textproduct: Chicago

KEY MESSAGES

- Red Flag Warning in effect this afternoon for areas along and west of the Fox Valley and I-55 due to the combination of very dry conditions, gusty west winds, and warm temperatures leading to a very high threat for the spread of brush fires.

- Another storm system will arrive on Thursday accompanied by arcs of showers and thunderstorms (some strong to severe storms possible). 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 858 AM CST Wed Feb 18 2026

A few changes were made to the forecast this morning:

(1) The Red Flag Warning was expanded to Lake, Cook, DuPage, Will, and Kankakee counties in northeastern Illinois. In spite of the 0.05 to locally 0.15" of rain that fell last night, fire weather partners indicate that the rapid drying of the column by this afternoon will cause fine fuels such as grasses to dry out to burnable levels. Activities that may generate sparks or involve open flames are highly discouraged in the Red Flag Warning area, as they may lead to uncontrolled brush fires.

(2). The Wind Advisory was expanded for all counties along and north of Interstate 88. Mixing profiles from the latest NAM, HRRR, RAP, and GFS ubiquitously indicate 40 to 45 kt of flow at the top of the boundary layer across far northern Illinois this afternoon. Accordingly, suspect there will be at least periodic gusts tagging 45 mph this afternoon as far east as Lake Michigan. Meanwhile, closer to the Wisconsin state line and west of Interstate 39, would not be surprised to see gusts top 50 to 55 mph where locally 50 to 55 kt of flow will be present at the top of the channel.

The rest of the forecast appears to be right on track. Temperatures are off to the races and should top off in the mid to locally upper 60s today. Updated products are being sent.

Borchardt/Yack

DISCUSSION

Issued at 315 AM CST Wed Feb 18 2026

The primary weather concern in the near term (today) continues to focus on what is expected to be a significant Fire Weather day across a good chunk of northern IL, particularly along and west of the Fox Valley and I-55. With this in mind, we opted to convert most of the Fire Weather Watch to a Red Flag warning, mainly for areas along and west of the Fox Valley and I-55. This area looks to solidly meet Red Flag criteria for several hours this afternoon (RH <25%, sustained winds 20+ mph and 10 hour fuel <9%). Areas farther east are also likely to meet the first two criteria for a couple hours this afternoon, but for a shorter duration. Additionally, the 10 hour fuel moisture threshold will be more difficult to obtain, especially considering the wetting rain (~0.1") that has occurred overnight. It is for these reasons that we opted to cut off the eastward extent of the Red Flag Warning, going instead with a SPS (Special Weather Statement) to message the lower, but still heightened, fire threat across the remainder of my northeastern IL counties.

Dewpoints are expected to tank into the 20s from west to east across northern IL late this morning and afternoon following the passage of frontal boundary/quasi-dry line. This will result in afternoon RH percentage values falling as low as 15-20% (lowest in the Red Flag Warning area) as temperatures warm into the mid to upper 60s. It is quiet rare to have RH values fall below 20% in this part of the country at any time of year, let alone in mid February. Unfortunately, these very dry conditions will be accompanied by strong gusty westerly winds (gusts of 35 to 45 mph) during peak heating this afternoon, making for elevated to Critical Fire Weather conditions. Accordingly, outdoor burning is not recommended, particularly in the Red Flag area.

The expectation of the strong gusty winds this afternoon has also prompted us to issue a Wind Advisory for a small portion of our area today. While it will be a windy day area-wide, the strongest winds, with gusts around 45 mph, are expected across northwestern IL in closer proximity to a weakening ~990 mb surface low over MN. Accordingly, in collaboration with NWS DVN, we have added Winnebago and Ogle counties to this Advisory. The remainder of northern IL and northwestern IN can expect gusty winds more in the 35 to 40 mph range this afternoon. These gusty winds are expected to abate fairly quickly following sunset early this evening.

KJB

Thursday into Early Next Week:

Forecast attention will also be focusing in on the evolution of a series of upper-level impulses, currently rounding the base of the trough over southern California. These are expected to eject east-northeastward across the Rocky Mountains later today into this evening, resulting in lee cyclogenesis over the front range of the Colorado Rockies. Ensemble model guidance remains in agreement that the center of this developing surface low will then track from near Kansas City, Missouri Thursday morning toward Davenport, Iowa Thursday evening.

