textproduct: Chicago

KEY MESSAGES

- Temperatures will tumble tonight into Friday. Some slushy snow accumulations (not likely on pavement) are possible mainly west of the Fox Valley Friday morning.

- Strong westerly winds develop late tonight south of I-80 then spread across the entire area through Friday morning. Wind Advisories in effect for gusts 45+ mph.

- Additional shots of snow late Saturday night into Monday, mainly near the lake in NW Indiana with some minor accumulations possible.

DISCUSSION

Issued at 225 PM CST Thu Feb 19 2026

Through Friday Night:

Latest objective analysis depicts a roughly 994 mb surface low just east of Kansas City. An attendant trough axis is steadily pushing northwestward across the area, with dewpoints surging into the 40s and lower 50s in its wake. The true system warm front appears to be farther south across downstate Illinois where temperatures are steadily warming into the mid/upper 60s. The aforementioned trough axis will continue to sharpen in the vicinity of the I-88 corridor this afternoon, as northeasterly flow strengthens off the lake.

An initial arc (or arcs) of isolated to scattered showers and thunderstorms may develop through the 4 to 6 PM timeframe as moist upglide increases. With widespread cloud cover limiting insolation, air temperatures are generally in the upper 50s/near 60 with dewpoints in the upper 40s and lower 50s. This will result in limited instability (MLCAPE of just a few hundred J/kg) given a lack of a deeper reservoir of cold air aloft. While deep layer shear is quite impressive, the combination of limited instability and lingering inhibition suggests the severe weather threat in the area should remain fairly low. Can't ever totally rule out some "funny business" in the vicinity of the area of enhanced low-level vorticity near the I-88 trough/front if a stronger updraft manages to get going, but the chances for this appear low. The more likely outcome is that any low-topped storms have a difficult time becoming surface based, with mainly a threat for small hail and locally stronger/gustier winds.

Later this evening (after 7-8 PM), an additional more strongly- forced area of convection is forecast to develop across central Illinois and pivot northeastward across our region through this evening/early overnight. This activity will occur within a narrow corridor of increased 0-3 KM MLCAPE, but without a mature/intense squall line or stronger supercell, the potential for surface based inflow appears fairly low based on the latest forecast soundings. As before, the main threats with any more robust activity looks to be from mainly small hail and gusty winds. Can't rule out a severe hailer or two in this regime, but the severe weather potentially generally appears a bit lower than it did yesterday.

The system dryslot will blast across the region late this evening and overnight, bringing a swift end to any lingering thunderstorm chances from southwest to northeast. Guidance continues to suggest the surface low will track across northwest Illinois. As this occurs, a brief period of low clouds, drizzle, and fog will be possible. Any brief locally dense fog threat should likely remain tied to the lake vicinity into far NE Illinois, and will erode quickly through daybreak with the arrival of the main cold front.

As the front arrives, expecting southwest to westerly winds to increase markedly as low-level lapse rates steepen and impressive pressure rises overspread the area (guidance suggests 12+ mb/6hr and about 5 mb/3hr) with the surface low deepening as it tracks overhead. Mean boundary layer flow is progged to increase to near 35 kts, with top-of-channel momentum transfer suggesting periodic gusts near 45 (possibly briefly over 50 mph) mph developing, initially south of I-80 late tonight before spreading across the rest of the area through Friday morning. Have issued Wind Advisories for the area to cover the strong and gusty wind threat. Winds will diminish steadily through Friday afternoon and evening.

Through Friday morning, the column will cool markedly as the surface low pulls northeast across the lake. A trailing mid- level deformation axis is forecast to push eastward across the area which will result in the redevelopment of stratiform precipitation, particularly west of the Fox Valley. As this develops, the atmospheric column will cool rapidly, supporting a transition to all snow prior to daybreak near I-39 and then closer to mid-late morning across NE Illinois. While ascent will be on a steady downward trend through the morning with the low pulling away, a brief burst of steadier snow is nonetheless possible west of the Fox Valley and particularly in the vicinity of I-39. Temperatures will likely be at or above freezing during this period, so unless snowfall rates get out of hand (which we're not seeing a strong signal for), any slushy accumulations (one half to maybe near an inch) would be relegated to grassy/elevated surfaces. Activity should tend to diminish in intensity with eastward extent through the morning, with a transition to intermittent light flurries during the afternoon.

