Cooler Temperatures and Rain Expected for the Weekend

Temperatures Thursday afternoon warmed into the low to mid 70's area wide under a partly cloudy sky.  But the warmth we've felt for the first 10 days of the month is about to change.  And it's all because of a cold front that passed early Thursday morning.

Surface winds have shifted around to the northeast this evening as high pressure settles further south into the Great Lakes.  The northeast breeze will bring temperatures down into the 40's overnight but keep highs only in the 50's Friday!


Winds will remain from the east during the afternoon Friday as a stationary boundary sits just south of the immediate Stateline.  Temperatures south of the boundary will warm into the 80's over central and southern Illinois.  It's possible that some of our southern counties of Whiteside, Lee and DeKalb could have temperatures reach the 60's as they are closer to where the boundary will lie.


Light showers have developed to the northwest of Illinois and are now beginning to move into southwest Wisconsin.  There could be a quick passing shower along and north of Highway 20 this evening, but a better chance for rain will come during the overnight.

The rain tonight will be a result of warm air coming in from the southwest but nearly 3,000ft above the surface of the earth.  This is what is known as 'warm air advection showers'.  Because the arrival of the warm air is causing the rain to develop.  There is also a disturbance moving through the jet stream from the west helping the air to rise and produce the rain showers.


Jet stream winds will remain over northern Illinois and southern Wisconsin over the weekend which will keep the weather pattern fairly stagnant through early next week.  This is also part of the reason why the frontal boundary won't move much through Sunday.  Unfortunately with a near parallel flow in the atmosphere it sets up an opportunity for repeated rounds of rainfall through Sunday night.


It looks right now that the heaviest rain will fall over southern and central Wisconsin.  There, over two inches of rain could occur through early next week.  Closer to northern Illinois an inch to an inch and a half of rain may fall.