AFTERNOON-EVENING: A stationary front remains in place across southern Illinois this morning. That has contributed to morning rain across the forecast zones, especially zone 6.
Through the morning hours the front will likely remain stationary across southern Illinois. However, this front will start to lift northward today as a warm front. As the front does lift northward rain and storms will develop along the front. By 12-1 PM scattered rain and some storms will be in place across the forecast area.
This evening the front will lift to the north of the area. However, rain and storm chances will continue in the warm sector. By 4-5 PM scattered rain and storms look to be ongoing across Illinois.
Through the evening we will be watching a developing line of storms to the west of the region. By 8-10 PM this line will be moving east into the forecast area. If the line can stay together into the evening then the threat for some strong to severe storms isn’t out of the question later this evening, with strong winds and hail the main concerns.
Through the overnight those and other scattered storms should weaken as we lose daytime heating. As instability fades so should coverage and intensity of any remaining rain/storms.
Lows overnight will be in the low to mid 60’s.
TUESDAY: Some isolated to widely scattered rain and storms will remain in place early on Tuesday. By 7-8 AM the NAM 4km picks these up well.
By 12-1 PM Tuesday afternoon the warm front will remain in place across northern Illinois. By this time the front maybe becoming stationary for the time. Regardless, with the front around, some isolated rain/storms can’t be ruled out. However, it appears clouds will be sticking around, so that will limit daytime heating/instability and any better t’storm coverage.
Through the afternoon we will see some clearing across southern Illinois. This should allow for some instability to build across southern zone 6. The latest models suggest 2500-3500 J/Kg of CAPE will be possible across southern/southwestern zone 6. IF clearing should occur farther north than anticipated, then higher instability values could be realized farther north.
Highs on Tuesday will be in the low to upper 70’s. Winds will be gusty at times with 30-35 mph wind gusts possible.
While a few isolated showers or storms will remain possibly though the afternoon Tuesday, I do think there will be dry time. By 6-7 PM Tuesday evening a few t’storms will develop closer to the warm/stationary front across northern zone 7.
However, by 9-10 PM t’storms will develop across southern Illinois where the higher instability values and a surface boundary will be in place.
While winds at the upper-levels will not be overly impressive, they will still be enough to support at least the threat for severe weather. With westerly winds at 500 mb coming in at 45-55 mph and south-westerly winds at 850 mb coming in at 30-40 mph, there will be enough shear to create some severe thunderstorms.
Through evening into the overnight thunderstorms will continue moving off to the east and southeast. While there could be a threat of a developing cluster of severe storms later into the overnight, it is still a bit unclear exactly where this would occur, so it’s something we will have to fine tune over the next 24 hours.
Regardless, the risk for severe weather will be in place across zone 6 tomorrow and possibly northward if more instability can be realized. Main risks will be damaging winds, hail, and a couple of tornadoes.
Through the overnight into Wednesday storms will move out of the region and it will setup for a dry start to Wednesday.
Lows Tuesday night will be in the upper 50’s north to mid 60’s south.
WEDNESDAY: An area of low pressure will be to the regions west on Wednesday. However, it does look like it’s influence on our weather through the day will be relatively minimal as the rain associated with the low will stay to the west for most of the day, with only slight chances for rain/storms across very southern zone 6.
Highs on Wednesday will be in the mid 70’s to mid 80’s across the area.
To the west of the region we will be watching an area of storms develop. As they do, they may form into a bit of a cluster and move into Illinois later into the evening. By 1-2 AM Thursday the area of rain and storms is forecast to be entering western Illinois across zone 7.
Through the overnight this cluster of storms or MCS (Mesoscale Convective System) will continue across Central Illinois along the cold front.
By Thursday morning the NAM does show this system weakening as it heads east.
With 3000 J/Kg of CAPE leftover from daytime heating and a strong 850 mb jet of 40-50 mph. I do think this cluster of storms will be capable of strong to severe storms overnight Wednesday. Damaging winds, hail, and an isolated tornado would be the main threats.
New rainfall totals across the area do look rather impressive with an average of .50-1” across Illinois. However, places that do get under the strong to severe storms could see 2.5-.3.5” of new rainfall through late Wednesday night.
THURSDAY – FRIDAY: Through the early morning hours on Thursday the cold front to the west will move across the region. While rain and some storms will be possible as the front moves through early in the day, rain chances looks to end across most of the area by mid-day.
However, some models are a bit slower than others with the exact exit time of rain chances Thursday morning. We will fine-tune that as we get closer to the forecast period.
Highs on Thursday will be in the low to upper 70’s.
Through most of the day on Friday an area of high pressure will ridge in and will gain control of our weather. This will allow sunny to mostly sunny skies to persist through the day.
By late in the evening into the overnight Friday a back door cold front will swing through the forecast area. As it does, isolated to scattered areas of rain will develop and move through overnight. However, it’s not looking like any serious rain will come from this disturbance.