textproduct: Chicago

KEY MESSAGES

- Southerly winds will become breezy (gusts 30 to 35 mph) amidst scattered showers and isolated thunderstorms tonight.

- The combination of dry conditions, gusty west winds, and warm temperatures will lead to a threat for brush fires on Wednesday, especially toward the Wisconsin state line. A Fire Weather Watch is in effect for areas north of I-80 in IL.

- Another storm system will arrive on Thursday accompanied by arcs of showers and thunderstorms. Another push of breezy winds will follow into Friday.

- Temperatures will trend cooler toward or below the average for this time of year Friday and through the weekend.

UPDATE

Issued at 927 PM CST Tue Feb 17 2026

Evening surface analysis depicts a 985mb surface low over southeastern SD beneath a negatively-tilted upper trough axis swinging from the Plains into the Midwest. Transient shortwave impulses/vort lobes extending east from the low managed to churn up a few bands of light showers that survived through a low level dry layer to fall on parts of our CWA this evening. Regional radar imagery shows a plume of virga showers over central IL which may have an easier time reaching the surface as it propagates over the local area with slightly more low level moisture available up this way. Efficient southerly upglide in the storm's warm sector will bring improvements in moisture availability over the next several hours; dewpoints have recently climbed into the lower 50s across central IL and northern IL is expected to follow suit overnight. We're still assessing the potential for additional showers through the night and the possibility of an embedded thunderstorm or two.

Attention is on an area of scattered showers out near the Missouri River and crossing into Missouri and Iowa deeper into the true warm sector. A number of camps suggest these showers will expand in coverage, or at least maintain their scattered nature, across the Mississippi before falling on the local area during the overnight as the warm sector expands deeper over the region. Coverage remains fairly uncertain, but highest coverage and generally greatest chances are favored roughly along and north of I-80.

With the overnight shower potential, it's not out of the question to see a few embedded lightning strikes. Amid the low level warm advection, we'll see mid level lapse rates steepen up a bit overnight and allow for as many as a few hundred joules of elevated CAPE to develop. Enough attendant forcing should be around to give parcels a shot at realizing this instability, and an impressive 30 to 40 kt of effective shear through the low levels will give any developing updrafts an extra boost. Luckily, profiles quickly dry out toward daybreak before the mid level cooling kicks in and lapse rates really steepen up for the morning, otherwise we'd be looking at a much more appreciable thunder potential. Instead, I'd imagine it'd be difficult to get more than a handful of strikes here and there, if any. Time window for any thunder potential is roughly 1-2 AM through about 5-6 AM. Made no changes to the inherited slight thunder chances in the forecast.

Latest high res guidance depicts a period of some pretty gusty winds overnight, particularly across our south as a low level jet focuses over central IL bringing nearly 40 kt of flow down to 925 mb. If that materializes, even shallow BL mixing could easily pull 30+ mph gusts down to the surface. Still looking awfully breezy tomorrow as well in the wake of this storm's cold front. Westerly winds will really take off around mid-morning with 35 to 40 mph gusts expected from late morning through the afternoon. The strongest winds are favored roughly near and north of I-88. While gusts to 45+ mph are certainly in the cards, confidence is not quite there to warrant issuing a Wind Advisory just yet; will allow the overnight shift to get one last look.

No real changes in thinking for the fire weather concerns tomorrow. The going Fire Weather Watch may need to be upgraded to a Red Flag Warning for portions of our area overnight as we get a better handle on daytime dewpoint trends.

Updated forecast has been published.

Doom

DISCUSSION

Issued at 228 PM CST Tue Feb 17 2026

Though Wednesday Night:

A broad upper trough continues to spiral over the western CONUS with a leading shortwave trough starting to eject into the central Plains. Ahead of the shortwave a surface low is developing over the Dakotas and northern NE with an associated frontal boundary stretching from the low eastward to southern Lower MI. Presently the weather across northern IL and northwest IN is rather tranquil with just some mid-level clouds and mild temperatures in the mid to upper 50s. However, that will change through the evening as the aforementioned shortwave and surface low pivot eastward into the Upper Midwest and Great Lakes. As this occurs the frontal boundary in far northern IL will begin to lift into WI with as an area of rain develops along it. While this rain will likely stay well north and east of our area tonight, some scattered rain showers are expected to develop after 9 PM ahead of an approaching dry-line and linger through the early morning hours on Wednesday. Forecast soundings across northern IL and northwest IN tonight continue to show some steep lapse rates developing overhead (6-8C/km) which could result some embedded thunderstorms especially after midnight. Though, with moisture expected to be a limiting factor (dew points only around 50F) coverage of any thunderstorms looks to be very hit and miss (20% chance of occurrence). Outside of the rain, winds will also increase through the night with gusts around 25-30 mph expected.

Heading into Wednesday, the aforementioned dry-line will move through the area and allow any lingering rain to quickly conclude. In the wake of the dry-line dew points will also quickly tank into the lower 20s (possibly even the upper teens in places) which in combination with temperatures warming into the mid 60s will result in RH values around 15-25%. These conditions in combination with gusty west-southwest winds around 30-40 mph will result in an elevated fire danger Wednesday afternoon. While meteorologically these conditions are very close to our local Red Flag Warning criteria, recent observations from fire partners indicate that fuel moistures vary across the area and may be more of a limiting factor. Therefore, we have opted to issue a Fire Weather Watch for our IL counties north of I-80 where confidence is highest in the highest winds and lowest RH values being observed for now. Regardless, any burning Wednesday should be postponed and extreme caution should be used when using or discarding any burning materials.

