textproduct: Chicago

KEY MESSAGES

- Unseasonably warm and breezy conditions through Tuesday.

- Potential for severe thunderstorms and heavy rain/flooding Tuesday afternoon into Tuesday evening.

- Shift towards more seasonable temperatures late week with additional chances of precipitation, some of which could be snow.

DISCUSSION

Issued at 248 PM CDT Sun Mar 8 2026

Through Monday Night:

Generally quiet weather will prevail through Monday night as a surface high over the southern CONUS holds control over our weather. Though, winds will remain on the breezy side as northern IL and northwest IN sits within a stout pressure gradient between the aforementioned high and a surface low moving through the northern Great Lakes. Therefore, expect southwesterly gusts around 30 mph this afternoon to give way to 20-25 mph gusts on Monday.

The breezy southerly will continue to advect in warmer air to the region so expect temperatures to remain above normal for early March. In fact highs on Monday will be in the lower 70s areawide under mostly sunny skies. Heading into Monday night, cloud cover will begin to increase ahead of our next storm system but temperatures look to remain mild in the lower to middle 50s.

Tuesday through Wednesday night:

While we enjoy the unseasonable warmth on Monday, a shortwave trough will be traversing across the Pacific Northwest as the upper low off the southern California coast ejects into the southwest CONUS and eventually the southern Plains Monday night. As this occurs, the northern stream wave is forecast to deepen and attempt to phase with the upper low in the southern Plains resulting in a broad trough across the central CONUS by Tuesday morning. The deepening and advancing trough is also expected to push the cold front (currently draped across the upper Midwest) into northern IL and northwest IN on Tuesday. At the same time, a weak surface low is expected to develop in the central Plains and begin to lift northward towards the Ohio River Valley which should push the aforementioned frontal zone back north as a warm front Tuesday afternoon.

Despite guidance being in generally decent agreement on this evolution with the upper waves/troughs, there continues to be notable differences between the GFS, ECMWF, and GEM guidance suites on where exactly the warm front will stall Tuesday afternoon. As a result, the temperature forecast on Tuesday is one of lower confidence as those north of the front will likely be sitting in the 40s and 50s (especially near the IL shore) while those to the south sit in the upper 60s and 70s. I did attempt to tighten up this expected temperature gradient across the area on Tuesday in our official forecast, but suspect temperatures are still too broad so expect further refinements to occur with subsequent forecasts.

In addition to the temperature gradient, the position of the warm front will also dictate the coverage and intensity of thunderstorms that are expected to develop Tuesday afternoon into Tuesday evening as the trough axis nears. Forecast soundings south of the front in the warm sector show steep mid- level lapse rates (around 7C/km) in addition to around 1000 J/kg of MLCAPE which in combination with the 60-65 degree dew points and ascent from the approaching surface low/trough axis will support scattered thunderstorms. Couple these ingredients with the 45-50 kts of effect shear and conditions in the warm sector look favorable for severe thunderstorms that will be capable of all hazards (damaging winds, large hail, and even tornadoes). On the other hand, those along and north of the front will likely have more limited low-level moisture to deal with and thus the instability will be largely elevated. Though, with the steep lapse rates and strong shear still expected to be present scattered strong to severe thunderstorms will be a possibility with the main threat of large hail and maybe locally gusty winds. Given the aforementioned uncertainty with the warm front's position knowing exactly which portions of northern IL and northwest IN sees which impacts remains unclear. Therefore, the broad slight (level 2 of 5) risk for the entire area and the focused enhanced (level 3 of 5) risk near and south of I-80 from SPC appears reasonable at this time.

Regardless of the severe thunderstorm coverage, all of northern IL and northwest IN will see some soaking rainfall out of this system with grand ensemble probabilities for at least a half inch of rain at 70-90% areawide. In fact, given the convective nature of this event localized amounts in excess of 1-1.5 inches are possible (40- 60% chance). While the highest ensemble probabilities for the 1+ inches of rain are favored south of I-80, the convective nature does make the exact location of the heaviest rainfall uncertain. Therefore, everyone should be prepared for heavy rainfall and localized flooding Tuesday afternoon through Tuesday night as this system moves through.

The main instability axis is expected to shift east of the area late Tuesday night which should allow the severe threat to diminish around midnight with just some isolated embedded thunderstorms through early Wednesday morning. However, widespread rain showers will linger through Wednesday afternoon as the aforementioned front moves through the area as a cold front. As a result, temperatures on Wednesday will be decreasing through the day with the daily high likely to occur prior to daybreak Wednesday morning. That said, the rain is currently forecast to end prior to the coldest temperatures arriving which should keep precipitation as rain, but if some of the faster solutions verify then some snow could mix in briefly across northern IL before precipitation ends. Though with pavement and surface temperatures forecast to be in the 40s as precipitation occurs snow accumulation is not expected.

Behind the front, winds will increase out of the northwest with gusts around 25-35 mph expected. These gusty winds will linger into Wednesday night as the cold advection keeps the atmosphere mixed, but gusts will gradually taper on Thursday.

Thursday and beyond:

A brief lull in the active weather is forecast for Thursday as mid- level ridging slides through the region. While the ridge will allow winds to become more southwesterly Thursday afternoon, the prevailing northwest flow aloft will aid in keeping temperatures in the more seasonable range with highs in the low to mid-40s.

Another shortwave is progged to dive out of Canada and traverse across the upper Midwest Thursday night into Friday which looks to bring more precipitation to the region. At the present time, guidance is in decent agreement that northern IL and northwest IN should be on the south periphery of this system so any precipitation looks to fall primarily as rain. In fact, the current trajectory keeps the bulk of any precipitation to our north in WI so if this solution holds true it appears that any precipitation may only impact the northern third to half of the area.

Heading into the weekend the forecast becomes much more uncertain as the aforementioned system Thursday into Friday is expected to stall a baroclinic zone across the region which will serve as the breeding ground for additional precipitation chances as shortwaves traverse the west-northwest flow pattern. Depending on where this zone establishes not only will determine the coverage of precipitation locally but also the precipitation type (rain vs. rain/snow mix). Given the great deal of uncertainty in placement of the baroclinic zone have opted to maintain the chances for rain/snow mix offered from WPC for Saturday and especially Sunday which seems reasonable at this range.

Yack

AVIATION /06Z TAFS THROUGH 12Z TUESDAY/

Issued at 1151 PM CDT Sun Mar 8 2026

Gusty SSW winds will continue tonight, primarily at ORD and MDW, with more infrequent gustiness expected at RFD, DPA, and GYY. A 50-55 kt LLJ will continue to yield at least marginal LLWS at the outlying TAF sites through daybreak, with more sporadic LLWS at ORD/MDW during lulls in gustiness. Breezy southwesterly winds will continue on Monday before diminishing during the evening.

The potential for MVFR/IFR cigs will increase late Monday night mainly near the Chicago-area terminals as moisture streams northward. At this time however, there is too much variability in the timing of various features to justify prevailing low cigs/vsbys during the extended ORD/MDW TAF, with the multi- model consensus pointing to conditions deteriorating near the end of the 30-hour window. Additionally, a shallow but very sharp cold front will push down the lake late Monday night/early Tuesday morning resulting in a northeast wind shift. Similarly, the timing spread is significant at this range, with most guidance suggesting FROPA may not occur until towards the very end or even just after the extended ORD/MDW TAF period.

Carlaw

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 4 AM CDT Monday for the IL and IN nearshore waters.