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KEY MESSAGES

- The heavy lake effect snow will remain east of Porter County this morning, with periods of lighter snow and lingering hazardous travel. The Winter Storm Warning has been canceled and replaced with a Winter Weather Advisory, in effect until 10 AM CST.

- Accumulating snow is expected tonight, likely resulting in hazardous travel conditions.

- Thursday night system will be just one of many clipper-like systems riding the northwest flow across the region bringing occasional chances for snow, each followed by very cold and windy conditions. Bitterly cold conditions are possible Sunday night through early Tuesday.

UPDATE

Issued at 705 AM CST Thu Jan 15 2026

Downgraded the Winter Storm Warning for Porter County to an Advisory for lingering hazardous travel. It's become clear based on observations that the heavier band farther east will no longer be able to push back west as far as the Porter-LaPorte line. Instead of simply canceling the warning, opted to replace it with an advisory, as there is still lighter multi-cellular lake effect snow streaming into northern portions of the county. With the heavy band no longer a threat to reach eastern Porter, this subsequently ended the chance for accumulating snow into northeastern Jasper, and as such, canceled the advisory there.

Castro

DISCUSSION

Issued at 358 AM CST Thu Jan 15 2026

Through Friday:

Porter County Lake Effect Snow This Morning:

The lake effect snow overnight has been a stream of multi- cellular/mult-banded light to occasionally moderate snow. We're closely monitoring the anticipated westward progression of the intense band that has been impacting southwest Lower Michigan and interior northern Indiana. The HRRR and RAP (and 00z WRF-ARW last night have depicted the most aggressively far west shift of the intense band. These models have been a generally better observational match for winds across western Lower Michigan, vs. farther east guidance such as the NAM and NAMnest. It appears the clearing and colder conditions from Muskegon to Benton Harbor have been key in terms of aiding a westward shift in the lake induced convergence axis.

With the above being said, there has been a recent slight run to run shift back a bit east with the depiction of the band on the HRRR (to a lesser extent with the RAP). This will be essentially a nowcast situation with respect to intense snowfall rates (up to 2-3"/hour) and higher end (dangerous) travel impacts reaching into northeastern Porter County or staying just east of the Porter-LaPorte line. With the slower westward progress of the band to this point and heaviest snow not occurring until after 6 AM then finally shifting east 10-11 AM, opted to proactively extend the Winter Storm Warning to noon today. Should the heavier snow fail to push into northeastern Porter, we'll be able to cancel the warning early. Anticipate significant variability over short distances common in lake effect snow.

Castro

This afternoon through Friday:

Focus during the remainder of the short term forecast period is on the potential for accumulating snow tonight into early Friday, in association with a digging short- wave currently cross the Canadian Rockies. Strong low- level warm advection and associated isentropic ascent develops into the region this afternoon ahead of the approaching wave. Increasing ascent/cooling leads to mid-level saturation developing across far north/northwest IL prior to sunset, and while dry low-levels will take a little longer to moisten, light snow or flurries may develop as early as 4-5 pm. Strongest forcing and deep saturation appears focused on the evening hours, with a few hour period of accumulating snow through midnight or so (a little later farther east into northwest IN). Noted in recent guidance however, is a trend toward mid-level drying and even potentially the loss of ice nuclei behind the warm advection wing for a time after midnight to varying degrees between various models. This would appear to limit the duration of better snow accumulation to the evening hours with a transition to poor quality/lower SLRs overnight, or in some guidance even potentially a change over to freezing drizzle for a time. Needless to say this lowers confidence in snow amounts (generally around an inch most areas with current guidance). Have not included any freezing drizzle mention at this time with inconsistencies in guidance, but this will need to be assessed further today with new model data.

Moisture depth does increase Friday morning as the main vort rotates overhead, though there remains spread in guidance even at 30 hours out in just long it persists. Continued cooling of the column and steepening of lapse rates does look to support a period of snow or snow showers during the day Friday with some additional accumulation potential especially during the morning, after which the mid-level vort axis moves east.

Temperatures will remain below average today in the wake of Wednesday's cold front, generally in the mid-20s by this afternoon. Temperatures should slowly rise tonight after a brief evening dip as breezy south-southwest winds develop. Friday looks to be the mildest of the next several days, with highs warming above freezing in the mid-30s.

Ratzer

Friday Night through Wednesday:

In the wake of the next Arctic front passage Friday evening, snow showers and/or flurries will be possible really at any time through Saturday evening as the column is progged to be firmly within the DGZ. This looks like a "leaky stratus" setup, with passing short-wave impulses invigorating snow shower activity, but also lending lower predictability to where and when accumulations may cause some travel impacts (considering the well below freezing temps). Temperatures may end up flatlining at best on Saturday with blustery westerly winds keeping wind chills in the -5 to +5 range.

Signs are pointing to a short break overnight Saturday night into Sunday with breezy southwesterly "warm" advection in advance of the next Arctic front crossing the area Sunday evening and night. This could have snow showers or flurries ahead of and in the wake of the Arctic front late in the day into the evening. Strong northwest winds later Sunday night into Monday could result in patchy blowing snow in open areas (dependent upon sufficient snow cover).

Ensemble support increased in the 00z cycle for a dump of bitterly cold air following the Sunday night Arctic fro-pa. Cold weather headlines are a distinct possibility Sunday night-Monday AM through Monday night/early Tuesday prior to the next brief moderation in temps midweek next week.

Castro

AVIATION /12Z TAFS THROUGH 18Z FRIDAY/

Issued at 604 AM CST Thu Jan 15 2026

Main Concern:

- Periods of accumulating snow this evening into Friday morning adding up to around 1", accompanied by MVFR to occasional IFR flight categories. Highest confidence timeframe is late evening-early overnight.

Flying conditions will be much quieter during the daytime hours today. MVFR CIGs and intermittent flurries from ORD and MDW to GYY should finally clear out this morning, with gusty northwesterly winds also easing.

Winds will become southwesterly this afternoon in advance of the next system as mid-level clouds thicken. Confidence has decreased in dry air being sufficiently eroded to enable snow to reach the ground in the late afternoon and early evening. Opted to hold onto TEMPO mention for 5-6SM flurries. Accumulations are not expected with the initial snow.

There is some uncertainty for the exact onset time of accumulating snow this evening (02-04z in the TAFs). After onset, expect a 2-3 hour period where IFR VSBY snow is probable. Following a lull, another disturbance moving over the area in the pre-dawn through just after sunrise Friday timeframe could produce a short burst of IFR VSBY snow (1-3 hours), covered with a PROB30 for now in the TAFs. Southwest winds will gust up to 20-25 kt at times late this evening through Friday morning.

Castro

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...Winter Weather Advisory until 10 AM CST this morning for INZ002.

LM...Small Craft Advisory until 3 PM CST this afternoon for Winthrop Harbor IL to Gary IN.

Small Craft Advisory until 6 PM CST this evening for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.