As monsoon starts to retreat from Northwest India in second fortnight of September, the weather starts changing for better. From uncomfortable warm sultry days of Monsoon, it becomes comfortable in the day with mornings & evenings becoming pleasantly cool, with slight nip in the air. This is mainly because Cool dry air starts ushering a season of azure blue skies, mild sun, good visibility & no rain over entire country except Tamil Nadu & Kerala, which experience retreating Monsoon or Northeast Monsoon.
This is the most awaited period by aviators, as weather conditions are just ideal, Hang-gliding, Para-sailing & Hot-air Ballooning. This period is known as Post-Monsoon period in meteorological parlance which is equivalent to Spring in USA & Fall in UK. It covers months of October & November.
According to Skymet Meteorology Division in India, the highlight is that the season has almost no aviation weather hazards mainly in Nortwest & Central India.
Mild Temperatures: Surface temperature is the single most important and decisive factor for the `all up weight` for the airplane to lift off but with temperatures ranging from a high 32 to 340C , aircrafts are able to carry more passengers/load than what are able to carry in summer monsoon.
Maximum temperatures drop below 30°C by late October and there is a gradual fall in average temperature. Minimum temperatures drop below 20°C. During Autumn, the wind direction begins changing from Southwesterly to Northwesterly.
Wind Shear: As airflow streamline steadies to moderate westerly flow, the threat of wind shear becomes negligible. However, Clear Air Turbulence (CAT) is a cause for concern over mountainous terrain as it can lead to uncontrolled swaying and bumpiness leading to anxiety among the air travellers. Aviators need to exercise extreme caution while flying in Hilly areas or in the vicinity of hills.
Humidity: With the advent of Dry cool air from the North, the humidity drop is dramatic. From about 70-80% in Monsoon, humidity comes down to 30%-40% by end of Oct, rendering days & nights pleasantly comfortable.
Weather Systems: This period is excellent for flying because there are no major weather systems affecting this period as WDs have yet to make their presence felt, Westerly Jet is not very strong to cause concern. Temperatures are not low & humidity is not high enough for mist/fog to form. The only jarring note is provided by formation of a cyclone in Bay of Bengal, Which can cause loss of lives & damage to property due to high winds, heavy rains, tidal waves & Storm surges. During the life-cycle (3-4 days) of a cyclone, the weather within 500 km radius of its centre is highly hazardous for any kind of flying & is best avoided.
Hence, Oct-Nov is the period when flying conditions are their best, & weather is ideal for outdoor activities like Golf, Cricket & picnics. So, enjoy till sun shines.!!
