textproduct: Central Illinois

KEY MESSAGES

- Widespread dense fog is expected east of the Illinois River this morning. Visibility should improve by mid-morning (around 9 AM).

- Multiple rounds of scattered storms are expected through Saturday morning, with the greatest coverage expected overnight (west of I- 57) into Saturday morning (east of I-57). Some of the storms could be strong to severe, especially late Friday afternoon into Friday night. There is a Slight Risk (level 2 of 5) of severe storms west of I-55, and a Marginal Risk (level 1 of 5) east of I-55.

- Unseasonably warm today, with highs reaching the mid 70s. Breezy southwest wind gusts of 30-35 mph are expected during the afternoon.

DISCUSSION

Issued at 212 AM CST Fri Mar 6 2026

*** SYNOPSIS ***

Deep troughing was evident over the Rockies at 1am/07z Fri, with clusters of t-storms ongoing from OK northeastward into IA. A developing sfc low was present in the lee of the Rockies, with sfc troughing extending well northward into the Dakotas. Closer to home, an east-west oriented warm front will lift north through the morning.

*** FRIDAY AM ***

Dense fog advisory remains on track at this time, with nearly all locations west of the IL River reporting vis below 1 mile as of 0630z/1230am Fri. There may be a need to expand the dense fog advisory to include areas west of the IL River. 06.00z HREF suggests a 40-50% chance for vis below 1/4 mile in these areas, albeit for a shorter period of time than areas to the east. Additionally, obs from KPIA show ceilings trending lower in time, now down to 200 feet from 800 feet just a few hours ago. Across the entire area, vis should improve rapidly between 14-15z (8-9 AM) as the front lifts north.

WAA and convergence along the leading edge of the nocturnal LLJ are expected to lead to scattered showers/storms lifting northeast across the CWA, primarily between 09-15z (3-9 AM). The better forcing is located west of our area, and thus the PoPs are highest west of the IL River (50-80%, compared to around 40% to the east). Recent regional radar imagery shows storms within this WAA/LLJ forcing weakening over the last half hour, so may need to lower PoPs soon if there aren't renewed signs of development. If any storms form this morning, they will be elevated (not surface based). As the low-level WAA strengthens the warm nose, elevated instability values could approach 1000 J/kg in spite of only modest mid-level lapse rates (less than 7 degC/km). These conditions could support a hail threat with these storms.

*** FRIDAY PM ***

The deep trough over the Rockies will break into two waves, the first lifting NE Fri PM and the other becoming a cut-off low near Baja California. The associated sfc low is expected to make its way across KS/IA into Fri night. Persistent southerly flow across the warm sector will advect unseasonable warmth and moisture into the ILX CWA. Despite partly to mostly cloudy skies, high temps are forecast to reach the mid 70s, which is 20-25 degF above normal. Dewpoints will also be unseasonable, with latest models suggesting values into the low/mid 60s which is an upward trend compared to the forecast from a few days ago. This has implications for the storm potential and timing.

Before discussing the storm threat, will also note that it will be breezy today as strong low-level wind fields develop in response to this amplified pattern. Forecast soundings show winds over 30 kts through much of the PBL. Even with the cloud cover, there should be sufficient mixing (or at least periods of mixing) that transport 30- 35 mph gusts to the sfc.

In prior forecasts, the storm evolution for today seemed fairly cut and dry: a chance for elevated t-storms with hail during the early AM, then strong capping limiting development area-wide through the PM until the cold front arrived overnight. However, the uptick in forecast low-level moisture makes the storm evolution less certain, owing to reduced capping. Some CAMs depict storm development near or NW of the IL River during the afternoon despite somewhat nebulous forcing. The potential culprits include outflow boundaries from convective activity this morning, as well as activity currently across OK/SW KS holding together as it tracks NE. If storms do form (or hold together), the parameter space should be supportive of severe storms, with seasonably moderate to high CAPE (1500-2000 J/kg), deep layer shear of 30 kts, and 0-1 km helicity (spin) over 100 J/kg. All hazards would be possible.

Additional broken lines of storms are expected to push in from the west during the late evening/overnight. CAMs appear somewhat disorganized with this activity, with HREF members depicting two broken, seemingly decaying lines of storms. Still, with MUCAPE values over 1000 J/kg and a strengthening LLJ, severe hail/wind threats will exist. There is uncertainty as to whether or not sfc- based instability is maintained into the night. Even if its not, it won't take much for showers/storms to mix strong LLJ gusts to the sfc. If sfc-based instability is maintained, LLJ forcing increasing over 50 kts could support embedded tornadoes. Aside from the instability, one potential limiting factor for the tornado threat is that 0-3 km shear vectors are expected to be roughly parallel to the convective lines, limiting the line-normal shear component. Still, a conditional strong tornado threat exists (2-5% chance of any tornadoes, reasonable maximum intensity of EF2).

In summary, multiple opportunities for severe storms exist over the next 24 hours, some of which are highly conditional. The latest SPC Outlook features a Slight Risk (level 2 of 5) west of I-55, with a Marginal Risk (level 1 of 5) to the east.

*** SATURDAY AND BEYOND ***

The cold front and associated convection are likely to be located near or east of the I-55 corridor around daybreak Sat, with a 60-80% chance of precip east of a Rantoul to Pana line. As diurnal heating increases instability ahead of the front, severe chances could also increase, but this may not occur until after this he front pushes southeast of the ILX CWA. Additionally, the upper low will be lifting further away, making the upper levels less conducive. Due to the progressive and scattered nature of these storm chances, QPF amounts appear unlikely to exceed 1" (this includes any storms on Friday).

Once this front moves through, the rest of the weekend appears dry. A weak sfc high pressure axis will be over the area Sat night, with lows expected to fall to the mid 30s. The sfc high shifts east to the TN Valley on Sun, reestablishing southwesterly flow locally into next week and keeping highs above normal in the 60s and 70s.

The cut-off low over the SW is finally progged to emerge by Tues- Wed, with a northern stream wave providing additional forcing, although whether or not these waves are phased remains to be seen. At any rate, rain chances return sometime during the Tues-Wed period (70-90% per the NBM). Given an unseasonably warm airmass and ample wind shear, will need to monitor the potential for additional strong to severe storms with this system.

Erwin

AVIATION

(For the 06z TAFs through 06z Friday Night) Issued at 1201 AM CST Fri Mar 6 2026

Foggy conditions with low ceilings with prevail overnight. Fog could become dense in spots, especially late tonight. A warm front will lift north across the region Friday morning. While this should help improve cigs/vsby as winds turn southerly, it will also introduce a chance for showers and storms, most favored near the Illinois River Valley. South winds will increase Friday afternoon with gusts picking up into the 25-30kt range. There is a chance (30%) for spotty showers and storms Friday afternoon and evening, but a better chance for showers and storms lies just beyond the current valid period as cold front approaches the region.

Deubelbeiss

ILX WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory until 9 AM CST this morning for ILZ031-037- 038-041>057-061>063-066>068-071>073.