textproduct: Chicago

KEY MESSAGES

- Very strong and potentially damaging winds with peak gusts to around 60 mph will continue through this afternoon. A High Wind Warning remains in effect for most of the area.

- There is about a 30% chance for some areas to pick up a dusting of snow Saturday morning.

- Waves of thunderstorms may occur on Sunday. There is a Level 2 out of 5 threat for severe thunderstorms Sunday afternoon east of Interstate 55. The primary threat is damaging winds.

- A period of accumulating snow accompanied by northwesterly winds gusting over 35 mph may occur Sunday night into early Monday.

- A period of cold temperatures is expected Monday and Tuesday, with overnight low temperatures ranging from 5 to 15 below zero overnight into early Monday morning.

- The period of cold temperatures should be brief with warming temperatures by the end of next week.

DISCUSSION

Issued at 316 AM CDT Fri Mar 13 2026

Through Saturday:

Early morning regional surface analysis depicts a strong, wound-up ~986 mb surface low that is chugging its way eastward across the Upper Midwest. At 0800Z, its associated surface cold front was still arched back from western Wisconsin into east-central Iowa, but its fast forward speed has it on track to enter our western counties a little before sunrise. Looking aloft, a vigorous shortwave trough evident on GOES water vapor channel loops is powering its way southeastward towards the Lower Great Lakes and is pairing up with robust low-level warm air advection/isentropic ascent to drive a broad swath of precipitation through the region. In our forecast area, dry air in the low-levels should keep rain totals under 0.1" with most precipitation ending before sunrise (though the southern periphery of a rain/snow band wrapping around the low's center could graze some of our northern locales between sunrise and mid-morning).

It should be no surprise with a mid-latitude cyclone of this caliber that wind fields are quite strong through the depth of the troposphere across the region. We've already notched several 50+ mph gusts early this morning as the evaporative cooling of the overnight rain aided in the transfer of momentum from a screaming 70+ kt low-level jet down to ground-level, and intermittent 50+ mph south-southwesterly gusts may continue to be observed at times through remainder the night prior to the arrival of the aforementioned cold front. Behind the front, westerly winds should gust more regularly to 50-60 mph during the daytime today as post-frontal cold air advection steepens low-level lapse rates and allows us to more easily tap into the strong 850 mb flow within a more unstable planetary boundary layer and amidst robust pressure rises. The going wind headlines for our area thus look to be in good shape, and was not planning to make any changes to them this morning.

Behind the low/shortwave, a sharp northwest-southeast oriented low- to mid-level baroclinic zone will get laid out from the central/northern Plains down through the Ohio River Valley. Frontogenesis within this baroclinic zone will likely cause an elongated snow band to develop to our west late tonight. This snow band would then potentially spread into portions of our forecast area towards daybreak and continue through Saturday morning before dissipating or exiting our area to the north and east. At this time, model guidance suggests that dry low-level air, somewhat ephemeral frontogenesis, and limited to non- existent additional forcing support should preclude much more than perhaps a few streaky dustings of snow accumulation being observed in our forecast area with this potential snow band. However, lapse rates are progged to be somewhat steep within the dendritic growth zone (which should reside squarely within the cloud layer), and have seen similar f-gen snow events overperform relative to model guidance, so can't completely discount the possibility of up to an inch or so of localized snow accumulation being observed across a narrow corridor or two within our CWA.

Ogorek

Saturday Night through Thursday:

This weekend, an upper-level shortwave currently south of Alaska will undergo significant amplification wile diving southeastward across the central United States. Ensemble model guidance is in excellent agreement that the initial surface cyclone will develop in the lee of the Rocky Mountains near the WY/SD/NY border region Saturday and rapidly deepen while moving generally eastward into the Great Lakes Sunday into Monday. In fact, GEFS/EPS/CMCE all exhibit relatively tight clustering of path of the low near or directly over northern Illinois or southern Lake Michigan on Sunday, setting the stage for a rollar-coaster in weather conditions in our area over a roughly 24 to 36 hour period of time.

As the low deepens while approaching our area Saturday night, increasing low-level warm air advection will facilitate temperatures stagnating if not warming through the night. While the low-level baroclinic zone and a developing warm frontal zone will be moving northward through time, will have to watch for any lead subtle shortwave to excite elevated convection or even an early start to mid-level frontogenesis, especially considering mid-level lapse rates will be steep. Precipitation type could favor anywhere from a cold rain to heavy wet snow, including graupel and hail. For now, will offer a gradient in PoPs across the area Saturday night ranging from around 20% near US-20 to around 80% at the Wisconsin State line. This will be a period to refine going forward.

