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KEY MESSAGES

- Turning sharply colder today behind a strong cold front early this morning with northerly winds gusting up to 30-40 mph.

- Wind-whipped snow showers likely this morning near and east of I-39, with lake enhancement commencing into northwest Indiana.

- Winter Weather Advisory remains in effect for northern and eastern Porter County for lake effect snow showers today and tonight, localized accumulations of 2-5 inches expected, especially northeast Porter County.

- A "Clipper Express" pattern may materialize from the end of this week into early next week with periodic opportunities for snow, reinforcing shots of cold air, and blustery northwest winds.

DISCUSSION

Issued at 345 AM CST Wed Jan 14 2026

Through Thursday:

Temperatures have been running a few to several degrees milder to this point than previously expected, but this will change quickly as a strong cold front (over southern Wisconsin as of this writing) sweeps southeastward across the area.

A potent vort lobe packing very cold mid-level temps can be seen nicely on water vapor imagery this morning across north central Wisconsin. It appears that the large scale forcing from the vort lobe, along with sufficient frontal forcing, and sufficiently deep convective cloud depths has been enough for a fairly well organized area of snow showers extending across central Wisconsin. These snow showers will push southward across areas near and east of I-39 towards and after daybreak.

Bumped up PoPs to account for radar trends, and recent guidance trends getting a much better handle on the snow showers this morning. It doesn't appear to be a high end snow squall scenario, though we'll need to watch for embedded "squall-like" behavior with brief very low visibility and gusts perhaps a bit higher than the already strong background wind fields expected this morning. Air and pavement temps running above freezing through the night may tend to limit pavement accumulations unless under a more intense burst of snow. A bit more concern in this regard for areas east of I-57 and particularly downwind of Lake Michigan in northwest Indiana. A coating to locally a half inch may occur on colder surfaces east of I-39 in Illinois, with locally 1/2 inch to 1" in northwest Indiana, particularly in Porter County due to north-northwesterly flow from the lake.

Also have been noting potential for some additional snow showers to develop into northeastern and east central Illinois later this morning in the strengthening cold air advection regime. This may be tied to better deep layer moisture pivoting southward catching up to the still strong large scale forcing. All in all, any robust snow shower activity (outside of lake effect snow in northwest Indiana), should be confined to primarily this morning, ending early this afternoon near and east of I-57 in eastern Illinois into Indiana well south of the Kankakee River.

If temperatures fall quickly enough coincident with still falling precipitation, there may be some potential for localized "flash freeze" conditions, but it's unclear how this will play out. We'll continue to monitor upstream observations, webcams, and road conditions and may consider a Special Weather Statement if warranted, in tandem with graphical messaging.

Temperatures will be in the low-mid 20s for most of the area during the afternoon hours with north-northwesterly winds continuing to gust up to 30-40 mph, strongest near the lake, resulting in wind chills in the single digits for the evening commute.

Castro

Regarding the lake effect snow...

There are no big changes in forecast thinking, with the Winter Weather Advisory for Porter County starting at 8 AM and ending Thursday morning. Will push out the advisory end time to 9 AM Thursday, as light snow and blowing snow should extend into the Thursday morning commute for northeastern sections of the county.

Meteorologically, strong cold air advection over a fairly warm lake (SSTs in the lower 40s over most of the open waters) should result in moderately strong lake induced instability Wednesday into Wednesday night. Inversion heights are progged to be extreme, topping out 6-8kft, but plenty high to support some heavy lake effect snow showers, particularly given the DGZ embedded within the convective clouds.

Expecting mostly multi-banded lake effect set-up during the daytime hours Wednesday, effecting northern and perhaps eastern Porter County. Wednesday night, land breeze convergence could lead to a more dominant, strong lake effect band, which would likely take aim on areas east of Porter County. Some of the CAM guidance suggests the there could be a weaker secondary band to the west over Porter County or even just some weaker multi-band structure snow showers. Lake effect chances for Porter County look to decrease after sunrise Thursday morning as winds back and push the band east into WFO IWX's area. Given the strong winds (at least minor blowing and drifting snow) and the potential for 2-5" of snow, hazardous travel can be expected. As is typically the case with lake effect, totals could vary significantly over a short distance.

