Himalayan mountaineering - pre-monsoon vs post-monsoon

Question

The four seasons in the Indian subcontinent are Winter, Summer, Monsoon, Autumn. The monsoons go on for a few weeks on end, and bring heavy clouds and rains/thunderstorms, and often enough, floods.

A few parts of the Indian-Nepalese Himalayas (e.g. some of the Kashmir ranges) do not receive the monsoon.

But in general, the Himalayas are thoroughly exposed to the monsoon, (some sub-ranges more than others), and no climbing is possible during this season.

Further, winter mountaineering is not a common thing there; there are very few winter expeditions, typically only by highly experienced folks.

So this leaves the average climber with two options - pre-monsoon and post-monsoon seasons for mountaineering.

I want to understand what differences (e.g. weather patterns, snow/ice conditions, etc.) should be expected between the pre-monsoon and the post-monsoon seasons.

Answer 1

Keeping the scope limited to India:

It is worthy of noting that the climate in western Himalayan region is pretty much defined and heavily influenced by what happens in southwest during it's monsoon season (from June to September) and by that in western systems (from November to March).

The names marked with an asterisk (*) are states in India I'll be referring to. If you observe, there are 6 states in India that have Himalayan ranges.

State of Kashmir is not heavily influenced by south-western flows. This region sees a mild rainfall during monsoon season, but experiences a heavier snowfall in winters. Pre-monsoon (April to early-June) are pleasant. You are not expected to have substantial snow-level up to an altitude of 5000m. Snow from the previous winters may be already in the melting cycle, causing streams to have higher water levels and force during the peak hours of day - 11:30 am to 2:30 pm. Beyond 5000m expect patches/sections of snow on almost all north faces of mountains. The higher you go, snow levels are more prominent. Post monsoon - all the moraines will be pain to cross, but rejuvenated grasslands will be a treat to the eyes.

Ladakh (Union territory of Ladakh) has an extreme weather. There is no monsoon season as such here. It receives very minimal rainfall. This is because it falls under a rain-shadow region being surrounded by high ranges from southern parts (sub-sections) of Himalayas and Karakorams in the north. Expect dry weather throughout the day with temperature reaching up to 32-35 Celsius, high winds around evening and very cold nights. Most of the region is cold desert so it poses a different challenges in mountaineering. This region has a lot of technical peaks above 6000m and high altitude passes. Most altitude gain would be dry moraines and expect a lot of mixed climbing above 5500m. Pre-monsoon and post-monsoon is not a valid discussion for Ladakh.

The state of Himachal Pradesh and Uttarakhand are considered paradise for mountaineers in India. I have observed that the average rainfall during the monsoon is slightly higher in state of Uttarakhand than Himachal Pradesh. Monsoon season is considered to be around months of June to September. These states see a heavy snow falls by the end of month of November and high-altitude peaks are difficult/impossible until the snow melts, which is in late March. It is noteworthy to know that most roads and high-altitude passes are opened during the month of April. That makes reaching certain camps easier. In a nutshell, you can start expeditions in pre-monsoon, around month of April/May and expect better conditions for mountaineering. A lot of streams with fresh cold water melting from some or the other glacier. Expect patches of snow above 4000m. The northern faces of these sub-ranges are much much colder and receives a lot of snow.

I can't answer for state of Sikkim or other ranges in the north-east states of India.

In my opinion, weather in Southern sections of Tibet will be much like Ladakh.

Answer 2

So after spending about a month in the Himalayas and climbing a small peak, I can offer some insights on this.

Do note that this applies only to those Himalayan (sub)ranges that are subject to the Indian subcontinent's monsoons.

1. Snow conditions

Pre-monsoon (=post-winter) the slopes still have the snow/ice deposited over the winter. The sun's heat has not yet reached high enough levels to melt much of it. So in general the snow/ice is harder. The risk of cornice avalanches is also higher because a lot of the snow deposited/accumulated on cornices is still there and not yet fallen off.

Post-monsoon (=post-summer) the summer has melted some of the winter snow/ice. Some of the snow is a little softer as well. This is somewhat analogous to how the snow is hard during the wee hours of the morning and gets softer over the day.

2. Glacial streams

Post monsoon, there will be more melt/run-off from the glaciers and little brooks of freshly molten glacier water crisscrossing the glaciers. The mountain streams typically have less water in the winter and pre-monsoon. Some small streams may even dry up in the cold because there is no melt water feeding into them.

3. Crevasses. This is important.

Pre-monsoon: The winter snow covers (superficially) a lot of the crevasses so they are hidden out of plain sight and not so obvious to spot. These so called hidden crevasses can be a significant objective hazard. You step on what you think is a regular snow covered surface only to discover that it is infact a thick layer of snow covering a crevasse and this layer of snow gives way under your weight. It takes a lot of observational skills and luck to accurately spot this sort of thing. Someone unfamiliar with the route won't actually be able to do it reliably.

The traditional glacier walk technique which involves probing the surface thrice with your ice ax may not be reliable depending on the depth and hardness of the snow covering the crevasse.

If you are lucky you just walk over it. If you are unlucky you fall into the crevasse.

Post-monsoon: The summer has melted much of the snow covering crevasses. So there are hardly any hidden crevasses. The open crevasses are obvious to spot. They sometimes ruin the view of beautiful white glacial fields and it can be scary and unsightly to look into the depths of a large crevasse. Open crevasses can also force a more roundabout route.