AFTERNOON-OVERNIGHT: A cold front remains in place across western Illinois this morning, but is moving off to the east. To the south of zone 6 an area of more extensive rain coverage is in place. This is thanks to weak area of low pressure that is moving along the cold front this morning.
The cold front will continue to advance to the east this morning. As it does, the low will slowly move along the front to the south of the region. This may slow the overall progression of the cold front.
By 12-1 PM rain and storms will be moving across zones 6 and 7. A couple of those storms could be on the strong side across southern Illinois early this afternoon.
Through the afternoon rain and storms will continue across eastern portions of zones 6 and 7, this with better rain chances remaining across zone 6. By 4-5 pm the cold front will be pushing out of the state along with the rain and t’storms.
Through the evening it does look like skies will start to clear from west to east. The latest HRRR model does show the quick clearing behind the front this evening as drier air moves in.
Some heavy rainfall will be possible across the forecast zones this afternoon and into the evening. The latest HRRR and RPM models both suggest areas of 1.75-2.5” of new rainfall through this evening. So heavy rain and some localized flash flooding will be possible in areas.
Through the overnight an area of high pressure will ridge into the forecast area allowing for skies to remain clear.
Lows overnight will be in the upper 40’s to mid 50’s.
FRIDAY: An area of high pressure will be in control to start the day on Friday. This will lead to mostly sunny skies through at least early afternoon on Friday.
Highs on Friday will be in the upper 60’s to mid 70’s.
However, to the north a cold front will be pushing to the southeast. Along this front rain and storms will form and move across the state.
By 4-5 PM a line of storms will be in place to the north and northwest of zones 6 and 7 along the cold front.
Through the evening that line will continue off to the southeast along with the front. By 10-11 PM storms will be moving into zone 7.
Through the evening into the overnight storms will continue to the southeast. However, I do think they will weaken as they get into zone 6 by 1-2 AM Saturday morning.
Through the overnight rain and storms chances will fade with only some scattered areas of rain and perhaps a couple t’storms remaining.
I do think severe weather will be possible tomorrow across northern Illinois and perhaps as far south as zone 7.
Strong winds at 500 mb and strong 850 mb winds of 55-65 mph would be plenty sufficient for organized severe weather.
However, both moisture and dew points look to be lacking. Dew points will be generally in the mid to upper 50’s on Friday with perhaps a ribbon of 60-62° dew points along the front to the north.
While it will be sunny most of the day, the lack of widespread moisture will really limit the amount of instability that is available. Isolated areas of 750-1100 J/Kg of CAPE are forecast to occur tomorrow afternoon along the front.
With that being said, I do think severe weather is possible, primarily north of the zones 6 and 7. However, pending actual moisture and instability, zone 7 could see some strong to severe storms as well. Main risks would be damaging winds and hail. However, a couple isolated tornadoes will be possible too. We will fine-tune the chances in the coming 24 hours.
By 3-4 AM Saturday morning the cold front will be out of Illinois and only a few showers will linger.
Lows Friday night into Saturday will be in the mid 40’s north to mid 50’s south.
SATURDAY: Behind the front an area of high pressure will build into the area on Saturday. As it does, drier air will work in and clouds will thin out.
However, with the high pressure system in place cool temperatures will be locked in for the day. Highs on Saturday will be in the mid 50’s north to low 60s south. Winds will be breezy at times with gusts of 20-25 mph possible.
Saturday night skies will be clear to mostly clear across zones 6 and 7. This will allow temperatures to really cool overnight. Lows will dip in to the mid 30’s to low 40’s. It is not out of the question that there could be some frost, especially across northern zone 6 and zone 7.
SUNDAY: The area of high pressure will move over the top of the region on Sunday. I do think this will lead to mostly to partly sunny skies across the forecast area.
However, with a bit of a disturbance moving through aloft Sunday afternoon clouds may increase a little and a stray rain shower could develop. However, right now this looks to occur north of the region, so don’t cancel any weekend plans over it.
Highs on Sunday will be around 60 north to the mid 60’s south.
MONDAY-TUESDAY: The area of high pressure will move off to the region east on Monday. However, it looks to be in control of the weather through at least mid-day. This should allow most of Monday to remain nice.
However, an area of low pressure will be moving in from the south and southwest. This will allow rain chances to increase late Monday afternoon into the overnight.
Highs on Monday will be in the low to mid 60’s.
Rain and storms will remain possible on Tuesday. However, models are not agreeing on coverage and timing. The GFS is much more aggressive with heavy rain and t’storms Monday night and Tuesday.
However, the EURO model develops a break in the precipitation Tuesday giving us some dry time. Then by evening more areas of rain develop and move into the forecast zones.
This area of heavy rain and storms will really come down to the location of the warm/stationary front, because that will be the focal point for rain/trom development. These front can be very tricky to forecast just 24-36 hours out, so it’s something we will have to fine-tune for you as we get closer to the forecast period.
7 DAY FORECAST( TEMPERATURES VARY USUALLY COOLER NORTH TO WARMER SOUTH)