textproduct: Chicago

KEY MESSAGES

- Warmer and occasionally wet weather will materialize from the middle of the week through the middle of next week.

DISCUSSION

Issued at 138 PM CST Sun Mar 1 2026

Through Monday Night:

A surface high pressure system is centered over the Upper Great Lakes and continues to serve as the primary influence on weather in our local area. East to northeasterly winds on the southern side of the surface high continues to provide a stead feed of relatively dry onshore flow from Lake Michigan. Hence, in spite of mostly sunny skies, high temperature this afternoon will top off in the mid to locally upper 30s.

Upper-level cloud cover will increase this evening as an upper- level wave propagates eastward toward the Ohio River Valley. At this point, we still favor a dry forecast for our area given (1) the strongest DCVA associated with the wave will focus well south of our area, and (2) the aforementioned surface high pressure system will continue to feed dry low-level air through the area. As a result, any reflectivity echoes that develop within regions of mid-level frontogenesis south of Interstate 80 this evening and tonight should be relegated to virga. Overnight lows look to settle in the low to mid 20s.

Tomorrow, the surface high pressure system will shift toward the northeastern United States leading to winds gradually turning from east to southeasterly. Modest warming of the column via mid-level subsidence in tandem with largely opaque but still somewhat sunny conditions will help boost high temperatures to the mid to upper 40s. The exception will be along the Illinois shoreline of Lake Michigan where southeasterly onshore flow will hold readings in the upper 30s. Cloud cover will thicken tomorrow evening as low-level warm air advection ramps up ahead of a series of storm systems organizing in the central US. Chances for showers will increase after midnight and especially after daybreak Tuesday, as discussed below.

Borchardt

Tuesday Onward:

A mild and active stretch of weather is expected across the central CONUS midweek into the upcoming weekend as zonal flow early this week transitions to deep troughing across the west half of the CONUS. An expansive Bermuda High will foster a persistent feed of Gulf and Caribbean moisture toward the central CONUS through the period, resulting in an unseasonably moist airmass (PWATs over 300% of normal at times) in and around the region. While this pattern favors axes of heavy rain over the mid-Mississippi and Ohio River valleys, it remains to be seen where those axes set-up and whether they align over the same location and result in flooding concerns.

Broad low-level isentropic ascent combined with modest moisture transport will bring the first area of precip over at least southern portions of the area on Tuesday, with the greater focus for a more robust swath of rain with embedded elevated convection over the southern half of Illinois. However, a weak, low-amplitude disturbance quickly tracking from Montana to the western Great Lakes may result in a broader light rain shield and areas of drizzle over most of the area Tuesday morning into the afternoon.

The spread in the ensemble camps remains high Wednesday through Thursday, owing to the differences in the evolution of the western trough. However, those camps are coming into better agreement that a lead wave over the central Rockies will cross the southern Great Lakes on Thursday. It remains to be seen if higher precip rates (enhanced by waves of convection) will focus over or south of the forecast area late Wednesday night into Thursday, but latest trends are beginning to favor at least higher chances of appreciable rainfall amounts over the southeast third of the area during this time.

We continue to monitor for the potential for more organized convection in or around the area 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 60 to 80 percent PoPs area-wide Friday through Friday night and southeast of I-55 early Saturday morning, owing to a sizable portion of guidance members with a slower cold front passage.

Kluber/Castro

AVIATION /00Z TAFS THROUGH 06Z TUESDAY/

Issued at 500 PM CST Sun Mar 1 2026

There are no significant aviation weather concerns. A BKN-OVC cloud layer around 12 to 16 kft will gradually shift south of the terminals this evening. ENE winds around 10-15 kts will continue tonight and will become southeasterly through late tonight and into Monday morning. VFR conditions are expected through the TAF period.

Carlaw

LOT WATCHES/WARNINGS/ADVISORIES

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