Pakistan has four seasons: a cool, dry winter from December through February; a hot, dry spring from March through May; the summer rainy season, or southwest monsoon period, from June through September; and the retreating monsoon period of October and November. The onset and duration of these seasons vary somewhat according to location.
The monsoon and the Western Disturbance are the two main factors which alter the weather over Pakistan; Continental air prevails for rest of the year. Following are the main factors that influence the weather over Pakistan. Western Disturbances mostly occur during the winter months and cause light to moderate showers in southern parts of the country while moderate to heavy showers with heavy snowfall in the northern parts of the country. These westerly waves are robbed of most of the moisture by the time they reach Pakistan.
Fog occurs during the winter season and remains for weeks in upper Sindh, central Khyber Pakhtunkhwa and Punjab.
Southwest Monsoon occurs in summer from the month of June till September in almost whole Pakistan excluding western Balochistan, FATA, Chitral and Gilgit–Baltistan. Monsoon rains bring much awaited relief from the scorching summer heat. These monsoon rains are quite heavy by nature and can cause significant flooding, even severe flooding if they interact with westerly waves in the upper parts of the country.
Tropical Storms usually form during the summer months from late April till June and then from late September till November. They affect the coastal localities of the country.
Dust storms occur during summer months with peak in May and June, They are locally known as Andhi. These dust storms are quite violent. Dust storms during the early summer indicate the arrival of the monsoons while dust storms in the autumn indicate the arrival of winter.
Heat waves occur during May and June, especially in southern Punjab, central Balochistan and Sindh. Thunderstorms most commonly occur in northern Punjab, Khyber Pakhtunkhwa and Azad Kashmir. Continental air prevails during the period when there is no precipitation in the country.