Subfreezing temperatures and fog combined with millions of gallons of water to create curtains of ice on the Roosevelt Apartments, which was destroyed in a fire Thursday morning. The fog, produced by a high-pressure system, made Salt Lake's Friday high of 24 degrees seem colder and kept air quality in the unhealthy zone. A health advisory continues for downtown Salt Lake City and the state's residential areas, and pollution is predicted to increase. People with existing heart or respiratory ailments should reduce their exertion and outdoor activities, and unnecessary driving and non-essential use of wood-burning stoves should be curtailed. Forecasters expect fog through the weekend, with snow possible by Sunday. Highs will be in the upper 20s with lows in the teens.