Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
247 FXUS63 KILX 201735 AFDILX Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 1235 PM CDT Fri Sep 20 2024 .KEY MESSAGES... - There is a marginal risk (5-15% chance) for severe weather east of the I-55 corridor between 2pm and 8pm today. Primary threats will be damaging wind gusts and large hail. - Greater rain chances materialize Saturday night through Monday. There is a 50-60% chance of 1-2 inches of rain across central Illinois during that time period. && .UPDATE... Issued at 1058 AM CDT Fri Sep 20 2024 15z/10am surface analysis shows a weak cold front along the Illinois River...with the band of showers/storms that impacted parts of the area early this morning now completely dissipated across western Indiana. Sunny skies currently prevail across the KILX CWA: however, models continue to indicate widely scattered thunderstorm development along/ahead of the advancing front this afternoon. HRRR has been consistently keeping things dry until about 5-6pm when a few storms form along a Champaign to Taylorville line. With dewpoints hovering in the upper 60s to around 70 degrees, SBCAPEs are progged to exceed 2000J/kg by peak heating. Despite favorable instability, mitigating factors for widespread storms will be weak convergence along the boundary and strongest deep-layer shear lagging well to the W/NW of the instability axis. Nevertheless, a few strong storms with isolated damaging wind gusts and hail will be possible this afternoon and evening...focused east of I-55 between 2pm and 8pm. High temperatures will range from the upper 80s in the Illinois River Valley to around 90 degrees elsewhere. Barnes && .DISCUSSION... Issued at 345 AM CDT Fri Sep 20 2024 Early morning surface map shows a cold front from western WI into far eastern Iowa and nw MO. Isolated showers had recently develop nw of Lincoln while more widespread showers and a few thunderstorms were over southeast WI and northern IL, mainly north of I-88 and supported by a 25-30 kt sw 850 mb jet. Variable sky cover over CWA, with less clouds in eastcentral and southeast IL and more clouds over western/sw CWA. Temps ranged from 58F in Danville to 75 in Springfield, while more moist dewpoints were in the low to mid 60s, except mid to upper 50s from Rantoul to Terre Haute east. Aloft a strong 592 dm 500 mb high was over central Texas and ridging ne into IL and the central and eastern Great Lakes. A strong 553 dm 500 mb low was over east central Manitoba with a 567 dm 500 mb low off the southern CA coast. Latest CAMs push cold front se across the IL river valley late this morning and thru rest of central IL during this afternoon before stalling in southeast IL this evening. Isolated to scattered showers and isolated thunderstorms possible into mid morning over central IL, then a lull late morning and mid day, before more isolated to scattered convection develops along and ahead of se moving cold front in east central IL during mid/late afternoon and moving into southeast IL during this evening. SPC day1 outlook continues marginal risk of severe storms from Kankakee to Decatur to Taylorville and East St Louis east from mid afternoon (after 19Z/2 pm) into mid evening. There is 5% risk of damaging winds and large hail. Wind shear is 30-35 kts in east central IL and 25-30 kts in southeast IL, while MLCAPEs peak at 1-2k j/kg by late afternoon. Upper level ridging over IL keeps low lapse rates and limiting factor for more widespread strong to severe storms. Much of area should be dry overnight into Saturday with slight chances of convection Saturday afternoon west of Springfield and Peoria as warm front lifts back north/ne over central IL on Saturday. Very warm and rather humid conditions prevail today and Saturday with highs in the upper 80s to around 90F, with afternoon heat indicies in the low to mid 90s today and upper 80s and lower 90s Sat (mid 90s southeast of I-70 Saturday afternoon). A stronger cold front to move se into nw IL by dawn Sunday and more widespread convection to spread over central IL during overnight Sat night into Sunday morning. Fairly high chances of showers and thunderstorms expected to continue Sunday through Monday night with frontal boundary over central IL and moving into southeast IL Monday night. Rainfall amounts from overnight Sat night through Monday of 1-2 inches likely with locally high amounts nw of I-70 possible. Cooler highs Sunday in the mid to upper 70s in central IL and lower 80s in southeast IL. A few degrees cooler Monday with highs in the lower to mid 70s in central IL and around 80F in southeast IL. Larger model spread during middle and later part of next week and stayed close to model blend with generally dry conditions Tue thru Friday and highs in the 70s with lows in the low to mid 50s Tue night thru Thu night. 07 && .AVIATION... (For the 18z TAFs through 18z Saturday Afternoon) Issued at 1226 PM CDT Fri Sep 20 2024 VFR conditions will prevail through the entire 18z TAF period. Latest observational data shows a weak cold front approaching I-55: however, due to synoptic subsidence in the wake of the showers from earlier this morning, no diurnal cloud cover has yet developed. CAMs have been consistently featuring widely scattered convection after 5pm/22z primarily along or just south of a KCMI to KDEC line. Given trends, have opted to only mention VCSH at KCMI/KDEC between 23z and 02z. After that, any convection that forms will drop well south of the terminals and dissipate. Once the cold front passes, light/variable winds are expected tonight followed by SE winds of 5-10kt by Saturday morning. Barnes && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$