Mt. Everest Weather Forecasting
Weather Mt. Everest & Himalaya
Mount Everest is located in the normal elevation in which the jet stream is located so winds during much of year exceed 80 mph (128 km/hr.). Remember, hurricane force winds are at 74 mph (118 km/hr.) or greater. During the winter months the subtropical jet is aimed over Mt. Everest bringing these strong winds. If the polar jet, which is normally located close to 50 degrees latitude, dips to the south and merges with the subtropical jet, Mt. Everest and the rest of the Himalaya can get some extreme winds of well over 125 mph (200 km/hr).
The big question for climbers of Mt Everest and the other major 8000 meter (over 26,400’) peaks is the timing of the weather patterns which bring reasonable winds for climbing (usually 25 mph or less). Starting in March and April we begin to see a minor reduction in the winds, but this is more likely in May. What usually happens in May is the polar jet begins to shift to the north and the subtropical jet starts to weaken. Sometimes there is short window early in May of reasonable winds. However, it is more likely that we get a weather window of 3 to 5 days of reasonable winds sometime during the last two weeks of May. However, the jet will still meander back and forth, and that weather window for climbing Everest can quickly close.
Usually by June ,or sometimes later in May, we start to see a major shift in the wind patterns as they become more from the south or east bringing moisture into the region. Once these winds get established, that is usually the start of the monsoon season. This usually runs from the middle of June to September. During the monsoon season the heavy precipitation will keep most climbers and trekkers out of the region.
In September, as the monsoon and associated heavy precipitation starts to “slowly” retreat trekkers and climbers return. Although Everest is not generally climbed in the fall, many of the other 8000 meter peaks, such as Cho Oyu, Makalu, Manaslu, and Shishapangma, are climbed by some. Generally by late September and early October there is less moisture and reasonable summit winds, so that is a popular time. However the region is still subject to cyclones moving in from the Bay of Bengal. More on that later.
By November, the polar jet starts to drop down from the north and the subtropical jet starts to reestablish its position near Mt. Everest and the rest of the Himalaya. At this point we start to see an increase in winds but with generally less moisture. Even in November, some of the major peaks are still climbed, especially since the moisture is limited. But winds can still be an issue.
Photo above are winds in at about 36,000 foot level 10,909 meters) at over 140 mph (224 km/hr.)
Weather & Trekking in the Himalaya
Many types of treks in the fall bring folks to the Himalaya region. One popular region is Everest Basecamp and other treks which do not require one to go over major passes; thus the weather is “usually” not a major issue. There is an exception when a strong cyclone moves in from the Bay of Bengal and makes the unusual direct hit. Fortunately, this is an uncommon occurrence.
These big storms can occur during the post monsoon season, especially in October or November. One such storm made a direct hit in the Annapurna Circuit area in October of 2014 (see article in which we are quoted). These big snow storms certainly do not occur every season and are actually classified as unusual. However, trekkers should certainly have a means of monitoring the big storms that are possible in the trekking regions. We at Everest Weather provide these types of forecasts for trekkers.
(AP Photo/U.S. Navy Joint Typhoon Warning Center, Friday Oct. 11, 2013) | Source http://news.yahoo.com/look-devastating-cyclones-bay-bengal-091035846.html
By November the weather in the trekking areas in the Himalayan region usually brings sunny and mild afternoons. Although, it is cold at nights.
March, April and May are usually mild and dry in the trekking areas. However, by May weather patterns start to change as the monsoon slowly begins to approach many of the trekking areas. Also, the tropical cyclones begin to form in May so one needs to monitor for big storms.
You are at basecamp (about 18,000’) and acclimated and ready for a summit bid. You want a 7 day forecast to determine a good summit weather window. Low winds and little to no snowfall. Easy forecast right? Yes and no. The shorter term forecasts out to 3 days have become more accurate, especially in terms of the winds. It is the extended forecasts out to 5 to7 days can provide some difficulty. It really depends on the trends of the models and having the experience to discern which forecast model to lean on.
Why use Everest Weather? We have been providing custom forecasts for the Mt. Everest area since 2003 for both small groups and large expeditions (see some of our clients).
Our two lead forecasts each have over 25 years of experience in worldwide forecasting. We review and analyze a minimum of 6 forecast models and many more at times. Many other weather forecasters simply run automated computer models that give data output for Everest. The main drawback of this approach is that these automated computer models are not looking at the big picture. The big picture being the weather dynamics involved: major troughs, location and placement of the jet stream, formation of any cyclones in the Bay of Bengal, and progression of the monsoon to name a few.
We review the automated computer model output then bring analysis to see if these forecasts are consistent with the big weather picture. After each forecast, we get real time weather observations from clients and are able to assign a high weighted average to the forecast model that is the most accurate.
Finally, Michael Fagin is an active mountaineer. Although not a technical climber or climbing any of major peaks, he understands mountain weather. As we all know, most mountains generate their own weather patterns and Michael field tests this on a regular basis. And Michael knows how critical accurate forecasts are to mountaineers.