textproduct: Chicago

KEY MESSAGES

- Windy and warm conditions today; areas of blowing dust in open areas this afternoon, especially south of I-80.

- Shower and thunderstorms expected tonight with a marginal (level 1 of 5) severe risk.

- Much colder temperatures expected Tuesday.

DISCUSSION

Issued at 258 AM CDT Mon May 4 2026

Through tonight:

Fairly complicated forecast today with strong/gusty winds leading to blowing dust issues in open areas, followed by an increasing threat of thunderstorms this evening along an approaching cold front.

Early this morning, a 984mb sfc low was located over western Ontario with a cold front trailing south and then southwest across northern MN west into the northern Plains. This low will track east to near Hudson Bay this evening as the cold front moves southeast to the western Great Lakes southwest to the mid-Mississippi Valley this evening. GOES total precipitable water imagery depicted an east-west axis of higher moisture from Missouri east into downstate IL with a sharp gradient to an unseasonably dry air mass to the north across our area.

Considerable sunshine today should allow for deep mixing, particularly across our northern CWA where air mass will be remain very dry. The deeply mixed boundary layer should tap into some higher momentum air off the sfc and result in another windy day with southwest winds gusting well over 30 mph at times this afternoon. Deep mixing should also result in dewpoints mixing out this afternoon, particularly north of I-80. I have undercut guidance dewpoints for today, but am concerned that they could end up a bit lower still.

There were numerous reports of blowing dust across central IL Sunday afternoon with some videos showing visibility getting down close to 1/4 mile in spots. Given that today should see fairly similar winds/gusts, would anticipate more blowing dust issues this afternoon, particularly southern CWA where things are still early in the agricultural cycle and there are a lot of open areas. In coordination with ILX, have opted to issue a blowing dust advisory for these areas today. Day shift may need to consider expanding the blowing dust advisory north into our western CWA where there are also a lot of open areas, but confidence was lower farther north so held off on the advisory north of I-80 for now and will let the day shift re-evaluate.

North of I-80 is where lowest afternoon relative humidity is expected, so will issue an SPS for these areas for the potential for blowing dust in open areas as well as a somewhat heightened fire danger. The area has greened up nicely, lessening the fire danger threat some, but given the very low RH and gusty winds, there could be a heightened fire risk associated with agricultural activity in fields that have not greened up.

Southwesterly flow should slowly advect the east-west oriented moist axis to our south northward today, but deep mixing will likely slow or stunt that northward progression some. Another narrow ribbon of higher atmospheric moisture is expected to pool ahead of the approaching cold front this afternoon. Forecast soundings ahead of the cold front across southern WI and northern IL look much more like soundings from the High Plains than the Mississippi Valley. Soundings exhibit the classic inverted V profile with LFCs 8-10k ft, suggesting that if any convection does develop along the cold front this afternoon over southern WI it will be high based and prone to producing gusty winds given the high DCAPE. Strong deep layer shear and steep lapse rates could also support a severe hail risk with the more intense storms.

As the front continues southeastward into northern IL this evening and that west-east moist axis shifts continues to slowly advect north, the two should begin to interact and result in an increase in coverage of showers and thunderstorms over our CWA this evening. Confidence in when convection develops and when/how quickly it increases in coverage is low, with the severe threat expected to gradually decrease in the evening with nocturnal cooling/stabilizing of the boundary layer.

Within the west-east moist axis across central IL, ample heating today is expected to erase convective inhibition and several CAMS are suggesting isolated-scattered thunderstorms could develop later this afternoon into early this evening across central IL, completely separate from the approaching front. While atmosphere moisture will be greater, forecast soundings still depict an inverted V, albeit a smaller one, so these storms could also produce strong/gusty winds. If storms develop and kick out some strong outflow, particularly if they cluster today, then potential would exist for a localized more severe dust storm. Similarly, if storms develop along the cold front to our northwest this afternoon, they could also kick out outflow with a threat for localized dust storm conditions farther northwest in our CWA as well.

Tuesday onward:

Front is expected to slow a bit later tonight as it moves toward central IL and becomes more parallel to the upper flow. Showers will likely continue north of the front and into at least our southern CWA into Tuesday morning as we get into the left exit region of 110-120kt southern stream upper level jet. The showers will slowly end from north to south Tuesday as the front and better forcing gradually shift southeast.

Much colder temperatures are expected Tuesday with highs generally in the 50s with cloud cover lingering into the afternoon. Winds off Lake Michigan could leave areas close to the lake mostly holding in the 40s Tuesday! Temperatures will moderate back closer to seasonable norms by the end of the week into next weekend. Northwest flow aloft should keep the better moisture shunted well to our south, so any weak disturbances rippling through the northwest flow should be moisture starved. If we do see any rain late week into the weekend it would likely only be isolated light showers and not rain out any outdoor activities.

- Izzi

AVIATION /12Z TAFS THROUGH 18Z TUESDAY/

Issued at 638 AM CDT Mon May 4 2026

Key Messages:

- Breezy southwesterly winds are expected once again today.

- Showers and scattered thunderstorms are expected at/near the terminals this evening (and as early as the late afternoon at RFD) as a cold front tracks through the area.

- A north-northwesterly wind shift is expected this evening behind the cold front.

Another period of breezy southwesterly winds is expected from mid-morning through this afternoon. Most gusts this afternoon will likely fall in the 25-30 kt range, but at least occasional gusts in excess of 30 kts appear plausible. Similar wind magnitudes yesterday kicked up dust from farm fields across various parts of Illinois, including near RFD, so couldn't completely rule out some visibility reductions from blowing dust at RFD today. If this dust were to get kicked up and consolidated by gusty thunderstorm outflow winds, then it's not entirely out of the question that some dust-driven visibility reductions could be observed at the Chicago metro terminals too, but this is an outcome that has far too low of a probability of occurrence to warrant a formal mention in the TAFs at this time.

A cold front will approach the area from the northwest late this afternoon and track across the terminals this evening. Showers and scattered thunderstorms are expected to develop along the front and will likely affect the terminals in some capacity this evening (and possibly as early as the late afternoon at RFD). The high-based nature of this convection will tend to favor VFR ceilings even during thunderstorms, but sub- VFR visibilities will still likely occur with the more robust downpours. Strong winds and a sharp wind shift to a direction between 270 and 010 may accompany the stronger storms this evening, but even if the gustier storms miss the terminals, then the incoming cold front will produce a wind shift to a north- northwesterly or northerly direction soon after the showers and storms have passed. Another period of showers/sprinkles may then occur well behind the front overnight into Tuesday morning. The latest model guidance largely favors the steadier rainfall and associated sub-VFR visibility reductions remaining south of the terminals Tuesday morning, but a slight northward shift could bring this steadier rain into at least MDW and GYY.

Ogorek

LOT WATCHES/WARNINGS/ADVISORIES

IL...Blowing Dust Advisory from 11 AM this morning to 6 PM CDT this evening for ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033- ILZ039-ILZ107-ILZ108.

IN...Blowing Dust Advisory from 11 AM CDT /noon EDT/ this morning to 6 PM CDT /7 PM EDT/ this evening for INZ001-INZ002- INZ010-INZ011-INZ019.

LM...Small Craft Advisory from 10 AM this morning to 7 PM CDT this evening for the IL and IN nearshore waters.