textproduct: Chicago

KEY MESSAGES

- Heightened brush and grass fire weather threat through this evening

- Storm system to bring chances for showers and thunderstorms late Monday night through Tuesday. A few storms could be strong to severe, especially Tuesday afternoon/evening.

- Stormy weather pattern expected to persist into next weekend.

DISCUSSION

Issued at 248 PM CDT Sun Mar 29 2026

Through Monday:

Breezy southwesterly winds prevail this afternoon. Wind gusts have been steadily between 20 and 25 mph, though isolated gusts to 30 mph are possible prior to sunset. Relative humidity values have dropped into the 20-30 percent range. With these dry conditions present, there remains a heightened threat of brush and grass fires this afternoon and early evening. Winds are expected to diminish after sunset down to around 5 to 10 mph.

There is a weak mid level wave that will pass over central Illinois this evening. High res guidance has a weak vort lobe associated with this wave. It would not be surprising if there were a few returns that show up on radar, but with the amount of dry air present in the low levels, no precipitation is expected. As this wave exits early tomorrow morning, cloud cover should diminish toward daybreak.

An upper level long wave trough is expected to eject out of British Columbia overnight and move across the northern Plains on Monday. Meanwhile, a mid level shortwave trough is projected to eject out of the Colorado front range and move east through the day. Neither of these waves will provide precipitation chances for the area until Monday evening (more on that in the discussion below). A warm front out ahead of the midlevel trough will extend into Illinois and lift northward through the day. Winds will remain southwesterly, providing stronger warm air advection aloft, increasing 850 mb temps to around 15C. Surface temperatures are expected to increase to around 70F along the lakeshore and well into the 70s for the rest of the area (possibly near 80 the closer to west-central Illinois). High res guidance continues to show a pseudo-lake breeze, if not a back door front entirely, develop late tomorrow afternoon. Depending on the timing of it, this may impact overall high temperatures forecasted in Lake County Illinois and down to the city of Chicago, which may result in high temperatures being observed around the lunch hour, and then steadily falling into the evening.

DK

Monday Night through Sunday:

The main forecast focus is on potential convective trends and unseasonable warmth Monday night through Tuesday evening and then a likely rainy and blustery stretch late Wednesday through Thursday evening.

On Monday evening, a warm front will be north of most of the area, with the possible exception of portions of the Illinois lakeshore (most likely near and north of downtown Chicago). Here, the front may have sagged back south due to lake breeze enhancement, resulting in cooler conditions into the evening. With weak surface low pressure over southwest or southern Wisconsin, pressure falls should result in the lake reinforced front retreating back north by the late evening (assuming it makes inroads into NE IL Mon PM). This will be followed by increasing and at times gusty southwesterly winds overnight, with unseasonably mild temps in the 60s.

Regarding convective potential, another impressive EML plume will overspread the region, though initial antecedent dry low to mid levels will result in strong capping. A majority of the available guidance holds the capping through much of if not the entire night. Skeptical of any activity during the evening hours when the capping will be at its strongest. Overnight, most of the large scale forcing (500 mb up to jet level) will be well to our north. A 700 mb impulse crossing Iowa will result in increased mid-level moisture. However, with an overall lack of stronger forcing, it's unclear if isentropic lift from a robust low-level jet will be able to moisten up to the base of the cap to effectively tap into the modeled MUCAPE reservoir. It's also possible that the 700 mb wave is slow enough for any storms within the area to hold off until towards or beyond daybreak Tuesday.

With the above considerations in mind, capped maximum PoPs in the chance range near and north of I-80, highest at ~40-50% near and northwest of a Peru IL to Evanston line. The GFS and RRFS appeared to be too convectively active given the modest overall forcing. If the capping isn't breached, there's a play for primarily dry conditions through the night areawide. On the other hand, if any storms do occur, the very steep mid-level lapse rates may yield a threat for isolated severe hail and gusty winds, particularly amidst sufficiently supportive effective bulk shear (which is also uncertain). SPC's day 2 update maintained a 1/5 threat level (marginal risk) north of I-80, reasonable for now.

Tuesday's specific details are muddy at best due to continued modest/subtle/unclear forcing mechanisms until later in the day. Convective chances Tuesday morning, as alluded to earlier, may be tied to the aforementioned 700 mb impulse crossing the MS River and sufficient erosion of the lingering capping. Didn't have enough confidence for any notable changes to PoPs Tuesday morning through midday, and thunderstorm mention above slight chance/isolated. A cold front trailing from low pressure tracking towards Lake Huron and modest height falls should be able to touch off showers and at least scattered thunderstorms sometime during the PM hours, though there's also a good deal of uncertainty on timing specifics (afternoon vs. primarily towards and during the evening). Undoubtedly, prior convection in the morning, or a lack thereof, can be expected to modulate the afternoon and evening showers and storms. Outside of the highly uncertain convective forecast, Tuesday will feature unseasonable warmth and southwest winds gusting up to 30-40 mph. The extent to which official forecast highs in the mid to upper 70s north of I-80 and upper 70s to around 80 south of I-80 are realized will also be tied to shower and t-storm, and cloud cover trends.

Where temperatures end up will determine how much instability can be realized during and just after peak heating, pertinent to the threat for strong to severe storms. Still steep mid-level lapse rates (but not quite as steep as earlier in the day) and 30-50 kt of deep layer shear (unidirectional shear profile) may be supportive of isolated large hail and wind damage with any more intense storms. It does appear that veering southwesterly winds and fairly large temperature-dew point spreads should tend to limit a tornado threat.

The front will sweep across the area Tuesday night, shifting thunderstorm potential south of the area and bringing notably cooler conditions on Wednesday. Any break in the rain will be short-lived, especially with southward extent. Guidance has come into better agreement on widespread showers late Wednesday through Thursday, likely accompanied by some threat for storms as well. This period will need to be watched for corridors of heavy rainfall and some associated threat for flooding. Blustery northeast winds will make for a raw day areawide, particularly lakeside, on Wednesday. On Thursday, the exact path of surface low pressure will determine how far north a warm front can lift north, bringing temps back into the 60s (possibly even supporting a surface based severe threat). North of the boundary, northeast winds will continue to result in much cooler conditions (40s and 50s).

In the wake of the Thursday evening/night cold front passage, Friday should dry out for much of the area. Another round of showers and some thunderstorms then appears probable sometime in the Friday night through Saturday timeframe. At this time, next Sunday, Easter Sunday for those celebrating, appears that it should be quieter and cooler.

Castro

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 1230 PM CDT Sun Mar 29 2026

Key Aviation Messages for the current TAF period:

- Gusty southwest winds around 20 knots this afternoon.

VFR and dry conditions are expected through the TAF package. Winds remain out of the southwest with gusts around 20 knots expected through the afternoon and early evening before diminishing. With a strengthening low level jet over northwest Indiana, there is a marginal risk for low level wind shear, but kept it out of the KGYY TAF presently. Southwest winds will increase tomorrow again in the afternoon as mid level moisture increases cloud cover. Isolated gusts up to 20 knots are possible, but projected to be too infrequent to merit inclusion in the TAF.

DK

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.