AFTERNOON – OVERNIGHT: The upper-level ridge that has been in place over the past several days will break down over the next 12-24 hours. This will allow for more clouds and rain chances to enter the forecast across zones 6 and 7.
Through the afternoon and evening today the ridge aloft and an area of surface high pressure will remain in place. This will give us one last afternoon of rain free weather before better rain chances come in by Tuesday. However, to the west the large upper-level low will likely help clouds increase from west to east through the daytime hours.
While the daytime hours will remain dry across zones 6 and 7, rain chances will start to increase across the region overnight as the upper-level low moves closer to the forecast region.
By 2-3 AM tonight some scattered rain showers will be starting to enter western portions of the forecast zones. While most of these will be lighter in intensity, a few could produce some quick bursts of rain.
By 6-7 AM Tuesday morning scattered areas of rain and perhaps a few t’storms will continue to move to the northeast across zones 6 and 7. Again, some of these could produce some heavier times of rain along with some thunder.
Lows overnight will be in the low 50’s east to near 60 west.
TUESDAY: Scattered areas of rain and some t’storms will remain possible Tuesday morning through the mid-day hours.
The upper-level low will continue to push closer to the region through the afternoon hours on Tuesday as the high breaks down. As the low moves in, disturbances moving through the environment aloft will help generate more scattered afternoon rain showers and t’storms.
By 1-4 pm Tuesday afternoon the NAM 4km is a bit aggressive with rain coverage across the forecast zones. I think this may be over played in coverage across the area, with only scattered areas of rain and some t’storms.
Highs on Tuesday will be in the upper 60’s to mid 70’s across the forecast area. Winds could be a little breezy at times as winds gusts up to 20 mph or so from the east/southeast possible.
Tuesday night into Wednesday rain and storm chances will go down with more isolated to widely scattered precipitation chances overnight. Perhaps better rain/storm chances could be in place just north of the zone 7 area, so we will watch to see if there could be any southward shift in the placement of that rainfall.
Lows Tuesday night into Wednesday will be in the mid to upper 50’s.
WEDNESDAY: A surface area of low pressure will start to move towards the region from the west and southwest on Wednesday. As the low approaches Wednesday morning a warm front will start to lift north across the region. This will be the focal point for more rain/thunderstorm activity by 7-8 AM.
Through the morning the warm front will lift northward across Illinois. As it does more rain and t’storms will develop across zones 6 and 7 by 10-11 AM.
The surface area of low pressure will lift northward through the afternoon on Wednesday taking the warm front with it. While we are in the warm sector of the storm system rain and storm chances may be very isolated Wednesday afternoon between the cold and warm front.
By 6-7 PM the cold front will be pushing across Illinois. Rain and storms will develop along the front as the it pushes to the east Wednesday evening.
Looking at the latest forecast data I am not going to rule out some strong storms Wednesday evening. Wind aloft will not be all that impressive. However, IF some afternoon clearing could occur and instability could build in the environment, some strong storms would not be out of the question. There are still many details to be worked out over the next 24-48 hours regarding the strong storm chances.
Highs on Wednesday will be in the mid 60’s to low 70’s. Winds will be out of the south to southeast with gusts of 25-30 mph possible.
The cold front and associated rain/storms will move to the east across zones 6 and 7 Wednesday evening into the early overnight. By 10 PM-12 AM the front and precipitation look to be exiting into Indiana.
Lows Wednesday night into Thursday will be around 50 north to the upper 50’s south.
New rainfall totals through Thursday morning may be pretty healthy in some places across western Illinois. The latest model data would suggest 1-1.5″ of new rainfall would be possibly across western Illinois. While .40-.65 would be more common across eastern Illinois.
THURSDAY – FRIDAY: As the area of low pressure moves to the north of the forecast area Wednesday night and Thursday, a secondary cold front looks to move across Illinois with it. With the front in the area, rain and perhaps a few storms will remain possible across the region on Thursday.
I will be interested, but not shocked, to see the models speed up the secondary front. Bringing the front through late Wednesday night through early Thursday. However, we will watch it closely because it will have a large impact on the weather.
Highs on Thursday will be mid to upper 60’s.
Thursday evening though Friday models do show an upper-level trough moving through the forecast area. This would allow for unsettled weather to continue while the trough is in place.
Timing is a bit different in the long-range within the models. The CMC/EURO are slower with the overall progression of the upper-level trough keeping it in the region through mid to late Friday. Therefore, allowing rain chances to continue.
However, the GFS is a bit faster with the trough, exiting it to the east of the region earlier on Friday. With this solution rain would be out of the region and a dry end to the workweek would be expected.