AFTERNOON-OVERNIGHT: Mostly to party clear skies have started off the day across zones 6 and 7, with a few showers entering southwestern Illinois near the St. Louis area. However, dry air is still in place this morning, so while moisture continues to try to steam in, it is evaporating keeping us dry with sunshine.
Through the morning into the early afternoon hours a few showers will be possible across southern zone 6 in Illinois. However, thanks to the dry air that remains in place, those showers will be very light in intensity. By 1-2 PM only a few showers will be ongoing.
Through the afternoon a MCV (Mesoscale Convective Vortex) will move to the southwest and south of the region. While the main area of storms will move to the south, this MCV will allow some storms to develop as the environment becomes more saturated. Scattered storms will be occurring closer to the MCV across zone 6 and possibly southern zone 7 at 5-6 PM this evening.
Through the evening into the overnight we will lose instability and the MCV will move away from the area. As this occurs, storms will move to the east losing steam as they do.
With CAPE values of 1000-1600 J/Kg in place this afternoon/evening some storms could be on the strong to low-end severe side with gusty winds, hail, and perhaps a brief spin-up. However, upper-level winds will be very weak, so widespread severe weather is not anticipated.
While most of the overnight looks to be dry, a few isolated to scattered areas of rain and a couple of storms may develop along a wind shift by 3-4 AM.
Lows tonight will be in the low 60’s north to mid 60’s south.
WEDNESDAY: By 7-8 AM Wednesday morning some isolated areas of rain and some t’storms will be developing across both zones 6 and 7 across Illinois. While many places will be dry, don’t be surprised if you get some early morning heavy rain and hear some thunder.
Throughout the day on Wednesday some upper-level pieces of energy will be moving through the upper-level flow. With such a warm, moist environment in place I can’t rule out rain/storm development as these move through. With that being said, scattered rain and t’storms will remain possible through the morning into the early afternoon on Wednesday across zones 6 and 7.
Through the afternoon on Wednesday there looks to be a break in activity across zones 6 and perhaps zone 7. If rain and storms can end over the forecast area through the afternoon on Wednesday some instability will build in. CAPE values of 1000-1500+ J/Kg will be possible tomorrow afternoon if we can destabilize the environment.
Through the late afternoon into the early evening another upper-level disturbance will move across the forecast zones through the potentially unstable atmosphere. As this moves east, rain and t’storms will develop along and ahead of the disturbance across zones 6 and 7.
Scattered rain and storms will continue across the forecast zones Wednesday evening. By 10-11 PM I do think scattered rain and storms will be weakening across the forecast area as the upper-level energy moves east and we lose daytime heating/instability.
Highs on Wednesday will be in the upper 70’s northwest to mid 80’s south.
While a few storms could be on the strong to low-end severe side Wednesday afternoon/evening, the overall threat will be limited. While instability and moisture may be decent, upper-level winds will once again be meager, therefore hindering the severe weather threat. If rain/storms do persist with more numerous coverage through Wednesday afternoon the overall strong/severe threat would be reduced even more. Main severe risks Wednesday will be damaging winds, hail, and perhaps a brief tornado.
Through the overnight Wednesday night into Thursday a few showers and an isolated t’storms will remain possible. However, I think most of the overnight will be quiet as we lose the instability needed to sustain thunderstorms.
Lows Wednesday night into Thursday will be in the mid 60’s to around 70.
THURSDAY: Late Wednesday night into early Thursday remains to be a complicated forecast as we will likely be watching a developing MCS develop outside of the forecast area. Right now most of the models develop this MCS across northern Illinois and move it southeast across the northern portions of Illinois and into Indiana.
However, the NAM 4km is much farther south bringing the complex of storms through southern Illinois. Then continuing the complex eastward through the morning hours Thursday.
While the more northerly solution would make sense to me, it’s a forecast we will fine-tune over the next 24 hours or so. Strong to severe storms do often accompany these complexes, so where it does track strong winds, hail, heavy rain, hail, and even an isolated tornado or two can’t be ruled out.
The forecast on Thursday afternoon will be highly dependent on the location/track of the MCS. Right now I think the cluster of storms will move to the east of most of the zone forecast area. If this occurs instability will build in through the afternoon. The NAM would support this idea with CAPE values of 4500-5200 J/Kg in locations.
This would be very high-end instability so afternoon t’storms would likely develop across zones 6 and 7, some of which could be strong to severe
Highs on Thursday will be in the upper 70’s to mid 80’s. Winds will be strong at times with gusts of 25-30 mph possible.
Thursday night into Friday conditions should begin to quiet down as we lose instability through the evening and overnight hours.
FRIDAY: Friday looks to start out dry across the forecast area. However, through the day a warm front will be making its way closer to the forecast zones.
As the front moves closer to the forecast zones rain and storms will develop late morning into the early afternoon along and ahead of the front. Rain and storm coverage may be pretty high Friday afternoon into the evening across zones 6 and 7.
While better upper-level dynamics will arrive to the region on Friday, the overall amount of rain and cloud cover may hinder instability. If rain and storms do persist through the morning and afternoon strong to severe storms would be unlikely.
Highs on Friday will be in the mid 70’s to low 80’s.
Average rainfall totals through the end of the week will be around .75-1.15” across the forecast zones. However, places that get under the storms or possibly the MCS could see locally more. The NAM 4 km shows pockets of 2.5-3.5” of new rainfall with local thunderstorms. However, totals of 3.5-4.5” where the MCS moves through!
WEEKEND: The warm front will lift northward through the region Friday through Friday night leaving us in the warm sector of the storm system for the weekend. While it will be very warm and humid this weekend, rain/storm chances will be lower. Right now only isolated to widely scattered afternoon pop up storms look possible both Saturday and Sunday.
Highs this weekend will be very warm with highs in the upper 70’s to mid 80’s Saturday.
Sunday even warmer air will spread in with highs in the low 80’s to possibly near 90 in locations!