


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
344 FXUS63 KILX 111949 CCA AFDILX Area Forecast Discussion National Weather Service Lincoln IL 215 PM CDT Fri Jul 11 2025 .KEY MESSAGES... - Enhanced risk (level 3 of 5) for severe weather this evening in areas near and north of the Illinois River Valley. Damaging winds, hail, a tornado or two, and heavy rainfall are forecast. Timing is from 6pm to 11pm. - Daily chances for afternoon/evening thunderstorms will be seen through the weekend. SPC has a marginal risk for severe weather in place for Saturday and Sunday. - Hot and humid conditions will be in place through the end of this week and again early next week. Temperatures look to trend cooler by the end of next week. && .DISCUSSION...(through next Thursday night) Issued at 208 PM CDT Fri Jul 11 2025 A seasonably hot and humid airmass will remain in place through the weekend as a parade of shortwave troughs push across the Mid- Mississippi Valley. The net effect will be daily chances for thunderstorms, some of which may carry an attendant risk for severe weather and/or flash flooding. This afternoon, very buoyant boundary layer conditions have evolved across the warm sector, with central and southeast Illinois positioned south of a sharpening warm front. Sfc temps have warmed into the upper 80s with dewpoints in the mid 70s. The latest 18z RAP analysis suggests no residual capping exists amid a backdrop of moderate MLCAPE (1500-3000 J/kg), with the greatest of this instability focused across far west central Illinois. Within the kinematic parameter space, an area of enhanced deep-layer shear (30-40 kts) is being analyzed near and north of the I-80 corridor over eastern Iowa and northern Illinois, and is directly tied to a narrow mid-level speed max lifting across that area. A quick glance at water vapor imagery reveals a few subtle shortwave impulses lifting northeastward over north-central Missouri and south-central Iowa, ahead of both a stronger convectively-induced shortwave and the main shortwave trough axis. These more subtle shortwaves could provide the necessary forcing to support scattered thunderstorm development as early as this afternoon across west-central Illinois, mainly between 4-6pm local time. Short but cyclonically curved hodographs this afternoon support skinny, cellular updrafts that may have a tendency to consolidate and grow upscale fairly quickly. Mesoscale soundings from the HRRR in areas north of the Illinois River valley reveal very steep low- level lapse rates (> 9.5 C/km) and robust DCAPE values (> 1100 J/kg). This all adds up to a large hail (up to quarter size) and damaging downburst (greater than 60 mph) risk with any storm that may develop this afternoon. The greater chance and better coverage of thunderstorms will come this evening (between 7-10pm local time) with the arrival of the stronger, convectively-induced shortwave. This disturbance will once again augment deep-layer shear (30-40 kts) across portions of southeast Iowa and west-central Illinois. In addition, a modest low-level jet will begin to veer into west central Illinois, helping to maintain a favorably buoyant parameter space. The hodograph, while it does lengthen a bit due to the impinging LLJ, is not supportive of isolated supercells, especially with the mean wind and deep-layer shear vectors discouraging cross-boundary flow. Instead, new updrafts will have a tendency to consolidate and become linear. This again supports primarily a damaging wind threat (gusts > 60 mph) across portions of west central and central Illinois. Modest low-level ambient shear and strong theta-e differentials suggest the line of storms may quickly become outflow dominant as they evolve eastward in time and space later this evening. This lends a question as to how far east the damaging wind threat may extend, with the greatest risk perhaps staying west of I-55. Once the line of storms becomes outflow dominant later this evening, the risk for heavy rainfall and flash flooding could still remain overnight as the mature cold pool and modest LLJ work together to help maintain updraft development beneath a sink of healthy MUCAPE. Rainfall rates could eclipse 1/hr wherever backbuilding occurs. But overall, the coverage of storms should continue to fade overnight as the convectively-induced shortwave departs our area. Additional storm development is likely Saturday afternoon as the synoptic cold front pushes in from the west. A favorably buoyant environment will once again evolve by around midday, though deep- layer shear will be notably less present tomorrow (< 20 kts). The relatively weak deep-layer shear and poor mid-level lapse rates (< 6.5 C/km) suggests updrafts will struggle to hold together. Thus, both coverage and intensity of thunderstorms tomorrow ought to be less than today. Still, there will be enough sfc convergence along the front to support at least scattered storms. As we head into next week, some uncertainty remains with how far south the cold front will drift before washing out on Sunday. Right now, our southernmost counties remain clipped by a marginal risk by SPC. Elsewhere across our area, conditions appear to become drier and continued seasonably hot through at least Monday as a ridge builds in. Rain chances then increase by the middle-to- late stages of next week as shortwave activity increases across the Plains and helps push a few sfc boundaries across central IL. MJA && .AVIATION... (For the 18z TAFs through 18z Saturday Afternoon) Issued at 1248 PM CDT Fri Jul 11 2025 Primary aviation forecast challenge will be timing the convection later today. 1730z/1230pm visible satellite imagery shows very little Cu across central Illinois...suggesting weak subsidence along/north of an old outflow boundary. As this boundary dissipates and/or mixes northward, SCT-BKN Cu at 3500-4000ft will blossom across central Illinois this afternoon. Widely scattered showers/storms will be possible as well, but areal coverage will not be great enough to mention in the TAF at this time. Will monitor radar trends and add thunder if appropriate as the afternoon progresses. Further west, a line of thunderstorms is expected to develop along a cold front this afternoon...then push eastward into central Illinois during the evening. While CAMs still exhibit some minor timing differences, general consensus suggests the line will reach KPIA between 01z and 04z...and further east to the I-55 corridor in a weakening trend between 03z and 06z. Have included TEMPO groups for thunder at KPIA/KBMI/KSPI accordingly. Models indicate a further weakening of the convective line further east, so PROB30s still seem adequate for KDEC/KCMI overnight. Once the line passes, NAM/HRRR both suggest a period of MVFR ceilings developing along/west of I-55 by early Saturday morning. Barnes && .ILX WATCHES/WARNINGS/ADVISORIES... Flood Watch until 1 AM CDT Saturday for ILZ027-028-030. && $$