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ExWeb series - Winter climbing: The BAD chart, part 3
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Dec 19, 2004 19: 46 EST
Lately we've run a series about winter climbing in Himalaya. In high mountaineering, there are two ways to define winter; “calendar” and “permit”. The Calendar winter starts December 21, whilst a winter climbing permit begins December 1.

The Calendar winter is considered a "classic winter" climb. All first winter accents of 8000ers were made by Polish climbers - in Calendar winter. The first ascent was on Everest in 1980 and the latest on Lhotse in 1988.

But still, what does the reality look like? Let's put calendars and permits aside for a while, and examine the weather only, in order to find the worst time to climb.

Very few people have climbed 8000ers in the winter, and no one has skied to the North Pole or the South Pole in the cold season. This series is divided in 4 parts:

1. Wind Force

2. Temperature, Wind-Chill

3. Humidity

4. The “Bad” Chart – Defining Seasons

Today, part 3: Humidity

Nepal and Everest have a very distinct wet season characterized by almost daily precipitation and very little wind. The monsoon arrives at Everest by the second week of June and ends in the beginning of October.

Understanding humidity levels

High humidity % indicates high risk of snow/rain. Several factors, such as temperature and barometric pressure, decide if a certain humidity level will result in actual precipitation (rain or snow). But to simplify; at 0-40% there is a very small chance of snow fall. Above 50% there is a chance of snow. At 80% there is a very high chance of snow fall. Almost all precipitation on Everest is in the form of snow.

Humidity at Everest Summit

The summit of Everest is predominantly dry. Typically expeditions in Base Camp and Camp 2 report snow and bad weather while climbers higher up have blue skies. It can be a good bet to climb from BC if the weather forecasts are looking good, even if the weather outside the tent looks gloomy. Chances are you'll hit good weather by the time you are at the top of the ice fall or the North col.

October, November and May are the driest months. Check the picture of a snow covered Everest North Face in August 2003.

Humidity at Everest Base Camp

Seasonal humidity differences are much more dramatic at lower elevations. Everest Base Camp will get some snow or rain pretty much every day from June to early October - when precipitation comes to an abrupt halt. Remains of October and all of November are very dry, followed by a slight monthly increase in snowfall over the winter months.

The humidity level is one of the few (only) positive factors for a Himalayan winter expedition. Expeditions to very avalanche prone mountains thus sometimes choose this period for their climb. This was the strategy of Anatoli Boukreev, who nevertheless sadly was swept away by an avalanche on Annapurna Christmas day 1997.

Tomorrow Tuesday: 4. The “Bad” Chart – Defining Seasons

Image 1 (ExplorersWeb): Humidity at Everest Summit since 2002.
Image 2 (Everest Snowboard Expedition 2003): Snow covered Everest north face during Monsoon season - August
Image 3 (ExplorersWeb): Humidity at Everest Base Camp since 2002

Data
"BaseCamp" is at Pressure (hPa) 495 or app. 6100m of altitude

"Summit" is at Pressure (hPa) 346 or app. 8750m of altitude

The charts are based on forecasts delivered by SMHI and compiled by the super-computer at ECMWF. The information below is compiled from 868 forecasts from May 1 2002 to Nov 1 2004.

There is no weather station at the Summit of Everest which would have allowed exact readings, but the forecast should be fairly accurate - as it has been used by climbers for 10 Himalayan seasons and hundreds of high-altitude expeditions.

The AdventureWeather 8000 meter forecasting project is free of charge to climbers and sponsored by ExplorersWeb.com and its partners.

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