textproduct: Chicago

KEY MESSAGES

- Periods of wet weather are probable during the Tuesday through Saturday period, which may include a threat for thunderstorms at times. Expect above average temperatures during this time, with the best chance for unseasonable warmth areawide on Friday.

DISCUSSION

Issued at 221 AM CST Sun Mar 1 2026

Through Monday Night:

An expansive 1036 mb surface high is descending across the Upper Midwest early this morning which will allow for continued northeast flow across the local area today. While winds have eased some, continued onshore flow from Lake Michigan will likely hold temperatures in the 30s across the area today with sub- freezing highs possible near the immediate lakeshore. The lake effect snow potential for today has diminished owing to the low cloud layer being even thinner than expected. Still can't rule out a few flurries at times today beneath any thicker stratus, however, no accumulation is expected.

Warm advective showers are expected to quickly expand in coverage across Kansas this afternoon coincident with the left exit region of the southern stream split upper jet. This feature will continue to track east across Missouri into central Illinois and Indiana this evening and overnight. While the overall trend has been toward the majority of the area remaining dry through tonight (owing to a dry low-level airmass in place), it remains possible that the northern periphery of this precipitation grazes the far southern portion of the forecast area (mainly south of US 24). This would likely be tied to a subtle ephemeral 850 mb fgen axis potentially ending up a bit farther north that could overcome the dry layer for a brief window. Have accordingly held onto low snow chances (20% in those areas) between 9 PM and 6 AM CST to account for this. While likely remaining south of the area it does look like a very narrow axis of heavier precipitation rates could occur on the north side of this system, potentially falling as a mix of snow and sleet.

The center of the surface high will shift east of the area on Monday allowing the surface flow to turn more southeasterly. This will bring a return of warmer than average temperatures to the area with highs in the low to mid 40s (cooler upper 30s along the IL shore). Looking ahead to Monday night, models continue to trend slower with the next weather system, potentially holding off until closer to daybreak. We will have to keep an eye on whether any spotty showers occur during the pre-dawn hours. If surface temperatures end up dropping below freezing during this time there could be patchy slick spots that develop. Given this is such a low probability scenario (currently under 15%), have held off on a formal mention of freezing rain with this update. See the discussion below for more details on the potentially more active pattern we are heading into.

Petr

Tuesday Onward:

A broader zonal flow regime with an embedded slow-moving trough over the central Rockies early in the week will transition to a much more meridional pattern highlighted by deep western troughing and eastern ridging for the second half of the week. Meanwhile, an expansive Bermuda High will foster a persistent feed of Gulf and Caribbean moisture toward the central CONUS through the period. This will ultimately result in a seasonably mild to at times unseasonably warm period with several rounds of rain and localized convection over the area. While axes of heavy rain appear likely over the mid-Mississippi and Ohio River valleys, it remains to be seen where those axes set-up and whether those axes align over the same location and result in flooding concerns.

Initially, broad low-level isentropic ascent combined with modest moisture transport will bring the first area of precip over at least portions of the area on Tuesday. Somewhat of a split flow regime and the "juiciest" low level air mass near a warm front across central Illinois and Indiana may tend to focus any higher rainfall amounts south of I-80. There does appear to be a plausible scenario in which a relative minima in rainfall or conceivably little/no rainfall materializes somewhere north of I-80 or I-88 where PoPs only peak in the likely (~70%) range.

Beyond the daytime hours of Tuesday, the spread in the ensemble suite, owing to the differences in the evolution of the western trough, offers less confidence on exactly when and where heavy rain axes develop. However, with PWATs around 1.5" (300% of normal), any pronounced wave emanating from the western trough will induce sufficient forcing to realize focused axes of heavy rain. The GEFS and to a lesser extent the Canadian ensemble system have remained on the faster side of the guidance envelope, which would entail rainy/inclement conditions for the Tuesday night-Wednesday evening period and then drying out on Thursday.

Meanwhile, if the consistently slower solutions advertised by about half of the ensemble suites (the ECMWF and UKMET ensembles) pan out, a good chunk of Tuesday night and Wednesday could be dry (especially with northward extent) before rain chances increase again late Wednesday night into Thursday. As a whole, while we can't ignore the consistent GEFS depictions with heavy rainfall totals farther north Tuesday night-Wednesday, the midweek focus may very well remain primarily across southern sections of the CWA and points south. On either side of the faster to slower spectrum with respect to rain trends Wednesday-Thursday, onshore flow from Lake Michigan will keep temperatures notably cooler within range of the marine layer inland propagation than for locales farther south and west.

We'll also need to keep an eye on the potential for more organized convection in or around the area Thursday PM and especially on Friday as a large portion of the western trough ejects toward the mid to upper-Mississippi River Valley. Even at this lead time, the various ensemble systems have a strikingly strong signal centered on Friday for a northward surge of anomalous dew points in the 50s to possibly 60F+ in spots coinciding with an approaching cold front and seasonably strong wind fields. The official forecast indicates likely PoPs area-wide Friday PM through Friday night and southeast of I-55 on Saturday morning, owing to a sizable portion of guidance members with a slower cold front passage. In the wake of the front, there should be a couple days of quieter, but still mild weather into the start of the 2nd week of March.

Castro/Kluber

AVIATION /12Z TAFS THROUGH 18Z MONDAY/

Issued at 504 AM CST Sun Mar 1 2026

There are no significant concerns through the TAF period. Lake induced 2500-3500 ft clouds into northeast Illinois and northwest Indiana will result in an occasional CIG this morning, with only mid and high level clouds thereafter. Steady northeast winds today will become light easterly overnight, then east-southeast Monday morning around 10 kt.

Castro

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 3 PM CST this afternoon for the IL and IN nearshore waters.