The Indian Summer Monsoon and Mount Everest "Weather Window"
Compiled by AdventureWeather.com May 9, 2004
A monsoon is a seasonal shift in the prevailing wind direction, that usually brings with it a different kind of weather. The persistent wind flow is driven by a warm air mass with low pressure at the surface that forms over the continent as it is warmed by the sun. Air from the relatively higher pressure air mass over the ocean flows toward the low pressure over land. Probably the most famous monsoon is the Indian summer monsoon, as it affects such a large portion of Asia. In May and June of each year, the dry northerly wind flow over India changes direction, and warm humid air from the Indian Ocean flows from the south, gradually overspreading the Indian subcontinent. Widespread torrential rains, and even severe thunderstorms, accompany the "onset" of the monsoon. The Indian Ocean version of the hurricane, called a "cyclone", can also occur and move ashore in association with the onset of the monsoon. These cyclones have at times killed thousands of people who live in the low-lying areas along the eastern coast of India and Bangladesh. A weaker version of this monsoon occurs over the normally dry southwestern United States in the later summer when more humid air, accompanied by thunderstorms, invades the region. www.weatherquestions.com
The Monsoon blows from South-West, but moves mainly in a North-Westerly direction.
The monsoon strongly affect Indian financial growth. 2002 was the driest season in a decade. 2003 was the best in 5 years.
The onset of the monsoon off the coast of Sri Lanka mid-May, often accompanied by Cyclones high up in the Bay of Bengal, will signal the coming of the Everest famous Weather Window.
The Weather Window is a period with no Jetwind, low general winds and little precipitation perfect for climbing above 8000 meter. The majority of all successful Everest summit occur during the Weather Window that occur between app. May 15 and Jun 8, when the Monsoon hits the Himalayas (Jun 6 for the Kanchenjunga area). The climbing season as defined by government climbing permits ends June 1.
The length of the Weather Window is app. 2 weeks. The Weather Window might be disrupted by incoming weather systems.
Successful Everest spring season summits 5 year:
1998 May 18 May 27 May 20 25 climbers
1999 May 5 May 29 May 26 23 climbers
2000 May 15 May 28 May 16 23 climbers
2001 May 19 May 26 May 23 88 climbers
2002 May 16 May 30 May 16 77 climbers
Wind prediction charts:
Season Start date low wind period
2001 Spring Season May 19
2002 Spring Season May 23
Everest Autumn Weather Window:
By comparing charts AdventureWeather identified an autumn weather window. Check story http://www.mounteverest.net/story/stories/Ficklefallforecasts,AnautumnEverestweatherwindowSep172003.shtml
Monsoon Weather forecasting:
Special Weather Report May 13 2003
IMD - Indian
- Long Range Monsoon forecast presented yearly mid-April
- Daily and Weekly Weather reports
NCMRWF - National Centre for medium Range Weather Forecasting
- Monsoon View Charts
Onset and withdrawal of Monsoon