AFTERNOON – OVERNIGHT: Partly cloudy skies remain in place across zone 6 and 7 in Illinois. There is even some patchy mist and fog being reported in some locations.
No rain showers are in place this morning across zones 6 and 7. However, through the afternoon a trough will move through. As it does, it will allow the environment to rise more and rain showers will start to develop after lunchtime across both zones.
Through the evening scattered showers will continue across Illinois. Some of these showers will produce some brief down pours of rain. With temperatures aloft so cold, some small hail can’t be ruled out within the better organized areas of rain. By 4-5 PM scattered areas of rain will still be in place across the area.
Scattered areas of rain will remain possible through the evening, but once we lose the sunshine and the upper-level trough moves out showers will quickly diminish. By 9-10 PM only a few isolated light showers will remain across the forecast area.
Overnight a cold front will start to sweep to the south and southeast across Illinois. Along the front rain and perhaps an isolated t’storm will develop. By 3-4 AM that line of rain will be entering northern zone 7 as it continues south and southeast.
Lows overnight will be in the mid 40’s north to around 50 south.
WEDNESDAY: Through the morning hours on Wednesday the cold front and rain will continue to the south across the zone forecast area. By 7-8 AM the front looks to be located across zone 6 south of I-70. Along the front rain will still occurring, with perhaps a few rumbles of thunder mixing in.
The cold front and rain will move off to the southeast through the morning. By 12-1 PM Wednesday isolated showers will still be in place.
Through the evening the NAM 4 km only depicts the chance of some isolated light showers. However, there will be an upper-level piece of energy that spins around the back side of the surface low through the evening. By 4-7 PM this will likely increase the chance for rain across Illinois once again.
With the upper-level low right on top of the region and upper-level temperatures being so cold. Once again, some small hail can’t be ruled Wednesday with some of the better areas of rainfall.
Highs on Wednesday will be in the mid 50’s north to upper 60’s south. Winds will be very strong at times on Wednesday with gusts from the north at 35-45 mph.
Through the evening into the overnight the disturbance will move out of the region. However, there will still be some upper-level vorticity around, so perhaps some stray light showers will through the early to mid-overnight hours.
Lows will be in the upper 30s north to mid 40’s south.
New rainfall totals across most of zone 6 and 7 will be less than .25”. However, across eastern Illinois some localized .25-.50” reports will be possible.
THURSDAY: By early Thursday morning the upper-level low will be moving off to the east. As it does, an area of high pressure will be building into the region.
This will allow for drier air to working into the forecast zones. As the dry air works in, clouds will erode giving way to sunshine throughout the daytime hours on Thursday.
With drier air and clearing skies it will help temperatures rebound. Highs on Thursday will be in the low to mid 60’s across the area. There will be some breezy winds on Thursday with gusts of 20-30 mph possible at times.
FRIDAY: At the surface the area of high pressure will continue on Friday. This will allow sunny and dry conditions to remain to end the week.
At the upper-level a ridge of high pressure will be building in. Not only will this reinforce the dry air, but it will also allow warmer air to expand northward, so temperatures are expected to further increase by the end of the workweek.
Highs on Friday will be in the 70’s.
WEEKEND: The upper-level ridge looks to break down through the day on Saturday. This would allow a cold front to swing through Saturday afternoon into the evening hours. Along the front rain and t’storms will move quickly southward through afternoon and evening.
Highs on Saturday will be in the mid 70’s to low 80’s across the area. Of course temperatures will be dependent on timing of the front and the amount of sunshine that is realized.
While the atmosphere doesn’t look overly impressive Saturday, some moderate instability coupled with some “stronger” winds aloft may allow some strong to severe storms develop. However, details are very fuzzy right now and that’s a threat we will have to fine-tune through the week if needed.
SUNDAY: Model guidance is suggestive that the front stalls out across southern portions of the zone Saturday into Sunday. This would allow for rain to continue overnight Saturday into Sunday.
However, models are not in agreement with the timing and placement of an area of high pressure on Sunday. While the GFS and CMC bring it in directly over the region, the EURO keeps it farther north.
Just going off of the current pattern, I would think the front will indeed stall in southern zones Sat night into Sunday. The high will build in across northern Indiana/Illinois Sunday. Isolated to scattered rain/storm chances will be possible across southern portions of the zone forecast area on Sunday. Overall, we will have to see how things play out and we will fine-tune the forecast as we get closer to the weekend.