textproduct: Central Illinois

KEY MESSAGES

- Severe storms appear likely late Tuesday afternoon into Tuesday night. Storms will be capable of producing tornadoes, some of which could be strong, as well as large hail, damaging winds, and isolated flash flooding. There is an Enhanced Risk (Level 3 of 5) of severe storms northwest of a Springfield to Hoopeston line, with a Slight Risk (level 2 of 5) to the south.

- A warming trend continues through Tuesday, with well-above normal temperatures in the 70s today, then near 80 degrees on Tuesday. Some locations could set record high temperatures.

- Total rainfall amounts from the mid-week system are favored to exceed an inch (60-70% chance), and localized amounts over 2 inches are possible (20-30% chance).

DISCUSSION

Issued at 209 AM CDT Mon Mar 9 2026

*** THROUGH TONIGHT ***

Early Mon morning, a cut-off upper low remains positioned near Baja California, with quasi-zonal flow across the CONUS and a few shortwaves present over Canada. With a sfc low passing by to the north, breezy SW flow persists today, advecting both moisture and warmth northward. Highs are expected to push well above normal, in the mid 70s, while dewpoints rise into the low 50s by this afternoon (notably higher than the low 30s that occurred on Sunday). Locations near the I-74 corridor could approach record highs today. Refer to the Climate section of the AFD for a specific listing of existing records.

High-res guidance depicts diurnal Cu developing first across eastern IL by late morning, then expanding westward in time. This general evolution is supported by fcst soundings as well, showing deeper mixing required to reach LCLs across the western half of the CWA.

The continued southerly flow into tonight will keep lows mild, in the mid/upper 50s, which is well above the normal lows (near freezing). Can't rule out some advection fog development tonight, but guidance does not appear overly bullish at this point. Lingering cloud cover may help limit the fog potential. The latest HREF (09.00z) has the probability of visibility below 2 miles ranging anywhere from 10-40% across the region.

*** MID-WEEK SYSTEM ***

* Near-Record Warmth and Severe Storms Tuesday PM *

On Tues, the aforementioned cut-off low over the SW begins to emerge, along with a northern stream disturbance. These will lead to sfc pressure falls over the Plains, and latest high-res guidance indicates that by Tues afternoon a weak sfc low will be positioned over S IA with a warm front extending eastward. The exact latitudinal position of this warm front may still shift in subsequent model updates, but for now models place it somewhere between the I-80 corridor and the northern fringes of the ILX CWA (Galesburg to Pontiac). Across the warm sector, near-record highs remain possible as temps surge into the upper 70s/near 80. Gulf moisture also advects into the area, with dewpoints pushing at least into the low 60s, potentially higher.

A volatile parameter space is expected to develop, with seasonably high instability (approaching 2000 J/kg of SBCAPE), steep mid- level lapse rates, and favorable wind profiles (45-50 kts of bulk shear, exhibiting clear veering in the low levels). Scattered to numerous severe storms are possible. The parameter space could be further enhanced via backing of sfc winds in response to the sfc low northwest of the area, as well as in the vicinity of the warm front. 0-1 km storm-relative helicity (SRH) values are supportive of tornadoes within the entire warm sector (over 150 J/kg), but are especially so near the warm front (approaching or exceeding 300 J/kg). Deep layer shear vectors are close to parallel to the warm front across IL, and the bunkers motion for right- moving supercells is almost due easterly (also parallel to the front). This raises concern that a supercell could maintain a prolonged residence time near the warm front, which would carry a substantial tornado risk. Large hail (over 2") is also a concern given this parameter space and the initial discrete or semi- discrete storm mode. The Day 2 Convective Outlook maintains an Enhanced Risk (level 3 of 5) across the northern half of the ILX CWA, and a Slight Risk (level 2 of 5) to the south. Tornadoes and large hail are the top concerns, but all hazards are possible.

In terms of timing, the expectation remains that strong capping will limit convective development through the morning and early parts of the afternoon. CAMs tend to struggle at identifying when the cap will break, but the best estimate right now based on forecast soundings is that the potential for storm development increases quickly around/after 5 PM. That's not to say earlier development can't occur, but the chances certainly ramp up into evening. Used 3- hour PoPs in the gridded forecast Tues afternoon to highlight this evolution, with a 20-40% chance of storms north of I-72 between 1-4 PM, increasing to 40-60% chance between 4-7 PM.

