Pakistan is a large country, about 1.5 times the size of France. Most of the country has a climate dominated by the Asiatic monsoon (see India climate). The climatic year may be divided into three principal seasons.
Mid-October to late February is the cool season with generally pleasant, sunny and quite warm weather by day, but also with chilly nights and occasional frosts. The northern and western parts of Pakistan receive some rain at this time brought by depressions moving in from the west. Conditions in the higher mountains at this time are distinctly cold. The hottest season is from early March until late June. During this period, midday temperatures in the south and centre of the country rise to very high levels, and the heat is distinctly unpleasant in spite of the low humidity. Some occasional rain, usually of a showery, thundery nature may occur at this time, and these brief thunderstorms are often preceded or accompanied by dust storms.
The rainy season over most of Pakistan is from late June to early October. This is the season of the south-west monsoon, and although temperatures are a little lower, the high humidity can cause discomfort.
Not all parts of Pakistan are equally wet during the rainy season. The desert region of the south and south-east receives little rain at this time and the area is hot and sunny. Jacobabad has the reputation of being one of the world's hottest places from April to September. Average daily maximum temperatures during that period range from 39 to 46 °C (102 to 114 °F). The extreme maximum temperature recorded is 53 °C (127 °F). Karachi, on the Arabian Sea coast, also gets very little rain and, although cooler than inland, has a very unpleasant climate at this time because of the higher humidity. The mountainous regions of the north and west receive much less rain during the south-west monsoon period and may be wetter during the cooler winter season. It is in the eastern and central plains that the full effect of the monsoon is felt. The climate here is similar to that of the northern plains of India (see India climate).
Sunshine amounts are high throughout the year in much of the country, ranging from six to seven hours a day in the cool season to 10 to 12 hours a day in the hot season. The cloudiness increases generally during the wet season even though some areas only have low rainfalls. For example, in July and August daily sunshine at Karachi averages only four to five hours even though the rainfall is much less than further north. Snowfall is heavy on the higher mountains in the north, and the melting snow together with the heavy monsoon rainfall feeds the five great rivers of the Punjab plains. Were it not for the irrigation flow from these rivers, much of the Punjab and Sind lowlands area would be a more extensive desert.
There is a danger of heat exhaustion or heatstroke during the hot season. The heat is often so great that, without air conditioning, indoor temperatures are extremely uncomfortable.