Kathmandu, May 14 -- Unpredictable weather patterns are shrinking the summit window for Everest climbers this spring, agin stoking fears of overcrowding on the world's highest peak. Despite the second-highest number of permits ever issued, many teams remain put at base camp, awaiting safer conditions.

Expedition operators warn that if the narrow weather window continues to contract, a repeat of past traffic jams-where climbers are forced to wait in line in the 'death zone' above 8,000 meters-could become inevitable.

"This season doesn't look promising," said Pemba Sherpa, executive director of 8K Expedition, which has been assigned the critical rope-fixing task from Camp II to the summit. "It's been five days since the route opened, but...