala and Lahore divisions only. Even in these areas, only hill stations can be said to get appreciable rain. Plain stations in these areas get only moderate rain.
Apart from the districts mentioned above, there is little or no rain in other parts of Pakistan from the monsoon and the southern part of Pakistan is practically dry. As for the high mountain stations of the north are concerned, they also do not get any rain from monsoon because they are on the leeward side of the high mountains barriers which the monsoon winds cannot cross.
Having said this, the monsoon line in Pakistan starts from Lahore then curves northwestwards towards Islamabad Rawalpindi and thence to westwards up to Attack. Beyond Attock, there is practically no rainfall from the monsoon. It is interesting to note that Peshawar, which I only 90 miles west of Rawalpindi, gets less than one-fifth of the rain reported at latter station. Likewise Faisalabad that is almost the same distance westwards from Lahore gets less than half of the rain recorded at the latter station.
Monsoon rain beyond Muzaffarabad and Murree declines sharply and at the Northern Areas stations of Chitral, Gilgit and Skardu, it is practically unknown. Similarly Karachi, which lies on the coast gets less than one tenth of the rain fall of that recorded at Murree. Quetta, on the extreme west near the Iranian Border, has never recorded any monsoon rainfall and is totally out of the monsoon zone.
In short, monsoon in Pakistan covers a very small area which is no more than 10 percent of the total land area of the county and the monsoon rain is highly location sensitive.