The month of October is known for its big pattern changes with temperatures reaching the mid 70s one afternoon, quickly dropping into the low 30s the next night. We could experience that very change by the end of the week as a strong cold front moves through the middle of the country.
High pressure will keep our skies mostly clear with temperatures gradually warming through the mid and upper 60s Monday, Tuesday and Wednesday. Temperatures Thursday afternoon have a chance of reaching the low 70s, but clouds and incoming rain could cause us to fall short before reaching that mark. A big dip, known as a trough, in the jet stream will develop out over the Rockies late Tuesday night into Wednesday. Low pressure will develop, as a result at the surface, traveling through the central Plains Wednesday into Thursday before lifting into the Upper Midwest and Great Lakes Friday and Saturday. Ahead of the low, strong southerly winds will push a warm and moisture rich air mass northward. Behind the low a very cold air mass will fall across the Rockies and northern Plains, bringing snow to the northern Rockies and possibly the season’s first snowfall to the northern Plains.
Closer to home, rain showers will expand northward Thursday with the possibility for thunderstorms (some perhaps strong) Friday afternoon. Late in the afternoon and evening a strong cold front is expected to move through from west to east. Temperatures will fall from the 60s and 70s Friday, quickly into the 30s by Saturday morning. Wind and cloud cover will likely prevent any frost from forming and limit how far our temperatures fall, but Saturday night temperatures could tumble close to the freezing mark. On average, northern Illinois usually experiences its first first (32 degrees) within the first week and half of the month, with a killing freeze within the first two and a half weeks. Highs Saturday and Sunday may not even make it out of the 40s depending on overall cloud cover. Wind-driven showers may also occur, especially Saturday, as low pressure spins over Wisconsin.