Low-level warm air advection will only intensify after daybreak Sunday, allowing for temperatures to skyrocket into the upper 50s (north) to mid 60s (south) in spite of heavy cloud cover. In fact, impressive pressure falls ahead of the surface low (on the order of 10mb/6hr) will support strong southerly winds, with more aggressive mixing profiles supporting widespread wind gusts of 40 to 50 mph. There is a subtle signal in extended RRFS and experimental MPAS WRFs for the passage of a mesoscale gravity wave through the area Sunday morning near the IL/WI border, which with the continued steep mid-level lapse rates may support a somewhat unexpected band of storms.

During the late afternoon and evening hours, the surface low pressure system will move directly overhead or close by. With a growing signal for a ribbon of low-level moisture to race northward into our area ahead of the approaching cold front beneath an intense low-level wind field (850mb flow progged to increase toward 50kt), am growing increasingly concerned that a narrow band of low-topped convection may develop and efficiently transport damaging to destructive winds across the area. At this point, such a threat appears highest along and east of I-55 where extended CAM guidance supports SBCAPE climbing above 100 J/kg. In scenarios where the surface low verifies deeper and further northwest, even higher values of instability may materialize and support a more widespread and potentially higher impact damaging wind event. For now, the Storm Prediction Center has introduced a Level 2/5 threat area for severe weather east of I-55 for Sunday which seems quite appropriate given current ensemble mean fields.

Sunday night into Monday, the low pressure system will lift into Michigan as temperatures tumble in our area behind the cold front. We continue to see a signal for the backside of the developing comma head snow region to at least graze if not outright move across our area. Considering strong pressure rises (on the order of 10mb/6hr) will force similarly strong northwesterly winds gusting 35 to 45 mph (if not higher), any falling snow could prove problematic with low visibility and quick accumulations on roadways. With continued spread in guidance in the strength, location, and duration of snow on the backside of the system, as well as generally low probabilities for at least 6 inches of snow (grand ensemble probabilities are <50% areawide), did not have enough confidence that warning- level impacts may be in play to justify hoisting a Winter Storm Watch with the out going forecast package. (The probability of "major" or a level 4 out of 5 on the probabilistic WSSI scale is only 10 to 30% across our area). With that said, can easily envision the need for a Winter Weather Advisory for parts of the area Sunday night into Monday if the signal for wintry weather comes to fruition.

Monday into Tuesday will feature a brief hit of chilly air as unseasonably cool 850mb temperatures bottoming out near minus 20C slosh into the region behind the departing storm system. Highs both days are poised to stay stuck in the 20s. Meanwhile, lows Monday night are expected to fall into the single digits. With a continuation of breezy northwesterly winds, wind chills Monday night are expected to fall to 5 to 15 below zero areawide. Depending on the actual wind direction, would also expect lake effect snow to at least graze northwestern Indiana at times, as well. Thankfully, the polar plunge looks to be short-lived as ensemble guidance advertises the development of anomalously strong upper-level ridging and associated warming temperatures by the end of next week.

Borchardt

AVIATION /12Z TAFS THROUGH 18Z SATURDAY/

Issued at 602 AM CDT Fri Mar 13 2026

A strong low pressure system continues to move through the Great Lakes and is driving a cold front through the ZAU airspace at press time. Winds will soon shift to westerly (wind direction 270 to 290) at all terminals with gusts increasing and prevailing in the 45 to 55 kt range through early afternoon. MVFR cigs based between 2000 and 3000ft will also spread over the terminals, with highest confidence in prevailing conditions at RFD/DPA/ORD/MDW. Cigs should tend to scatter while rising in height this afternoon.

Winds will be slow to subside this afternoon, but they will decidedly lose their punch after sunset. As a surface high pressure system works into the area overnight, wind magnitudes will become nearly calm before adopting a general southeastward direction by the end of the TAF period. Mid-level clouds will thicken with time overnight.

Borchardt

LOT WATCHES/WARNINGS/ADVISORIES

IL...High Wind Warning until 4 PM CDT this afternoon for ILZ003- ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013- ILZ019-ILZ020-ILZ021-ILZ023-ILZ103-ILZ104-ILZ105-ILZ106- ILZ107-ILZ108.

Wind Advisory until 6 PM CDT this evening for ILZ032-ILZ033- ILZ039.

IN...High Wind Warning until 4 PM CDT this afternoon for INZ001- INZ002-INZ010-INZ011.

Wind Advisory until 7 PM EDT this evening for INZ019.

LM...Storm Warning until 4 PM CDT this afternoon for the IL and IN nearshore waters.

Gale Warning from 4 PM this afternoon to 10 PM CDT this evening for the IL and IN nearshore waters.