On 10 May 1996, severe thunderstorms struck the NE corner of the Indian sub-continent, including the Himalayas in Nepal. The storms spawned tornadoes and caused much damage and loss of life in India, Nepal and Bangladesh. On Mt. Everest, the thunderstorm resulted in the deaths of 10 climbers and was immortalized in Jon Krakauer’s “Into Thin Air”. During the pre-monsoon period thunderstorms occur almost daily in the Himalayan foothills, but not at elevations above 5000 m. For the storm in question, the lack of consistently accurate upper air data for the entire NE corner of the Indian sub-continent prevented detailed and precise calculations of wind, pressure and temperature fields and made the conventional stability indices such as CAPE and Lifted Index highly suspect. Thus, we used the NCAR reanalysis and NOAA/FSL data and our surface data from the Everest region to study the weather conditions preceding and during the 10 May storm. The known conditions for thunderstorm formation were identified: severe atmospheric instability caused by a deepening mid-tropospheric trough plus the sub-tropical jet stream overhead and abundant low-level moisture. In the High Himalayas, we identified unique conditions that combined to extend the depth of unstable air to permit thunderstorm initiation:

1. The sudden arrival of particularly cold air aloft.

2. A moisture supply from the east and southeast at low-levels and from the west at mid-levels.

3. Exceptionally dry air at low-levels to the south was incorporated in the morning up-valley flows causing a delay in convective cloud formation that permitted higher than normal surface temperatures at elevations above 5000 m.

We are currently studying a more recent May severe thunderstorm in the Everest region to determine if, once again, these unique conditions occurred. If they did, then they can be used along with the known thunderstorm-formation conditions to anticipate the formation of thunderstorms in the Everest region.