AFTERNOON-OVERNIGHT: Skies have started off clear across Illinois thanks to an area of high pressure that is has ridged into the state. However, the main story will be cold front that will be approaching the forecast area from the northwest throughout the daytime hours.
While skies will remain clear in most locations through early afternoon, clouds will be on the increase ahead of the southeasterly advancing cold front. As we progress through the afternoon skies will start to cloud up from northwest to southeast.
Dry conditions will persist through the afternoon into the evening across zones 6 and 7. However, by 6-7 PM storms will be working in from the northwest, entering western and northern zones 7 at this time.
Through the evening storms will continue to work their way southeast across Illinois. By 10-11 PM rain and storms will be ongoing across both zones 6 and 7. This as the cold front swings across portions of western Illinois.
Through the overnight leftover rain and storms will weaken as we lose daytime heating. By 3-4 AM the cold front will push out of the Illinois taking any precipitation with it.
I do think strong to severe storms will be possible across zones 7 and perhaps zone 6 later this evening into the overnight. However, moisture will be a big limitation today. Dew Points are really lacking with this system coming in from the north. A small ribbon of moisture is forecast to move into western/northern Illinois later this afternoon, so that should contribute somewhat to severe weather chances.
Winds aloft today into the evening will be impressive with 500 mb flow of 65-80 mph and 850 mb winds of 40-50 mph, winds shear to support better organized storms will certainly not be lacking.
While I do think the best severe weather chances will be north of the region, it may extend far enough south for portions of zone 7 to be included in that risk. With impressive amounts of wind shear later on this evening I can’t rule out a few severe storms southward into zone 6 , although the threat will not be as great. Initially hail, damaging winds, and few tornadoes will be possible. However, through the late evening the main threats will be damaging winds and some hail as the tornado threat will decrease.
New rainfall totals through late tonight will average .10-.30″. it looks like heavier totals will be across northern zone 6 and zone 7 where storms will be more intense. In those locations, some .50-1″ total can’t be ruled out locally.
Lows overnight will be in the mid 40’s north to mid 50’s south.
SATURDAY: An area of high pressure will start to build in from the west on Saturday. This will help some of the clouds to clear out of the area. It looks like western and central portions of the zones will see more sunshine, while clouds do stick around across eastern Illinois.
Highs on Saturday will be in the mid 50’s north to low 60’s south. Some winds Saturday could be strong with gusts of 20-30 mph possible.
High pressure will remain in control Saturday night into Sunday. With clear skies and lessening winds, temperatures will really drop off overnight.
Lows Saturday night into Sunday will fall into the mid 30’s north to mid 40’s south. With overnight temperatures being so cold, some frost will become likely the farther north you go.
SUNDAY: High pressure will remain in control of the weather on Sunday. This will allow sunny to mostly sunny skies to remain. The only place that could see some clouds Sunday afternoon would be across southern zones, closer to a weather system in place south of the forecast area.
Highs on Sunday will be a tad warmer than Saturday with temperatures warming into the low to mid 60’s.
MONDAY: High pressure will be in control of the weather to start the week. However, through the day it will move off to the east.
As the high pressure moves out of the forecast area clouds will be on the increase ahead of the next rain maker. In fact, a few isolated showers may be possible through the day on Monday across southern zone 6.
While rain chances through the day on Monday look pretty small, better chances will emerge as we get later into the evening. Right now both the EURO and the GFS show better rain chances spreading across Illinois overnight Monday into Tuesday.
Highs on Monday will be in the upper 50’s to mid 60’s.
TUESDAY- WEDNESDAY: Rain and t’storm chances will continue through the day on Tuesday. This will be thanks to a stationary/warm front that will remain in the area. While the exact placement of the front will have to be fine-tuned, I won’t be shocked to see some localized areas of heavy rain next week where the front does stall out.
Both the GFS and the EURO are in pretty good agreement that high pressure will build in Tuesday night into Wednesday as the surface low moves away from the region taking the front with it
As the high builds in through the day on Wednesday it would allow skies to clear and even bring the temperatures up a bit. Highs by mid next week are forecast to be back into the low 60’s to low 70’s.
LONG-RANGE: Farther into next week models are in pretty good consensus that the area of high pressure will slowly move to the east WED-FRI. Not only will it allow for drier conditions, but will also help moderate temperatures a bit every day.
7 DAY FORECAST (TEMPERATURES VARY SOUTH TO NORTH GENERALLY COOLER NORTH TO WARMER SOUTH)