The Observatory issued its first frost warning of the year yesterday, with temperatures expected to fall as low as seven degrees Celsius overnight. Forecasters expect the cold spell to last until the weekend, with Saturday seeing temperatures of between 12 to 16 degrees. But they could fall back below 10 degrees early next week. The cold weather warning was also in force last night. The SAR experienced its coldest day in eight years on December 23 when temperatures dropped to 5.8 degrees in urban areas and minus 2.8 degrees on Tai Mo Shan.