textproduct: Central Illinois

KEY MESSAGES

- Severe storms are possible this afternoon into tonight. All hazards are possible, including tornadoes, some of which could be strong (EF2 or higher), large hail (2 inches or larger), damaging winds, and isolated flash flooding. There is an Enhanced Risk (level 3 of 5) of severe storms north of a Springfield to Danville line, with a Slight Risk (level 2 of 5) to the south.

- Record high temperatures are possible again today, with highs in the upper 70s to low 80s. It will also be seasonably humid, with dewpoints reaching the mid 60s.

- Total rainfall amounts through Wednesday could exceed an inch (40-70% chance). There is a low chance for localized amounts over 2 inches (10-20% chance).

UPDATE

Issued at 944 AM CDT Tue Mar 10 2026

Overall thinking is largely unchanged from the previous AFD regarding thermodynamic environment and synoptic scale features and forcing. One notable change, however, is some CAM guidance (particularly HRRR, RAP) shows a rapid erosion of the cap around midday. If the cap breaks early this afternoon, explosive convective development could occur this afternoon over the northern portions of the CWA. We'll be launching an 18z sounding to sample the environment ahead of initiation. Any afternoon storms would be capable of very large hail and damaging straight line winds given dry air and steep lapse rates in the mid levels. The tornado threat looks to be maximized over our far northern counties and points north, where curved hodographs are maximized closer to the warm front. Tornado risk does extend farther south into the central CWA, as low level flow enhances and backs slightly in response to surface low pressure tracking into SE IA by 00z. SPC's morning update did upgrade the tornado risk to "CIG2" showing a potential for EF3+ north of a Rushville to Bloomington line. Timing of severe risk extends well into this evening, when it will be augmented by a 40-50 kt 925 mb jet.

25

DISCUSSION

Issued at 244 AM CDT Tue Mar 10 2026

*** ENHANCED RISK OF SEVERE STORMS TUES PM ***

A volatile parameter space is expected to develop this afternoon into the late evening, supporting an all hazards severe storm risk. The new Storm Prediction Center Outlook did not change appreciably from the previous iteration. There is an Enhanced Risk (level 3 of 5) of severe storms northwest of a Springfield to Danville line, and a Slight Risk (level 2 of 5) to the south.

* Synopsis *

Early Tues AM, a cut off low that had been positioned west of Baja California has begun to slowly push east, and will continue to do so today. There is also a northern stream disturbance approaching the Plains. Together, these features will continue to produce pressure falls over the Plains, with two low pressure areas developing. One of these is over eastern CO, and is less relevant to our discussion, while the other is set to lift from central KS towards the Quad Cities over the course of the day. This approaching sfc low will track along a frontal zone, which as of 06z/1am Tues extended from far SE Nebraska to S Wisconsin.

Today, a tight warm front gradient is expected to develop across N IL, due in part to an enhanced lake breeze off Lake Michigan. High- res guidance has been consistent in showing this front positioned north of the ILX CWA this afternoon, likely closer to the I-80 corridor than the I-74 corridor. While the front is generally expected to be oriented east-west, it's exact orientation may be determined by the strength of the enhanced lake breeze. The orientation of the front will be relevant for whether or not storms that develop near it maintain sfc-based inflow or become elevated, which influences the associated hazards types. However, if the warm front is indeed north of our area as currently progged, the storms for which this is relevant would also be north of our area.

* Parameter Space *

All signs point towards central IL being in the warm sector through the day, with near-record warmth and unseasonably high dewpoints likely. Despite some cloud cover, temps will push into the mid 70s- low 80s, while dewpoints rise into the mid 60s. These conditions are more typical of a mid-May warm sector than early March.

There were no significant changes to the convective parameter space from previous forecasts. Seasonably high instability is expected, with the HREF mean depicting sfc-based CAPE over 2000 J/kg, and there will be ample deep layer shear to support updraft maintenance. Low-level helicity will be maximized near the warm front during the day, but increase across the warm sector into the evening, both in response to backing of sfc winds due to the approaching sfc low as well as the onset of a robust LLJ. The forecast 0-1km SRH values are over 150 J/kg, which is conditionally supportive of tornado development.

The degree to which sfc-based instability persists into the night will impact the storm hazards, as will the storm mode. At the very least, models depict moderate to high MUCAPE values persisting into the night, with strong wind shear from the impressive LLJ.

* Convective Evolution *

Forecast soundings continue to show strong capping through at least early to mid afternoon, with convective inhibition lingering across the warm sector into early evening. Latest CAMs depict development near or just south of the warm front mid- afternoon, although the area near the warm front is one of the more favorable areas for clouds this morning/early afternoon, which could mean CAMs are too quick to erode the cap. If these modeled storms did form around 2-3 PM, they would likely be supercells, and right-moving supercell motions favor a track parallel to the warm front. (That is, unless that lake breeze results in more of a NW-SE orientation of the warm front, which is a possibility and would favor more of a hail threat with these storms). At any rate, guidance suggests this threat is more likely just north of our forecast area, but it's close enough that we can't rule out being impacted by these potential storms (areas near/north of I-74 need to monitor).

