In 1999 we shared reports from the operational center of The Met. Office at Bracknell, UK. The reports must be tailor made and cost around 200 UsD each. The trouble was that small expeditions and independent climbers were charged the same cost as large expeditions, making the service more expensive for some. These years, there are reports made by many international met stations and subscribed to individually by expeditions, often on a sponsor basis. Share all reports and compare for best safety.
Get the forecast every third day or so from when you start climbing, and then every day on the summit days. The forecast will typically be done for 4-5 days ahead and more accurate the closer to the climb it is done. You need some basic knowledge to read the forecast:
Everest position is 28N and 87E. You need to bring a map to position the jet stream and various weather systems.
Read the table as follows:
Below is an example of two different forecasts, received in the spring of 1999, May 7 and May 28:
General Synopsis: A weak upper trough over Everest early in the day will move away to east, replaced by a ridge of high pressure.
Position of Jet stream in relation to Mt. Everest: Over Pakistan, SW 80kts, at first propagating east to lie over, or just north of, Everest, W 60kts, by the end of the day.
Cloud: Broken Cu building by day, with broken Ci throughout.
Weather: Mainly fair, small chance of a snow shower, especially later.
General Synopsis: Weak Upper Ridge just east of Everest, axis between 40N 95E & 30N 92E, with a broad trough to the west axis near 45N 75E to 32N 73E. Position of Jet stream in relation to Mt Everest: Jet well to the north of location between 45N 60E and 40N 92E. Core speed 95 knots near 39N 84E. Position of Monsoon: Invigoration of the Monsoon Trough in the Bay of Bengal, with the main activity as far north as 22N, but with an extension of this activity as far north as 30N further east (near 100E).
Cloud: BKN/OVC ACASCI, with ISOL CUCB.
Weather: Snow showers at upper levels.
Conclusions to be made from those reports:
May 7 is not a good day for climbing. Note the change from a trough to a region of high pressure. The jet wind is right at or very close to Everest and the wind on the summit (FL300) will be 57 knots.
On May 28 it's a totally different story. The jet wind is well to the north, the monsoon is moving and the wind is 10 knots! An excellent day for a summit attempt.
The weather reports provided by ExplorersWeb today are adjusted to climbers suggestions for improvement and easier to read, but you'll still have to understand and interpret the facts.
The second best weather source is the Sherpas. They normally have a great sense, especially for when not to climb. They have lived in the area for centuries and should always be listened to. However, their judgment might sometimes be somewhat biased and connected to overall motivation of climbing. Listen, think and make your own judgment.
Weather talk is one of the main topics with fellow climbers. Unfortunately, few actually read and try to understand the weather reports. Once again, listen, think and make your own judgment.