Our two week dry stretch came to an end Sunday following the passage of a cold front early in the morning. A band of rain developed behind the front Sunday afternoon and will continue through Monday morning. A strong trough of low pressure still west of the Mississippi River is the driving force behind much of the rain and that trough won’t pass through northern Illinois until a little after sunrise Monday.
The unsettled pattern is set to continue through the end of September and into the beginning of October as a deep trough of low pressure continues to build over much of the Midwest, Great Lakes and Northeast. Within the trough – or dip in the jet stream – there are several ‘mini’ low pressure systems that will move down the western edge. Each passing low will not only bring a chance for scattered showers, but also help to pull down a much cooler air mass. Highs on Monday are only expected to warm into the low 60s. Scattered showers will be possible during the first half of the day Monday, but we should dry out by Monday evening.
Tuesday and Wednesday will feature only a slight chance for showers but we will see that chance increase Thursday as an even stronger push of cold air arrives Thursday afternoon. This will limit high temperatures during the afternoon to the 50s. Thursday night will be chilly with lows area wide dipping into the 30s. However, cloud cover may keep the frost risk limited into Friday morning. Highs on Friday look to only climb into the low 50s. High pressure moving in Friday night and Saturday morning could increase our chance for more widespread frost, and even a freeze, Saturday morning. Highs Saturday afternoon look to warm only in the upper 50s.