Much cooler air is common to start the week in much of the central third of the U.S. while the 80s and 90s are more common west of the Rocky Mountains. Patchy frost is likely in the northwestern Plains and into the western and central Corn Belt by midweek, as light rainfall delivered by a series of low-pressure systems moves through the region, potentially slowing fall harvest progress. USDA will release its weekly Crop Progress report this afternoon and will show the harvest strides of the last week. See more on the latest weather outlook here.