textproduct: Chicago

KEY MESSAGES

- Showers and some thunderstorms are expected for areas around and southeast of a La Salle to Chicago line early this evening. Some of these storms have the potential to become severe with primarily damaging winds southeast of a Pontiac to Gary line mid-evening.

- A windy stretch of weather is expected through Friday morning, with frequent gusts of 35 mph. Gusts may briefly reach 50 mph late tonight through around daybreak Friday.

- Another storm system will deliver a round of snow and rain, blustery winds, and falling temperatures Saturday through Sunday morning.

DISCUSSION

Issued at 254 PM CST Thu Jan 8 2026

Through Friday:

An expansive mid-latitude cyclone across the central CONUS will bring periods of convection and strong synoptic winds to the area late this afternoon through Friday morning. Robust WAA and low-level moisture advection are already well underway across the mid-Mississippi River Valley in response to an impressive kinematic field highlighted by a strengthening 140 knot upper- level jet nearing the area. The associated 991 hPa surface low currently over northwest Missouri will track northeastward to near Green Bay late tonight. Meanwhile, a somewhat sheared mid- level trough will brush the area to the northwest overnight.

Rain/Convection: Rapid low-level saturation within modest isentropic ascent has spread an axis of rain over much of northern Illinois this afternoon, with a current upstream gap in precip expected to slowly fill in over the next few hours. However, an active area of convection over Oklahoma this morning continues to quickly track northeastward across Missouri this afternoon in response to an axis of enhanced low-level convergence and slightly steeper mid-level lapse rates. The rapid transport of low-level moisture northeastward across Illinois through early evening will further steepen mid-level lapse rates and promote an elongated axis of convection along and southeast of a La Salle to Chicago line roughly in the 5-8pm window. Much of this initial convection should remain elevated (LPL around 900 hpa) over northern Illinois, including much of the Chicago metro. However, focus for any severe convection will turn to areas primarily southeast of a Pontiac to Gary line (and especially the far southeast CWA), in the 7-11pm window when convection has the potential to become surface-based. Of most interest is the low-level dew point field, with an arbitrarily critical value of 58-60F eroding enough surface- based CIN to foster at least some surface-based convection. Will need to closely monitor upstream trends over the next few hours, with the greatest concern for convective segments producing locally damaging winds and perhaps a brief tornado.

Beyond the evening convection, steeper low-level lapse rates and lingering low-level moisture will actually result in the potential for shallow surface-based showers/convection (no lightning). While deep-layer forcing will be less favorable under the deep dry slot aloft, cannot rule out some rotating gusty showers ahead of the cold front.

Wind: Outside of any convection, south winds gusting to 30 mph this afternoon will slightly back SSE while increasing this evening, with some gusts in excess of 35 mph. After the main convection clears the CWA toward midnight CST, the area will remain fully in the warm sector for several hours overnight. A small secondary 60-70 knot pre-frontal LLJ is expected to develop over northern Illinois during this time as the mid-level dry-slot takes hold over the area. Relatively steep low-level lapse rates by nighttime standards should allow at least some downward mixing of the stronger winds ahead of the front, with strong CAA further enhancing mixing as the cold front sweeps across the area late tonight. Meanwhile, an impressive isallobaric wind component highlighted by 10mb/hr or more pressure rises toward daybreak will provide added support for stronger winds. Expectation is that WSW winds veering WNW will gust 40 to 50 mph roughly in the 4 to 8am window, with the potential for a few gusts nearing 60 mph. A short-fused Wind Advisory may be needed if upstream observations early in the morning favor gusts closer to 50 mph instead of 40 mph. Winds will gradually veer N while diminishing mid-morning through the afternoon.