The rest of Thursday will be the temporary break before accumulating snow arrives Thursday night, detailed in the next section below. Highs will reach the mid to upper 20s.

Izzi/Castro

Thursday Night through Tuesday:

Global model guidance remains in good agreement in maintaining a highly amplified upper level pattern, featuring a deep long- wave trough across eastern North America, into early next week. Several digging short waves are noted in EPS/GEFS and GEPS ensembles through the period, with the first arriving Thursday night. Spread decreases however, with the timing and track of later successive disturbances. Overall, the pattern appears to favor the potential for some accumulating snow Thursday night into Friday with a bit a warm-up, followed by colder and occasionally blustery weather punctuated by occasional periods of snow/snow showers/flurries through the remainder of the forecast period.

A mid-level short wave was evident in upper air data and GOES vapor imagery off the British Columbia coast early this morning, associated with a 150 kt upper level jet streak. This feature is progged to cross the Canadian Rockies later tonight, then dig southeast and amplify across the upper Midwest Thursday. Increasing forcing for ascent develops ahead of the approaching wave late Thursday/Thursday evening, resulting in top-down saturation and the likely development of snow from west to east across the area during the evening as a modest (~1004 mb) surface wave develops along an occluding Pacific frontal trough. Strongest forcing appears to persist through shortly after daybreak Friday when the initial short wave vort and trough axis passes. There are some lingering spatial differences in the model QPF output with this wave, though with general agreement in amounts around 0.15" liquid and Cobb snow/liquid ratios in the 12-15:1 range. This would appear to support a snowfall in the 1-3" or 2-3"range across the forecast area, though the location of the higher amounts is of low confidence just yet.

While deep, synoptic ascent eases with the passage of the initial wave Friday morning, continued deepening/amplification of the upper level trough and associated cooling of mid-levels looks to result in an increasingly deep layer of steepening low-level rates Friday afternoon into Friday night. This will likely support some additional snow showers or even snow squalls as winds ramp up in response to deepening surface low pressure over the northern Lakes. Models remain in good agreement in depicting a reinforcing push of much colder air arriving later Friday night.

As noted above, the upper level trough is then forecast to linger across the region through the weekend and into early next week. Ensembles depict several additional digging short waves which may bring some additional snow/snow shower chances during the period, though model spread in the timing and track of these remains and lowers confidence in adding forecast detail with respect to these at this time. There is good agreement however that the push of colder arctic air that arrives Friday night will persist through the remainder of the period. Nighttime lows in the single digits and daytime highs in the upper teens to near 20 appear in store through the weekend and into early next week. Wind chills look to remain in the single digits either side of zero, along with occasional chances of additional snow showers and flurries.

Ratzer

AVIATION /06Z TAFS THROUGH 12Z THURSDAY/

Issued at 1051 PM CST Tue Jan 13 2026

Wind shift to north/northwest in the predawn hours. Strong/gusty north/northwest winds Wednesday. Scattered snow showers Wednesday morning.

A cold front will move across the terminals in the predawn hours, shifting west/northwest winds to north/northwest with gusts increasing into the lower 30kt range, which will continue through mid morning and then diminish a bit into the mid/upper 20kt range midday. Gusts are expected to diminish further into the lower 20kt range Wednesday evening.

Scattered snow showers are expected behind the cold front. These snow showers may only last 2-3 hours and there is still uncertainty for coverage, but latest guidance supports moving to tempo mention, which is also an hour later based on current trends for the cold front. Brief ifr vis and possibly brief ifr cigs will be possible with these snow showers. There may also be some blowing snow. Once these snow showers move southeast of the terminals, there may be passing flurries into the afternoon.

Prevailing mvfr cigs are possible behind the cold front through mid morning before lifting back into low vfr. Opted to include a prevailing mvfr cig during this time, but only medium confidence. cms

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...Winter Weather Advisory from 8 AM this morning to 9 AM CST Thursday for INZ002.

LM...Gale Warning until 9 PM CST this evening for Winthrop Harbor IL to Gary IN.

Gale Warning until 3 AM CST Thursday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.