India, April 2 -- Thunderstorms and hailstorms battering northwest India this past week - unseasonal even by pre-summer standards - are the downstream effect of a disrupted polar jet stream and a shifting polar vortex that have driven an unusual surge in western disturbances, meteorologists said. March recorded eight western disturbances against a normal of five to six, and at least three more are expected through mid-April. "When the westerly jet stream is particularly wavy, we sometimes see an increase in the impact of the WDs in lower latitudes. The wavy jet stream is linked to rapid warming of the Arctic," said Mahesh Palawat, vice president, climate and meteorology, Skymet Weather. IMD has warned of light to moderate rainfall over nort...