Temps: With strong WAA now in place, temps have pushed into the low 50s north to mid 50s south this afternoon. While precip may temporarily stunt temps at times through this evening, they should overall continue to rise to the mid 50s north to around 60 south. This will result in most locations ultimately recording calendar day highs for both the 8th and 9th around midnight. Temps will then fall through the 40s with the passage of the cold front late tonight, with temps generally in the low to mid 40s through the day Friday. Morning stratus should begin to erode in the afternoon, but temps would underperform if thicker stratus persists through the entire day.

Kluber

Friday night through Thursday:

Friday night into Saturday, a pair of upper-level waves -- one initially over the southern Rockies/southern Plains and another diving southeastward from Canada into the northern Plains -- will begin to phase over the Midwest. This phasing process will yield a sprawling upper-level low over the region, which will result in some showery periods in our area from Saturday morning through Sunday morning. As is often the case with phasing atmospheric waves (even just 36-48 hours out), some lingering uncertainties remain, namely with respect to precipitation types and the placement and magnitude of snow accumulations. However, many other aspects of this weekend's weather forecast are becoming clearer as model data continues to converge on a common solution.

The main wave of precipitation with this incoming system appears that it will come Saturday morning as increasing DPVA and upper-level diffluence tag team with low- to mid-level frontogenesis to induce a southwest-to-northeast oriented band of precipitation within an attendant baroclinic zone. Model guidance remains mixed on exactly where the main axis of precipitation will set up, but there is fair agreement across the 12Z guidance suite that most or all of our forecast area should see some sort of hydrometeors falling from the sky at some point Saturday morning. With near-surface temperatures expected to generally be in the low-mid 30s during this time, precipitation types remain a big question mark for most of the area. In general, though, rain will be more likely with southeastward extent, snow will be more likely with northwestward extent (and with time as a push of colder air spreads into the area), and there will also likely be a rain/snow mix line bisecting our CWA somewhere.

Where temperature profiles are cold enough (or dynamically cool to a sufficient extent) to support outright snow, stout frontogenetical forcing and 6-7C/km lapse rates through the dendritic growth zone should allow for snow to fall at a fairly steady clip within the heart of the snow band for up to 1-3 hours. Would not be surprised to see an axis of 1+" accumulations get laid out somewhere across our CWA Saturday morning with perhaps some slushy coatings occurring on some roadways wherever the snow falls steadiest. Otherwise though, lesser accumulations are expected, and the milder pavement temperatures leading into the event should tend to keep accumulations confined to grassy and colder surfaces.

Saturday afternoon into Saturday night, precipitation should transition into isolated to scattered snow showers as cold air advection steepens low- to mid-level lapse rates and the area becomes engulfed underneath the core of the upper-level low. Some additional dustings or coatings of snow could be observed with the most robust snow showers during this time as falling temperatures permit the snow to accumulate more easily, but this should tend to be more localized in scope. Increasingly blustery west-northwesterly winds during this time will also make these snow showers efficient at reducing visibilities, so motorists should plan on encountering sharply reduced visibilities in spots.

The last push of snow shower activity may affect northeastern portions of our forecast area Sunday morning, but otherwise, drier air being advected in from the northwest should put an end to the snow showers by Sunday afternoon. Temperatures in the mid teens to mid 20s Sunday morning may not climb much during the daytime on Sunday with the persisting blustery northwesterly winds, but if skies manage to clear out quickly enough, then some locations could still nevertheless see temperatures climb above 30F during the afternoon.

Early next week, a predominantly northwesterly flow pattern is expected to become established over the northern part of the CONUS. This will allow for a few clipper-type disturbances to be sent our way. The first of these disturbances looks to arrive sometime Sunday night or Monday, though it does not appear that it will saturate the tropospheric column enough for measurable precipitation to be observed as it shoots southeastward through the region. A better chance for precipitation should come with a follow-up wave in the Tuesday-Wednesday time frame, with both rain and snow appearing to be in play for precipitation types with that. While temperatures should trend above normal Monday into Tuesday, another cooldown is likely to occur in the wake of this mid-week system.

