Oct. 19--Warmth returns this week after a weekend frost in the Chicago area and the season's first accumulation of snow in the upper Great Lakes.
Temperatures are expected to rise over 40 degrees from Sunday's subfreezing lows to Monday afternoon's September-level 70s.
Cool weather that marked the start of October was followed by a stretch of 11 days with readings at or above normal.
After a three-day cool snap, another prolonged period of warmth begins Monday and is expected to last through Saturday.
This cycle of mild, dry weather, punctuated by brief intrusions of polar air, is likely to continue into the winter months based on the strength of this year's El Nino pattern.
