A very slow-moving weather pattern has developed across the central United States. For the Chicago area, this means the cool and dry conditions that prevailed on Monday will persist Tuesday and Wednesday, then give way to warmer temperatures into the weekend and beyond. Readings plunged 17 degrees from Sunday’s official high of 92 to Monday’s 75 (registered early in the day), but temperatures far south and southwest soared to a second day of 90-degree readings before the cool air arrived. Marseilles reached 91 degrees. Highs are forecast to remain in the 70s Tuesday and Wednesday (but cooler conditions can be expected within a mile or two of Lake Michigan), then a major warmup begins Thursday and continues for several days. Present indications suggest a multi-day string of 90s for Chicago, beginning on Sunday.