AFTERNOON-OVERNIGHT: A stationary front remains to the north of the region this morning with a warm front sitting the south of the zone forecast area. However, we are watching a line of storms that developed to the west and are moving into the Illinois. Some of these have prompted some severe t’storm warnings as they move eastward.
Through the morning into the afternoon the area of storms will continue eastward across Illinois, these are associated with an area of strong 500 mb vorticy. As they move eastward this area of storms should continue as a line or possibly as a cluster. By 12- 1 PM the wrf model shows the cluster of storms.
With a surface boundary in place across the region this afternoon/evening some scattered rain and storms will remain possible across zones 6 and 7. By 5-6 PM the models do show some of those scattered areas of rain and storms.
Isolated to scattered rain and storms will persist through the evening across zones 6 and 7. However, as we get later in the evening we will lose instability and upper level support. So by 12-1 AM storms should really be winding down and coming to an end across the zones.
The threat for strong and severe storms is present today. Especially across zone 6 where the line to the west is forecast to impact. As mentioned before, it is associated with a strong area of 500 mb vorticity.
Winds aloft today are sufficient for severe thunderstorm development. 500 mb winds of 55-65 mph and 850 mb winds of 30-40 mph should prove enough to support a sustained severe weather threat this afternoon and into the evening.
Clearing is already occurring in places ahead of the developing line west. This should allow at least some instability to occur. Models do suggest values of 2000-3000 J/Kg of CAPE could occur from I-70 southward.
These several factors do look to contribute to a severe weather threat this afternoon and evening. Again, the best chances of severe weather will be across southern Illinois where the line of storms to the west will move through. However, other scattered storms will be capable of reaching strong/severe limits as well. Main risks will be damaging winds and hail. However, an isolated tornado or two can’t be ruled out.
Heavy rainfall will also be a possibility though late tonight. It looks like .30-.60” will end up being the average rainfall across zone 6 and 7. However, places that do get under some of the heavier t’storms could see much more. Localized areas of 2-3” of rain over the next 24 hours will be possible, so some flash flooding could be a concern.
Through the overnight conditions will be dry and quiet across most of Illinois. The only exception may be across very southern zone 6. With a front in place just south of there, it could generate some storms overnight in that area.
Lows overnight will be in the upper 50’s to mid 60’s.
WEDNESDAY: With a low to the west on Wednesday conditions will start mostly calm and dry across the forecast zones. With perhaps a few showers and a couple of storms across southern zone 6.
Through the day it does appear sunshine will get through. This will allow the atmosphere to warm and once again become unstable through the afternoon. CAPE values as high as 4000-5000 J/Kg are forecast across southern Illinois via the NAM model Wednesday afternoon/evening.
Highs on Wednesday will be in the upper 70’s to mid 80’s.
Through the afternoon we will be watching a little area of vorticity move closer to the region. This may even be enough to create a small area of low pressure at the surface called a MCV or Mesoscale Convective Vortex. As this moves east into an unstable environment t’storms will start to develop along and around it.
By 4-5 PM thunderstorms look to get going across western Illinois as this moves through.
Through the evening this will continue its eastward movement across Illinois. While I will not be shocked to see some severe weather reports with this, I think the overall severe potential may be limited because of weak upper-level winds.
Wednesday evening into Thursday a cold front will be progressing into the forecast zones from the east. By 10-11 PM a line of rain and storms looks to be entering western Illinois. Some of these storm may be strong to severe at this time.
Through the overnight the front and storms will continue off to the east. As the do, the storms will likely be weakening. So while some strong to severe storms may be possible initially across western portions of zones 6 and 7, most storms will be fading as they head east. By 1-2 AM Thursday the NAM 4km shows the fading trend.
Lows overnight Wednesday into Thursday will be in the 60’s.
THURSDAY: Thursday morning some rain showers may be ongoing along the cold front. However, overall it does look to be mostly dry by 7-8 AM.
Through the day on Thursday the front will push to the east of the zone forecast area. Sunshine may even get in later on in the day.
Highs will be in the low 70’s north to upper 70’s south.
I do want to add, while most of the models are in good agreement that the front passes early in the day Thursday, the NAM is slower with the front. If this were to verify better rain and storms chances would be possible Thursday. It’s something we will watch closely for any changes or trends.
FRIDAY: An area of high pressure will ridge in on Friday. This will give us a very nice end to the week with sunny skies and dry conditions.
Highs on Friday will be in the upper 60’s north to mid 70’s south.
WEEKEND: Friday night into early Saturday a back door front will move through the region. As it does, the chance for some rain showers will increase across the area. Right now these don’t look heavy or real widespread, but the chance for those showers will exist.
Through the morning hours the front will move through and the showers will exit the region. By afternoon many places will be dry and precipitation free.
Highs will be cool with temperatures in the mid 50’s north to near 70 far south.
On Sunday an area of high pressure will be in control. Models are a bit unresolved on the forecast Sunday with some calling for afternoon rain, while others keep it to the south. If high pressure does build in as forecast, then I would lean more towards a dry day for most of the forecast area. However, it’s a forecast we will fine tune as we get closer to the forecast period.
7 DAY FORECAST (TEMPERATURES WILL VARY, GENERALLY COOLER NORTH/WARMER SOUTH)