Friday, by most standards, was another cloudy, dreary day in Chicago. However, for about 80 minutes during the morning, the city recorded its first official sunshine in more than a week. The day’s official tally was just a dismal 13 percent of the possible sunshine, but it is a harbinger of a sunny and very mild Sunday. A surge of mild Pacific air should chase away the persistent cloud cover, allowing temperatures to surge to near record levels Sunday afternoon, threatening the day’s record high of 51, established in 1992. The delightful weather will be short-lived as cloudiness and chillier conditions return by Tuesday, which in conjunction with a series of weather disturbances will bring an increasing threat for a significant snowfall or a wintry mix Tuesday night and Wednesday. Seasonably cold weather will follow in the wake of the storm through the end of next week.