Scientists suspect that the reason is air pollution caused by factories and commuter's cars.
The pollution builds toward the weekend, increasing the chances of rain, then clears after a two-day break from pollution sources, resulting in fairer weather. Snowfall will be below normal, with the best chance for snow in mid-January in the northern interior. The stormiest weather will occur in mid and late January and the first half of March. April and May will be cooler than normal, especially in the north. Rainfall will be near or below normal in the west and above normal in the east.