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 around 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 36 to 48 hours in advance, it remains tough to have confidence in the exact structure, location, and arrival time of what is likely to be a 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/KJB

AVIATION /18Z TAFS THROUGH 00Z FRIDAY/

Issued at 1130 AM CST Wed Feb 18 2026

West to southwesterly winds will continue to increase in magnitude over the next few hours as the dry slot of the synoptic scale cyclone centered to our northwest races into the Lower Great Lakes. The expectation remains for wind gusts to peak in the 35 to 40kt range at ORD/MDW/GYY/DPA and 45 to 50kt range at RFD between 19 and 00Z this afternoon. After sunset, wind magnitudes should quickly drop off both as the synoptic scale cyclone weakens and surface decoupling commences. Skies will remain clear through this evening.

Tonight, a surface pressure ridge will slide into the Great Lakes causing winds to become light and variable. Wind direction should settle on a generally easterly direction by daybreak and gradually increase in magnitude through the morning hours as a warm front takes shape across central Illinois and Indiana. Do have some concern that increasing low-level moisture advection atop the front will facilitate the blossoming of low (500-1000ft) stratus north of the warm front from mid-morning through early afternoon, especially as flow increases off Lake Michigan. So, will tuck in a SCT007 into the outgoing TAF package at all TAF sites toward the end of the TAF period. Mid- level clouds will thicken throughout the day regardless of the development of any low stratus.

In terms of the threat for convection tomorrow... A pristine EML plume will advect eastward into the Great Lakes tonight into tomorrow morning in advance of the next shortwave propagating in the broad southwesterly flow aloft. Gradually increasing low- level warm air advection beneath the EML plume and the arrival of any lead "ripple" may support isolated to scattered convection in the ZAU airspace as early as daybreak, as hinted by NAM3/ECMWF/WRF NSSL guidance. For now, the probability of morning convection somewhere in the 10 to 15% range, so will withhold mention in the outgoing TAF package. Perhaps a better opportunity for convection will be during the late afternoon and early evening hours as a hybrid prefrontal trough/dryline (stronger forcing) races northeastward across the area. Will go ahead and introduce PROB30 groups at ORD/MDW focused on the 21-00Z window tomorrow afternoon for such a threat, keeping in mind refinements in timing may be needed in later TAF packages.

Borchardt

FIRE WEATHER

Issued at 315 AM CST Wed Feb 18 2026

Elevated to Critical Fire Weather Threat Today...

A significant early season fire weather threat exists today across a good chunk of northern IL. This is particularly the case for areas along and west of the Fox Valley and I-55, where the Fire Weather Watch has been upgraded to a Red Flag Warning. This general area looks to solidly exceed Red Flag criteria for several hours this afternoon (RH <25%, sustained winds 20+ mph and 10 hour fuel <9%), and is thus the region we are most concerned about for the spread of brush fires this afternoon.

Conditions farther east will not be much better. In fact, the first two criteria listed above for Red Flag conditions are likely to be meet this afternoon, but for a shorter duration then areas to the west. Additionally, the 10 hour fuel moisture threshold will be more difficult to obtain across far eastern IL into northwestern IN, owing to the wetting rain (~0.1") that has occurred overnight. It is for these reasons that we cut the eastward extent of the Red Flag Warning. We did issue a SPS (Special Weather Statement) east of the going Red Flag Warning to message the lower, but still heightened, fire threat.

Dewpoints are expected to tank into the 20s from west to east across northern IL late this morning and afternoon following the passage of frontal boundary/quasi-dry line. This will result in afternoon RH percentage values falling as low as 15-20% (lowest in the Red Flag Warning area) as temperatures warm into the mid to upper 60s. It is quiet rare to have RH values fall below 20% in this part of the country at any time of year, let alone in mid February. Unfortunately, these very dry conditions will be accompanied by strong gusty westerly winds (gusts of 35 to 45 mph) during peak heating this afternoon, making for elevated to Critical Fire Weather conditions. Accordingly, outdoor burning is not recommended, particularly in the Red Flag area.

KJB

LOT WATCHES/WARNINGS/ADVISORIES

IL...Red Flag Warning until 8 PM CST this evening for ILZ003-ILZ004- ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ014- ILZ019-ILZ020-ILZ021-ILZ022-ILZ023-ILZ032.

Wind Advisory until 6 PM CST this evening for ILZ003-ILZ004- ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ103- ILZ104.

IN...None. LM...Gale Warning until 6 PM CST this evening for the IL nearshore waters.

Small Craft Advisory until 6 PM CST this evening for the IN nearshore waters.