We continue to lose daylight in the northern hemisphere as we move through fall, allowing colder air to build in northern Canada with the lower sun angle. The cold air will gradually work it's way farther south, entering the United States more frequently over the next few weeks. Periods of warm weather tend to be short-lived during the fall with increasing hits of cold air as we head toward winter. Also, longer, cooler nights often lead to dense fog formation.
Medium range forecast models show a progressive weather pattern through the first week of October with waves of low pressure aloft moving in from the west. Rain and cooler air will move in this weekend followed by a slow warming trend early next week. Another chance of rain with cooler air is expected to move in later next week.