Aside from the development near the warm front, additional storm initiation appears unlikely until the evening (6-8 PM) as the approaching sfc low and developing LLJ both increase ascent and help erode the cap. This development is most likely to occur near/NW of the IL River. Storm motions will be ENE, but the cold front gradually sagging south will push the storm chances southward during the late evening/overnight. Initially, all hazards appear possible, then deep layer shear oriented parallel to the front favors upscale growth, which would trend more towards a wind threat than a hail threat. The tornado threat will be modulated by whether or not sfc- based instability persists into the night, which remains a low confidence aspect of the forecast. It's a least plausible given sfc temps and dewpoints remaining in the 60s. The low-level wind profiles will be conditionally supportive of tornadoes, regardless of whether storms are semi- discrete or linear.

CAMs depict storms continuing near the frontal boundary into the overnight hours, with an uptick in coverage after about 2 AM, likely due to an MCV from convection over the southern Plains today and further aided by the approach of what was formerly the cut-off low near Baja California.

* Summary of the Severe Storm Threat *

All severe hazards are possible today, including strong tornadoes (EF2+) and large hail (over 2"). The best chance for afternoon storms is near a warm front, which is expected to be just north of our forecast area (near the I-80 corridor), but these storms could occur as far south as I-74. Storm chances increase this evening, with the most likely area for development being near and northwest of the Illinois River between 6-8 PM. Storm chances slowly shift south late evening into the overnight. Wind may pose more of a threat than hail overnight. A tornado threat may persist into the night. Localized flash flooding could occur due to training storms (10-20% chance of rainfall over 2").

*** WEDNESDAY ***

CAMs vary on the placement of the front into Wed AM, with some bringing it south of the ILX CWA and others keeping it across E and SE IL. If the front does linger long enough that sfc instability starts to increase ahead of it (mid to late morning), more severe storms could develop. The storm mode at that point would likely be linear, favoring wind damage and perhaps embedded tornadoes owing to continued strong low-level shear. For now, the CAMs that show a slower front are outliers, so the Day 2 SPC Outlook is focused south of our forecast area. We will continue to monitor, just in case things trend in an unfavorable direction. At any rate, precip may linger north of the front, gradually decreasing from NW to SE through the day. Expect non-diurnal temp trends on Wed, with temps falling during the day. Areas NW of I-55 will only reach the 40s, while areas to the SE go from the mid-50s to mid-60s in the AM to the 40s by late afternoon.

Total rainfall amounts from this mid-week system could wind up being a case of haves and have-nots, due to the scattered, convective nature of the precip. On the high-end, localized amounts of 2-2.5" are possible, per the HREF LPMM and NBM 90th percentile. On the low end, some areas could receive as little as 0.25" (NBM 10th percentile).

*** THURSDAY INTO NEXT WEEK ***

A sfc high settles over the southern Plains for Thurs, then slides east as the next system tracks across the northern US and introduces southerly flow locally. That system continues to look like it could produce some light showers near/north of the I-74 corridor Thurs evening/night, but should be unimpactful.

The pattern remains progressive, with a large system developing over the Plains this weekend, approaching the Midwest by Sunday. Expect breezy southerly flow ahead of this system (Sat night into Sun). Latest ensembles depict the sfc low tracking through or just north of the ILX CWA on Sun. Will need to monitor the track for potential influence on p-type. Current indications are that rain is favored initially, but a switch to wintry precip is possible with this system. Behind this system, strong CAA is forecast, bringing much colder air into the region. By Sun night (as well as Mon night), there is a 40-70% chance for lows below 20 degF (chances increase with northward extent).

Erwin

AVIATION

(For the 12z TAFs through 12z Wednesday Morning) Issued at 545 AM CDT Tue Mar 10 2026

Satellite shows areas of low clouds filling in across eastern IL and lifting northward in time. MVFR ceilings are possible at all terminals this morning, but are least likely at KSPI. Some IFR ceilings could occur in eastern IL (KDEC/KCMI). Breezy southerly flow develops today, but the main concern for the TAFs comes after 00z as scattered strong thunderstorms gradually move from northwest to southeast across the region. Based on latest model guidance, trended the arrival time of thunderstorms a bit later at each terminal. Will also need to monitor LLWS potential as a strong LLJ develops overnight, with 2 kft winds approaching 50 kts out of the southwest.

Erwin

CLIMATE

Issued at 1249 PM CDT Sun Mar 8 2026

Record high temperatures for Tuesday:

Location Tuesday ======== ========= Bloomington 78 (1893) Champaign 73 (1990) Charleston 79 (1990) Decatur 79 (1990) Lincoln 78 (1955) Olney 80 (1990) Peoria 77 (1955) Springfield 80 (1955)

Geelhart

ILX WATCHES/WARNINGS/ADVISORIES

None.