AFTERNOON-OVERNIGHT: Energy from the trough across the desert southwest and the positive tilted trough in place across the Great Lakes regions will provide the energy for rainfall over the next day or so. Currently rain is moving into southwestern/southern Illinois. However, thanks to dry air in place at the surface, it is evaporating before it hits the ground in places.
Through the day rain will continue to try to move into Illinois from the west and southwest. However, with the dry air in place, the air will have a hard time becoming saturated across zones 6 and 7. So while some showers will occur earlier today, I believe the heavier precipitation will hold off until later.
Through the evening the atmosphere should have more moisture in it. This will allow rain coverage to begin to increase from west to east across Illinois around 6-7 PM this evening.
Through the evening into the overnight, heavier, more persistent rain will move into the forecast area. By 12-1 AM the heavier rain will be located across the I-70 corridor and just south of it.
Through the overnight precipitation will continue to stream into zones 6 and 7. By 5 AM rain will still be occurring across the forecast area, especially across zone 6, some of this will be heavy at times. While I won’t rule out some a stray t’storm I do think very low to no instability will hinder thunderstorm formation.
Lows overnight will be in the mid 40’s north to low 50’s south.
TUESDAY: Rain will be ongoing across Illinois at 7-8 AM, with more scattered chances across most of zone 7 and better chances across southern zone 7 and zone 6. Some rainfall will be moderate to heavy at this time.
An area of high pressure will begin to ridge its way in from the north through the morning hours Tuesday. As it does, it will do a couple of things, the first is drier air will work in so rain will start to evaporate once again.
The second is, it will push the rain south. By 12-1 PM only isolated to very widely scattered areas of rain will be left across zone 7 and most of zone 6. This with scattered rain possible across southern zone 6.
Rain chances will remain across zone 6 through the evening, by 4-5 PM some scattered area of rain will remain possible.
Highs on Tuesday will be in the low to upper 50’s.
Through the evening rain will continue to come to an end across zone 6 and 7. By 10 PM only a few showers will remain possible.
New rainfall totals look to be heaviest around the I-70 corridor and just south. Models are in very good agreement with placement and amounts. A large swath of .50-1” looks likely across southern zone 7 and zone 6. Then heavier amounts will be embedded in that swath where the heavier, more persistent banding occurs. In Those areas, new rainfall totals of 1.75-2.25’ will be possible.
Through the overnight Tuesday, the area of high pressure will move in and drier air will overspread the forecast zones. This will give way to mostly clear skies with only a few clouds left in place.
Lows overnight will be in the low 40’s to near 50.
WEDNESDAY: The area of high pressure to the northwest will remain in control of the weather on Wednesday. This will allow sunny to mostly sunny skies to continue in many places.
There is a weak disturbance moving through at 500 mb on Wednesday. While this may be enough to allow some afternoon clouds to develop, a dry day is expected across the forecast zones.
Highs on Wednesday will be in the low to mid 60’s.
THURSDAY-FRIDAY: The area of high pressure will start to move off the east. However, it will still have the largest impact on the weather across the forecast region.
While an area of low pressure will be moving closer to the region from the southwest on Thursday, the area of high pressure will slow it down some. This will allow conditions to remain dry with mostly to partly sunny skies.
Highs on Thursday will warmer with temperatures topping out in the mid 60’s to low 70’s.
Thursday night the area of high pressure will move out of the forecast area and the area of low pressure will start to move in. As the low moves in, rain chances will be on the increase through the overnight into Friday.
Through the day on Friday the area of low pressure looks to move right along the Ohio River, this track would bring in more chances of rain and possibly some t’storms through the day on Friday.
WEEKEND: The weekend does look unsettled and cool. This will be thanks to an upper-level low that gets cut-off temporarily from the main flow. This will spin across the region both Saturday and Sunday.
With that in place, at least isolated to scattered rain chances will be possible both days. While models are not totally in agreement with timing/location of the low and precipitation chances, it’s forecast we will be fine-tuning in the future.
7 DAY FORECAST ( TEMPERATURES WILL VARY USUALLY WARMER SOUTH TO COOLER NORTH)