The climate of Pakistan is generally hot and dry throughout the year except a brief spell of rains during the monsoon season and a light rain in the very short winter season. The climate of the country as a whole can be divided into four seasons:
1. Winter: December to Mid-march
2. Pre-Monsoon: Mid March to June
3. Monsoon: July to Mid-September
4. Post Monsoon:Mid-September to November
Now I will discuss each season in detail.
1. Winter Season
Winter season sets in the early part of December. It is the most beautiful season on the plains of the country where days are mildly cold with temperatures in the range of 21C ( 70 F) through out the country. Nights however are a bit cold. On the hill stations however the max temperature is around 10 C ( 50 F ) and there is snowfall also. Winter season is generally dry, sunny and pleasant except for a little rain caused by western disturbance. Western disturbance is a rain bearing system having its origin in the Mediterranean sea. It travels all the way from there to Pakistan passing along its way through Israel, Jordan, Syria, Iraq, Iran, Afghanistan and finally it reaches Pakistan.
Since when it reaches Pakistan it has already traveled more than 3000 km and having shed most of its rain along the way, this is the reason that Pakistan gets little rain as compared to other counties mentioned above. The cities closer to the hills like the Capital Islamabad gets most of it while Lahore a major industrial city gets some rain also. Western Disturbance passes through Pakistan on the average once every 15 days from January to Mid March. The duration and intensity of winter season is directly dependent on the western disturbance. In those years when it is sufficient rain, the cold seasons prolongs and when the rain is meager, winter gets contracted and gives way to a long Hot summer.
2. Pre-Monsoon Season
By the middle of March it gets hot enough on the plains. The temperature being around 90 F ( 32.2 C). Since the winter rains gradually diminish and the air is very dry, the temperature rises sharply so much so that by the middle of April it is normally above 100 ( 38 C) and by the first week of May temperatures up to 110 F ( 43 C) must be expected. The suns shines as brightly as ever and a very hot and dry wind ( locally called Loo ) blows most of the time. Sometimes an isolated thunderstorm brings down the temperature to around 95F ( 35 C) and brings some comparative relief. All the vegetation is dried up.
The flora are under severe hygrothermal stress. Humans prefer to do any outdoor activity in very early morning for no sooner the sun rises than the temperatures climbs sharply. Generally the season is dry with a very scanty rainfall. Such high temperatures when sustained for months together create a great low pressure on the plains of Pakistan attracting the moisture-laden winds (Monsoon) from the Bay of Bengal and the Arabian Sea. Since this season is a preparation of Monsoon so it is called pre-monsoon season by the meteorologists. The state of affairs described above continues till the end of June when monsoon arrives with great vigor.
3. Monsoon Season
The word monsoon comes fro the Arabic word mausim meaning weather. These are moisture-laden winds bearing low, dark clouds full of rain. In normal years monsoon reaches Pakistan by the first week of July and remains active up to mid-September though the main months are July and August. Monsoon arrival lowers the temperature considerably.To give you an example when the monsoon strikes Lahore, the capital of province of Punjab, the temperature falls from a little above 100 F (38 C) to about 80F ( 27 C) within 24 hours.
Monsoon however is a mixed blessing. On one hand the temperature considerably reduces but on the other hand humidity rises to unbearably high levels. Before monsoon the relative humidity is in the range of 20 -30 percent in the afternoon, It rises sharply to 70-80 percent upon arrival of monsoons. The result is an increase in Heat Index and people feel very uncomfortable when sun suddenly comes out from behind the clouds at midday after a heavy downpour.
So the general pattern of monsoon is like this: when it rains the weather is cool and pleasant, otherwise hot and sultry. Sometimes heavy rain falls two to three days in succession and on other occasions almost whole of the month passes without any sign of rain. These conditions continue with more or less intensity till the middle of September when monsoon rain ceases and weather again becomes dry but this time it is not so hot.
4. Post Monsoon Season
As the name shows it follows the monsoon season. It includes the months of October, November and half of September. The season is very dry indeed. In fact it the driest of the four seasons. Since no monsoon passes through the country during this period and also there is no sign of a western disturbance like in winter so the precipitation is very low. Sometimes whole season passes without a trace of rain. Since the atmosphere is dry and skies clear the days are generally warm the temperature being around 100 F ( 38 C) in September but after the middle of the month a slight fall in night temperature is noticed.
This season in Pakistan is well known for its marked difference between the high and low temperatures, its dryness and its monotony. Sometimes the day and night temperatures differ by more than 15 degrees C ( 27 F). Such a huge fall of temperature at night make them pleasant while the days continue to be warm till the start of November when the day temperatures show a gradual fall. The season is ideal for any outdoor activity or function since chances of any rain or thunderstorm are rare and the heat also is not so intense as that of the pre-monsoon season. Sometimes when on rare occasions a heavy rain falls, it accelerates the advance of the winter season which normally starts by the beginning of December.
This is in short a brief sketch of the climate of Pakistan which is neither exhaustive nor complete but it does gives one an idea of what type of weather one should expect in Pakistan when on a business tour or a vacation.