Ogorek

AVIATION /18Z TAFS THROUGH 00Z SATURDAY/

Issued at 1134 AM CST Thu Jan 8 2026

Primary aviation concerns include:

- Waves of showers will move over the terminals from mid- afternoon through the evening.

- Cigs will gradually lower to MVFR and then IFR this afternoon, and improve/scatter during the last 6 to 12 hours of the TAF period. - A period of southwesterly LLWS is expected overnight as flow at 2kft increases to nearly 60kt.

- Periods of gusty surface southwest winds are expected this evening and again toward daybreak Friday with peak gusts of 35 to 40 kt (if not higher, particularly around daybreak Friday).

Discussion:

A low pressure system currently centered in southern Kansas will lift toward Davenport, Iowa this evening and toward central Lake Michigan tonight. As the low approaches this afternoon, ongoing upstream waves of showers will reach the terminals and parade overhead through the evening as cigs lower to MVFR and IFR. Occasional drops in visibility to 3-5 miles may occur in the waves of showers. Winds should remain southeasterly through the afternoon and early evening with occasional gusts of 20-25kt. As the surface low approaches toward sunset, southwesterly low-level flow will rapidly intensify with flow at 2kft reaching nearly 60kt, requiring LLWS mention.

The convective band of showers with embedded lightning currently moving into western Missouri and Arkansas is expected to sweep across the terminals generally between 00 and 03Z this evening. Southwesterly wind gusts in excess of 35kt may occur with or between any convective element. A second round of convection may occur across the southern ZAU/C90 airspace near GYY between 03-05Z with a continued threat for southwesterly wind gusts in excess of 35 kt. Will handle the threat for convection in TEMPO groups, with a double TEMPO group at GYY where the threat for two rounds of convection is relatively highest.

Southwesterly surface wind trends behind the convective line and in the dry slot of the cyclone are an item of low confidence, as low-level lapse rates may modestly improve to continue tapping into the strong low-level wind field. It is easy to envision scenarios where wind gusts drop down to 25 kt if mixing does not occur, or remain near 35 kt if mixing continues. With flow at 2kft remaining near 50kt, felt continuing LLWS was justified through the overnight hours in spite of lower confidence in surface wind gusts trends. Cigs may attempt to break within the dry slot of the cyclone as well, but will maintain MVFR for now in favor of letting upstream trends inform changes.

Between generally 09 and 13Z, the cold front of the cyclone will race across the airspace accompanied by a broken band of showers and (a return of?) MVFR cigs. Impressive 3 to 6 hour pressure rises of 10 to 15 mb (if not higher) with an isallobaric gradient oriented from southwest to northeast across the airspace leverages increasing concern for a period of strong, if not damaging, winds potentially gusting 45 to 50 kt with the passage of the cold front. For now, will introduce PROB30 groups at all terminals for both -SHRA and southwesterly wind gusts of 40kt centered on the cold frontal passage, keeping in mind increases in magnitudes may be needed in later TAF packages.

Beyond daybreak, conditions will gradually improve through the morning. Winds will turn northwesterly and decrease in magnitude through the morning/early afternoon (gusts of 30-35kt easing after 15Z, with gusts subsiding entirely after 18Z). In addition, MVFR cigs will rise and scatter toward the very end of the TAF period.

Borchardt

CLIMATE

Issued at 254 PM CST Thu Jan 8 2026

Record warmth is forecast for Rockford and near record warmth for Chicago today, January 8 and Friday, January 9. The high temperature will likely occur around midnight between both dates.

The record high and record warm low temperatures for both Rockford and Chicago are included below:

Record Highs Record Warm Lows

January 8 January 9 January 8 January 9

Rockford: 55F (1965) 56F (2002) 36F (2008) 35F (2000)

Chicago: 63F (1965) 60F (1880) 45F (1876) 45F (1939)

NWS Chicago

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 9 AM CST Friday for Winthrop Harbor IL to Gary IN.

Small Craft Advisory until 3 PM CST Friday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.