Carlaw

Saturday through Thursday:

While the upper-level pattern will remain active on Saturday with numerous perturbations and broad (yet disorganized) cyclonic flow in place, the eastern fringes of a robust 1040 mb surface high will build into the region which looks to keep things generally quiet. A lingering tight pressure gradient will ensure northwesterly breezes remain in place leading to blustery conditions as winds gust into the 20-25 mph range with temperatures only warming into the mid to upper 30s.

A series of shortwaves embedded within the broad cyclonic flow will drop south out of Wisconsin and Michigan on Sunday and Sunday evening. In turn, mid and upper-level winds will turn northwesterly and colder air will spill southward. Some increase in boundary layer moisture, coincident with steepening lapse rates may support the development of some snow showers, primarily downwind of the lake into parts of northwest Indiana. With 850 mb temperatures forecast near -15 C, lake effect parameters don't appear overly significant, but sufficient to sustain accumulating snow showers with lake-induced ELs progged near 6-7 kft. Generally NNW to NW boundary layer flow looks to focus the bulk of this activity across parts of Porter County at this time. That said, there are some indications pointing to the flow veering more northerly Sunday night into Monday which could focus additional LES a bit farther westward.

A surface high will transit the region through Monday night with southwesterly return flow redeveloping on Tuesday. Strong/gusty south-southwest winds will start to push a warmer airmass overhead, although a lingering stout inversion will likely limit the degree of mixing we see Tuesday afternoon. Still, medium range guidance suggests we may mix deep enough to drive 30-40 mph gusts and temperatures warming into the low to maybe mid 40s across our far southwest (cooler towards the northeast). Noting that the ECMWF remains a bit warmer than the rest of the guidance suite, and has RHs falling to around 20 percent Tuesday afternoon. If this materializes, we'd have to keep an eye on another heightened grass fire threat, although the latest multi- model consensus suggests slightly cooler temperatures and higher humidity.

Active split flow pattern will continue through the middle/end of next week with the next chances for precipitation in the Wednesday/Thursday timeframe.

Carlaw

AVIATION /06Z TAFS THROUGH 12Z SATURDAY/

Issued at 1053 PM CST Thu Feb 19 2026

Forecast concerns include...

Possible brief ifr/lifr cigs/vis with dense fog next few hours. Strong/gusty west/southwest winds overnight then westerly Friday. Chance of snow showers Friday.

A few showers will be possible through the early overnight, but the bulk of any precipitation will be shifting north and east of the terminals soon. Thunder potential will also remain east and southeast of the terminals.

Surface low pressure will move across far northern IL during the overnight hours and there will be a brief period where fog, possibly dense fog may develop, mainly in the 07z to 09z timeframe. Confidence is low, but if it happens, it likely will be ifr/lifr vis and opted to include a short tempo for this potential, which will end as winds shift to the southwest.

Easterly winds to start will turn southeasterly in the next few hours, then southerly, then shift southwest and steadily increase with gusts into the lower/mid 30kt range. Gusts may peak just after daybreak and then are expected to slowly diminish through Friday afternoon then diminish further Friday evening.

There remains a chance of snow Friday morning, especially at RFD, but confidence remains low for how much snow may make it to the Chicago area terminals. Opted to shift the prob mention more into the morning hours for the Chicago terminals and maintained prevailing snow at RFD. But trends will need to be monitored through the night. cms

LOT WATCHES/WARNINGS/ADVISORIES

IL...Wind Advisory from 6 AM to 4 PM CST Friday for ILZ003-ILZ004- ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ103- ILZ104.

Wind Advisory until 4 PM CST Friday for ILZ019-ILZ020-ILZ021- ILZ023-ILZ032-ILZ033-ILZ039-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Wind Advisory from 6 AM CST /7 AM EST/ to 4 PM CST /5 PM EST/ Friday for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory until 6 AM CST Friday for Winthrop Harbor to Northerly Is. IL.

Gale Warning from 6 AM to 6 PM CST Friday for Winthrop Harbor to Northerly Is. IL.

Gale Warning from 2 AM to 6 PM CST Friday for Northerly Is. IL to Michigan City IN.