textproduct: Central Illinois

KEY MESSAGES

- Beneficial rainfall chances continue this week. Through Thursday morning, the best chance for additional rainfall over 2" is near and south of a Shelbyville to Paris line (60-70% chance). Rainfall amounts are expected to be lighter (less than 0.5") near and north of the I-74 corridor.

- There is a Marginal Risk (level 1 of 5) for severe storms southwest of Jacksonville tonight and south of the I-70 corridor on Wednesday. The main concern is large hail, but isolated strong winds could also occur. There could be another chance for severe storms late Friday.

- A warming trend is expected this week, with temperatures reaching the mid 70s by Friday.

UPDATE

Issued at 754 PM CST Tue Mar 3 2026

Made some minor grid updates based on radar trends. Main band of rain with embedded storms has laid out west-east along a zone of 850-700mb frontogenesis. This is being fed from the southwest, with MUCAPEs in excess of 500 J/kg, and PWATs around 1.25". Had a few reports of near/marginally severe hail late this afternoon, though mid level lapse rates have relaxed some in the past couple hours and updrafts have correspondingly weakened. But, given the instability small hail is possible in any stronger storms this evening. The band of better forcing will gradually shift south with time and weaken with much of the precip shown dissipating by CAMs around 2-4 AM. Radar estimates show in localized bands 1-2" has already fallen, heaviest from southern Macon to southwest Douglas counties. Additional QPF tonight should be in the 0.25-1.25" range for the central and southern CWA. Given the antecedent dry conditions do not expect hydo issues, unless localized training of stronger cells develops where heavy rain has already fallen today.

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DISCUSSION

Issued at 145 PM CST Tue Mar 3 2026

*** THROUGH EARLY WED ***

A warm front was draped over southeast IL (between the I-70 and US- 50 corridors) into portions of cntrl and SW MO as of 12pm/18z. As expected, temps north of the front have struggled to warm above the low 40s. With the exception of a few corridors across eastern IL, shower activity has waned considerably compared to this morning. MRMS rainfall estimates suggest a broad 0.50-0.75" of rain fell south of I-72 this morning, with a narrow stripe of over 1" just south of I-70. However, comparing to sfc obs suggests these estimates are overdone, with the measured values being more like 2/3 of the MRMS amount.

Zooming out, the slowly approaching upper trough was positioned over CO today, while an expansive sfc high over the Atlantic is helping advect Gulf moisture northward towards our stalled frontal boundary. Into this evening/tonight, continued WAA will lead to an intensifying warm nose around 800mb, above which elevated instability increases. The highest MUCAPE is expected across SW portions of the ILX CWA, with up to 1000 J/kg. Effective shear for parcels lifted from this level is around 30-40 kts, and these conditions are conducive for hail with the strongest updrafts. A marginal risk (level 1 of 5) was introduced for areas near and southwest of Jacksonville, but some sub-severe hail wouldn't be a surprise further northeast.

CAMs suggest showers and embedded storms will increase in coverage after about 5-6pm/23-00z, with continued activity focused within an east-west oriented corridor through the night. There is some minor variation in the exact placement of this activity, but most CAMs suggest it will be somewhere near or in between the I-72 and I-70 corridors. Through midday Wednesday, localized rainfall amounts within this corridor could approach 3 inches. Given the ongoing drought and lack of a frost depth, it seems unlikely that any hydrologic issues arise even with 3" of rain in a 24 hour period. CAMs also depict a rather tight northern gradient, such that areas north of a Macomb to Rantoul line may largely miss out on this overnight activity. The probability of exceeding a half inch of rain between 18z today and 18z Wed drops from 60% in Lincoln to less than 20% north of that Macomb to Rantoul line. Fog development remains possible tonight, especially near/south of I-72, but there was not a strong signal for dense fog.

*** WED - THUR ***

The upper trough continues its approach, nearing the area by Wed evening and resulting in a weak sfc low moving up the frontal zone and tugging the frontal zone northward. After a relative lull in precip Wed morning, rain chances ramp back up during the afternoon and especially into the evening/overnight. There is once again a low- end hail threat, with the best environment existing south of I-70 during the evening/overnight (MUCAPEs approaching 1000-1500 J/kg). There is a marginal risk of severe storms in that area. With low- level convergence near the front/sfc low, synoptic lift, and saturated low-levels, fog is once again a concern, especially given earlier rounds of rain. Some dense fog is possible Wed night.

Precip chances may linger into Thurs morning across the eastern half of the forecast area, but rain should come to an end as the upper trough departs and height rises occur aloft. Highs are expected to reach the 60s on Thurs.

*** FRI - SAT ***

The upper pattern remains highly amplified late in the week, characterized by a deep trough emerging onto the western Plains and a ridge axis over the eastern US. Lee cyclogenesis will result in a warm front lifting north across the ILX CWA, with strong southerly wind fields across the warm sector. These winds will advect additional Gulf moisture northward, with PWATs over 1" and sfc dewpoints approaching 60F. Some scattered storm development is possible Fri AM in the vicinity of the warm front as it lifts northward, otherwise, much of the open warm sector appears capped during the day. High temps are forecast to reach the mid-70s, which is generally below records but not far off in a few locations.

Strong SW flow continues into the night, keeping anomalously warm (potentially record warm) nocturnal temps in place beneath a strengthening LLJ (850mb flow increasing over 50 kts). A cold front and ongoing storms are expected to impinge upon this warm moist airmass across IL Fri night. The Storm Prediction Center has areas from St. Louis to Kankakee and westward in a Slight Risk (15-29% chance) of severe storms Fri night, although the risk is definitely greater further to the west where the diurnal timing is more favorable. To what extent instability, particularly sfc- based instability, persists across the ILX CWA will go a long way towards determining the severe potential Fri night. One other factor to note is the sfc low will be tracking across IA into northern portions of WI, which is quite aways removed from the local area. Thus, the sfc winds across IL are unlikely to back, resulting in relatively unidirectional profiles in the low-levels. Still, with sfc-1k shear in excess of 30 kts, a tornado threat could develop if sfc-based instability persists.

Additional storm development is possible along/ahead of this front on Sat, but whether or not that occurs across E/SE IL or if the front has pushed south of our area remains to be determined.

Erwin

AVIATION

(For the 00z TAFs through 00z Wednesday Evening) Issued at 525 PM CST Tue Mar 3 2026

IFR ceilings will be common for the central IL terminals through Wed afternoon. The exception in KPIA, where ceilings are MVFR currently. Here, IFR ceilings are forecast to work back north around 12z and then persist through 00z. Repeated rounds of scattered TSRA will be around this evening, especially at KSPI- KDEC- KCMI. Current guidance shows a break in the more widespread activity later tonight through Wednesday morning, before another round of TSRA develops during the afternoon. Handled that with a PROB30 group due to timing and coverage concerns.

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ILX WATCHES/WARNINGS/ADVISORIES

None.