Low clouds on Monday persisted much of the day, limiting area temperatures to the low 40s at most locations. The high of 40 degrees at O’Hare airport was 10 degrees below normal. Cold temperatures have been common the opening 2 weeks of November, the coldest such period in 21 years. Milder air is to make its way into the region in coming days, though readings are still expected to average at, or slightly below normal. Temperatures are likely to spike Friday, when a deepening storm system is to sweep 50-degree air into the region. Thunderstorms may accompany a strong cold front late Friday, and the Storm Prediction Center has highlighted the metro area for a risk of severe weather. Temperatures are then forecast to plummet, with highs by Sunday struggling to reach freezing.