Into Tues night, that aforementioned sfc low over IA is progged to slide east along the frontal zone towards Chicago, sending a cold front pushing slowly south into the ILX CWA Tues night. Combined with the onset of a robust LLJ, convective coverage is likely to increase overnight, with high PoPs across our forecast (80-90%). The orientation of the shear vectors relative to the cold front favors upscale growth, and forecast soundings show mid-level lapse rates becoming less steep during the night, suggesting storms transition to more of a wind threat rather than a hail threat. The diurnal timing is not favorable for tornadoes, but if any surface based instability can persist into the night, the robust LLJ will result in high 0-1 km storm-relative helicity.

Latest guidance still shows the front bisecting the ILX CWA Wed morning, with widespread precip ongoing. The front progresses SE in time and eventually exits by the afternoon. Can't rule out some strong to severe storms ahead of the front on Wed, as moderate wind shear persists. However, the mid- level lapse rates appear meager at best, resulting in substantially lower instability than Tues. Deep layer shear vectors remain parallel to the cold front, favoring continued upscale growth, so the main concern would be isolated strong wind gusts. Hodographs appear unidirectional in the low levels, and despite strong winds at 1 km AGL there is only 30 kts of 0-3 km shear, all of which is oriented parallel to the front. Typically, we seek 30 kts of 0-3 km line- normal (not line- parallel) shear for a QLCS tornado threat, so this analysis suggests the tornado threat is low during the day Wed. There is a Marginal Risk (level 1 of 5) of severe storms in far southeastern Illinois (Lawrence County) on Wednesday.

*** RAIN OUTLOOK ***

Precipitable water (PWAT) values are forecast to be between 1.2-1.5" across the warm sector, which is the near the maximum of the ILX observed sounding climatology. We're not quite to the point that CAMs can capture the entirety of this event, but the coarser ensemble guidance is still depicting a 60-70% chance of total rainfall over 1" and a 20-30% chance for over 2". There are some indications that back-building (or training) of storms is possible Tues night, as fcst soundings show a period where the cloud layer winds are similar (in both magnitude and orientation) to the LLJ winds. It would not be a surprise if future CAM runs depicted locally higher rainfall amounts approaching 3" in spots. There is a Slight Risk (level 2 of 4) of Excessive Rainfall, encompassing areas roughly from Sangamon to Vermilion Counties and northward.

*** REST OF THE WEEK ***

Following the cold frontal passage on Wed, temps cool towards seasonable values (near 50F) on Thurs, with high pressure sliding east into the area. A compact low pressure tracks into the Great Lakes by Fri AM, with the resultant pressure gradient producing breezy southerly flow Thurs night keeping lows above normal, near 40F. Some light, WAA-induced rain is possible Thurs night into Fri AM, but the precip associated with this system will largely be focused north of our forecast area. Another system remains on track to move across the Midwest during the latter half of the weekend.

Erwin

AVIATION

(For the 18z TAFs through 18z Tuesday Afternoon) Issued at 1235 PM CDT Mon Mar 9 2026

Stratus clouds with bases of 1-2k ft was drifting northward toward DEC airport at 1730Z and should lift into CMI during next hour or so. Ceilings/bases of stratus clouds slowly lifts during this afternoon but still MVFR ceilings likely at DEC and CMI and may get close to BMI airport late this afternoon. Latest HRRR keeps low stratus clouds east of I-55 this afternoon and evening. But more widespread low clouds to develop late tonight and linger into Tue morning, with bases as low as 500-1500 ft along with MVFR vsbys possible in light fog. A few of the CAM members like NAM 3km, HRRR and RRFS show isolated showers over central IL between 03-09Z tonight but coverage appears too isolated to mention in central IL TAFs at this point. Breezy SSW to SW winds around 15 kts with gusts around 25 kts this afternoon to weaken to 10-14 kts this evening (even lighter at PIA) and around 10 kts overnight into Tue morning.

07

CLIMATE

Issued at 1249 PM CDT Sun Mar 8 2026

Record high temperatures for Monday and Tuesday:

Location Monday Tuesday ======== ========= ========= Bloomington 73 (1974) 78 (1893) Champaign 73 (1925) 73 (1990) Charleston 79 (1925) 79 (1990) Decatur 78 (1925) 79 (1990) Lincoln 78 (2000) 78 (1955) Olney 81 (1925) 80 (1990) Peoria 71 (1918, 2021) 77 (1955) Springfield 75 (1918, 1925) 80 (1955)

Geelhart

ILX WATCHES/WARNINGS/ADVISORIES

None.