New Delhi, Nov 4 : Delhi-NCR witnessed the season's first fog with both the IGI and Safdarjung Airports reporting poor visibility with significant reduction to the range of 600-800 metres on Thursday between 7 a.m. and 11 a.m. According to India Meteorological Department (IMD), visibility during the same period on Wednesday was at range of 1,500-2,000 metres in mist/smog. "This (fog spell) has been due to calm/light wind prevailed during this period and presence of higher humidity in the range of 88-95 per cent," the IMD's R.K. Jenamani said. Such shallow to moderate fog likely to occur mainly in the morning hours till Saturday and reduce thereafter due to likely strengthening of the winds over the region from the same day noon/afternoon, he said. In deep winters, fog season means less and less visibility and especially for airports, means diversion of flights. On the highways, dense fog results in accidents, many of them resulting in fatalities. /IANS