A Pattern Change This Week

The last weekend of summer proved to be a fabulous one.  There was lots of sunshine, and temperatures reached the low 80's on Saturday and the upper 70's on Sunday.  A strong cold front is approaching from the northwest tonight, and will pass through the Stateline around noon on Monday ushering much colder air into the mid west.   In advance of the cold front tonight, clear skies will slowly become partly cloudy.  It will not be a cool as the last two night's with a low around 55 degrees.  Monday will be mostly cloudy, and there could be some scattered showers in the morning.  There is no gulf air available for the front to work on, so rain amounts are expected to be relatively light... around 0.25" or so.  There could be an isolated thunderstorm or two with the passage of the front because of unstable conditions with very cold air aloft with the passage of the front.  High temperatures around 73 degrees will occur around noon, the wind will switch to the northwest at 10-20 mph, and temperatures will fall during the afternoon as colder air follows in behind the front.  Some scattered light showers could linger until around midnight, skies will become  partly cloudy, and it will be colder with a low in the low 40's.  A large area of Canadian high pressure will be  centered near Sioux City, Iowa by 6 am on Tuesday.  A brisk northwesterly wind will hold temperatures in the 50's for most of the day under sunny skies.  The high temperature may reach 60 degrees in Rockford on Tuesday afternoon.  It will be clear and cold on Tuesday night as the high pressure  moves to near Quincy, Illinois by 6 am Wednesday morning.  With the core of the cold high very nearby, clear skies, and light winds, there will be maximum radiational cooling during the night dropping temperatures across the Stateline into the middle 30's, which is likely to cause some early season patchy frost.  Any frost that does occur will likely be in low lying rural areas, but may edge into some small cities.  Full sunshine during the morning will cause a nice rise in temperatures, and by afternoon it may be as mild as 68 degrees in the Rockford area.  There will be an increase in clouds by late in the afternoon as the next system dropping down in the fast northwesterly upper air flow approaches the Stateline.  Scattered showers may develop on Wednesday night in advance of the front.  The low will be in the low 50's. The next cool front will sweep across the area early on Thursday morning, and there could be some scattered light showers on Thursday.  Another front will move into the area early on Friday with a good chance of more light rain showers. Temperatures will drop to the mid 40's for overnight lows next weekend, and rise to the middle 60's.  Below average temperatures area expected to continue for the rest of September.