textproduct: Chicago

KEY MESSAGES

- Today will start out drab with mostly cloudy skies. A few showers or areas of drizzle cannot be ruled out through the afternoon.

- A fall storm system will move through the area Thursday and Friday bringing periods of rain showers and gusty northwesterly winds (the latter primarily on Friday).

- Frosty and locally freezing conditions are favored away from Lake Michigan Friday night into Saturday.

- After the brief period of chilly weather, there will be a warming trend this weekend into early next week.

DISCUSSION

Issued at 210 AM CDT Wed Oct 14 2026

Though Tonight:

Early morning GOES-19 water vapor imagery depicts a (nearly cut-off) upper-level trough propagating atop the Four Corners region. Several clusters of showers and thunderstorms are ongoing ahead of the trough associated with several upper- level vorticity maxima propagating atop an elongated baroclinic zone draped from the Southern Plains through the Lower Great Lakes. Locally, have been monitoring scattered storms across the area though relatively meager instability is maintaining a relatively generic quality intensity in spite of an otherwise favorable shear profile for organized convection. Meanwhile, a sprawling 1020mb+ surface high pressure system is building into the northern Plains, ahead of which an expansive region of low- level stratus is oozing southward through the Upper Midwest.

After daybreak, the aforementioned surface high pressure system will shift eastward toward the Upper Great Lakes leading to an increase in northeasterly flow across northern Illinois and northwestern Indiana. As a result, the low-level baroclinic zone in which showers and thunderstorms are ongoing will shift southward with time. Low-level onshore flow within a marginally unstable lake effect regime beneath a stout low-level inversion will reinforce low-level stratus through the morning and early afternoon hours, leading to a gray start to the day. Cannot rule out a few instances of sprinkles or drizzle near Lake Michigan or near US-24 (closer to the low-level baroclinic zone), so will maintain low-end PoPs (10-20% chances) generally east of I-39 and south of I-80 through the day. The high temperature forecast will hinge entirely on whether or not stratus is able to clear by early this afternoon, with high res guidance providing an affirmative "no." As such guidance can sometimes be too aggressive with stratus, will take the middle ground and advertise highs in the low to mid 60s north of I-80 and upper 60s to around 70 south of I-80 keeping in mind actual values may verify plus or minus a few degrees of our forecast.

Tonight looks quiet. Increasing upper-level cloud cover and continued onshore flow will hold overnight lows generally in the mid to upper 50s, warmest near Lake Michigan and near US-24.

Thursday into Friday:

Ensemble model guidance remains in excellent agreement that the southwestern US trough will eject northeastward and phase with a northern-stream trough screaming southeastward out of Canada. Am noting increasing agreement in the exact track and evolution of the resulting surface low, emerging from near Dodge City, KS Thursday morning to Kansas City, Missouri by early afternoon, passing directly over our area Thursday evening, and then continuing toward Southern Ontario overnight into Friday.

As the surface low approaches on Thursday, gradually increasing low-level isentropic ascent within the northward-moving baroclinic zone may support areas of drizzle and rain showers as early as daybreak before a higher coverage of showers slides overhead during the afternoon and evening hours. Suppose there may be a thunderstorm or two as well, particularly Thursday evening as a narrow instability axis attempts to lift northward ahead of a southeastward-moving cold front. The severe weather threat continues to look very low for our area both from a conceptual model framework as well as from explicit output (of nearly zero probabilities) from ML-based guidance. With our area smack-dab in the middle of the baroclinic zone, am anticipating quite a gradient in high temperatures on Thursday. Will undercut NBM guidance and feature highs in the upper 50s near and north of I-88 and lower 60s south of I-80. Taken altogether, Thursday looks fairly drab.

There remains agreement that an unusually strong surface high pressure system will quickly build into the central United States in the wake of the departing surface low leading to an impressive 40 to 45 mb pressure gradient directly over the Great Lakes on Friday. A somewhat bifurcated pressure rise couplet (a consequence of the upper-level troughs phasing directly overhead) suggest a one-two punch to winds on the backside of the system with a period of gusty northwesterly winds of 30 to 35 mph Friday morning followed by a stronger period of gusts of 35 to 40 mph during the afternoon and evening hours. Gusts may be higher (locally 45 mph) along the Lake and Porter Indiana shorelines of Lake Michigan where lake instability will support deeper mixing profiles.

Tumbling column temperatures by way of efficient cold-air advection will support a flare in diurnal instability leading to an expansive stratus deck. While ensemble mean temperatures support highs in the low to mid 50s, am noting quite a few individual members and deterministic counterparts showing explicit upper 40 degree highs across northwestern Illinois. Will (once again) undercut NBM guidance to feature highs in the lower 50s as a happy medium.

As the core of the northern-stream trough slides overhead (peak diurnal instability), can envision isolated to scattered showers accompanied by locally gustier winds moving through the area during the afternoon hours. Coverage of gusty showers should be maximized in northwestern Indiana by sunset where 850mb to marine airmass temperature differentials of 15 to 20C within the cyclonic shear side of the upper-level trough will push lake-induced instability toward 500 J/kg. (It'll be pretty raw out there along northwestern Indiana communities).

Friday night onward:

Lake effect rain showers should end overnight as inversion heights crash on the backside of the departing upper-level trough and the surface high pressure system slides into the middle Mississippi River Valley. With weakening winds and clearing skies, overnight lows will be poised to be the coldest of the autumn season so far with widespread readings in the low to mid 30s. The exception will be near Lake Michigan and along the I-65 corridor where lows will bottom out in the lower 40s thanks to to the continued influence of Lake Michigan and lingering lake effect stratus. Assuming no major changes to the forecast, will have to consider Freeze Watches for portions of the area before too long.

Thereafter, ensemble guidance advertises the surface high stalling over the Atlantic Seaboard and the northward retreat of the dominant upper-level jet into Canada supporting gradually rising temperatures and generally dry weather into next week. Ensemble meteograms of QPF from all ensemble suites depict a transition toward a somewhat showery pattern with seasonable temperatures during the the the last 5 to 10 days of the month.

Borchardt

AVIATION /18Z TAFS THROUGH 00Z FRIDAY/

Issued at 107 PM CDT Wed Oct 14 2026

Key Messages:

- MVFR ceilings will continue this afternoon.

- Rain is expected tomorrow with associated lowered ceilings and visibilities.

MVFR ceilings are being observed at all of our TAF sites at press time early this afternoon. Some lifting and/or scattering of this MVFR stratocumulus with time should allow for VFR conditions to return to at least a few of our TAF sites by this evening, but confidence in precise ceiling trends through tonight is not very high.

Regardless, ceilings will deteriorate tomorrow as a slug of rain associated with an incoming low pressure system pushes into the area from the southwest. A period of IFR ceilings is likely tomorrow afternoon, and there is a signal in forecast guidance for LIFR ceilings to be observed as well. MVFR or lower visibilities are also likely to be observed at times tomorrow during the steadier rainfall. Couldn't rule out some isolated lightning strikes occurring tomorrow afternoon, particularly near GYY and MDW, though the better thunderstorm potential should remain south of the terminals.

Winds through the TAF period are expected to retain an easterly component with magnitudes averaging out near or just under 10 kts.

Ogorek

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory from 4 PM this afternoon to 1 PM CDT Thursday for Winthrop Harbor to Wilmette Harbor IL.

Small Craft Advisory from 4 PM this afternoon to 10 AM CDT Thursday for Wilmette Harbor to Northerly Is. IL.

Small Craft Advisory from 4 PM this afternoon to 4 AM CDT Thursday for Northerly Is. IL to Michigan City IN.