The gusty winds will gradually subside after sunset Wednesday evening as mixing ends. Dew points will also slowly recover Wednesday night as another shortwave ejects into the central Plains with cloud cover expected to increase as well. While the clouds should limit the cooling of temperatures Wednesday night, overnight lows are still forecast to dip into the upper 30s and lower 40s.

Yack

Thursday into Early Next Week:

Wednesday night, a series of upper-level shortwaves (currently dropping southward along the Pacific Coast) are expected to eject east-northeastward across the Rocky Mountains and induce the development of a low pressure system in the central Plains. Ensemble model guidance remains in fair agreement that the center of the low pressure system will then track from near Kansas City, Missouri Thursday morning toward Davenport, Iowa Thursday evening. Provided coverage of any early showers and thunderstorms is kept to a minimum (more on this in the next paragraph), afternoon high temperatures in our area on Thursday will be poised to rocket back into the mid 60s, some 20 to 25 degrees above the average for this time of year.

The continued eastward advection of an EML plume emanating from the high plains, increasing low-level warm air advection, and the arrival of the first of several shortwaves may spur the development of isolated to scattered showers and thunderstorms as early as daybreak Thursday across parts the area. Coverage of showers and storms should increase within northeastward-moving arcs during the afternoon and evening hours as the primary shortwave arrives. As can be expected 48 to 72 hours in advance, it's tough to have confidence in the exact structure, location, and arrival time of what will probably be a somewhat narrow surface-based warm sector to the east of a rapidly-advancing dryline and/or pre-frontal trough along the southeastern flank of the low pressure system. With that said, any overlap of the incoming upper-level jet (to support deeply-sheared kinematic profiles) and really any instability warrants watching for supercell structures (including during the morning hours). Stay tuned.

Behind any convective activity Thursday evening, an initial push of southwesterly winds will be overcome by the cold front toward daybreak Friday and an associated increase in westerly winds. A building 1020mb surface high pressure system in the central Plains will facilitate respectable pressure rises on the order of 10mb/6hr, supporting gusts in the 30 to 40 mph range during peak heating on Friday. If higher-end scenarios within the ensemble envelope were to materialize (deeper low pressure system, stronger high pressure system), will have to increase gust magnitudes beyond our current forecast (EPS mean gusts are closer to 45 mph). Stout cold air advection will also mark the (temporary?) end of the recent stretch of much above-average temperatures, with afternoon temperatures on Friday only poised to reaching the upper 30s (northwest) to mid 40s (southeast).

Forecast confidence lowers from this weekend onward as the door opens for the complex interaction of several upper-level shortwaves across the general Great Lakes region. With that said, temperatures this weekend look to remain near or below average. Ensemble model guidance hints at the cool-down being somewhat short-lived as an upper-level low stalls off the Pacific Coast and establishes another southwest flow regime across the central US to close the month.

Borchardt

AVIATION /06Z TAFS THROUGH 12Z THURSDAY/

Issued at 1138 PM CST Tue Feb 17 2026

Key Aviation Forecast Messages for the 06Z TAFs:

- Periods of rain/showers overnight, with IFR cigs and occasional MVFR/IFR vis in RA/BR. Localized LIFR cigs especially for KRFD.

- Breezy south-southeast winds overnight with gusts 25-30 kts, becoming southwest with a cold frontal passage around daybreak Wednesday.

- Very strong west-southwest winds Wednesday, with gusts 30-40 kts especially in the afternoon. Highest gusts, potentially in excess of 40 kts, most west/northwest of Chicago terminals (KRFD) in the afternoon.

Deep 985 mb surface low pressure was located near the SD/MN border late this evening, with an occluding cold front pushing eastward across the mid-Missouri River Valley. Tightening of the surface pressure gradient southeast of the low was producing breezing south to south-southeast winds across the terminals, with gusts 25-30 kts (isolated higher) expected overnight. Areas of rain/scattered showers were also lifting northeast across the forecast area in a region of warm/moist advection ahead of the low and cold front, and will persist through the predawn hours. Steepening lapse rates aloft will support a slight chance (<25%) of isolated embedded TS predawn, though coverage appears to be fairly low and focused primarily west/northwest of the terminals. Extensive IFR and patchy LIFR ceilings are expected prior to cold frontal passage, with some MVFR/IFR visibilities in RA/BR.

Surface cold front moves through the area in the 11-13Z period Wednesday morning, with a wind shift to southwest and rapid improvement to VFR conditions. Winds are expected to increase significantly during the day, with gusts of 35-40 kt by midday. Strongest winds look to be during the early through late afternoon hours, with gusts in excess of 40 kts likely at times, especially northwest/west of Chicago (notably KRFD). Some high- res model guidance (RAP/HRRR) mix very deeply Wendesday afternoon, which could support gusts around 50 kts, though confidence that mixing will be that deep is low at this time. Did increase gusts above 35 kts for Chicago sites and to 40 kt at RFD to match latest trends. Gusts should decrease quickly with sunset, though may be breezy for a time at least through midnight.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES

IL...Fire Weather Watch from 9 AM CST Wednesday through Wednesday evening for ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010- ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022.

IN...None. LM...Small Craft Advisory until 6 PM CST Wednesday for the IL and IN nearshore waters.