Marine Weather and Tide Forecast for Winthrop Harbor, IL

DISCUSSION
Issued at 241 PM CST Sat Jan 24 2026

Through Sunday night:

Forecast on track with no meaningful changes to previous forecast for the approaching winter storm. I am concerned that lake effect snow could overperform a bit very late tonight into Sunday morning over northeast IL and into northern Lake Co Indiana Sunday afternoon, but confidence is a bit too low to justify an upgrade to a winter storm warning at this time.

Large winter storm is slowly approaching the area this afternoon though very dry antecedent air mass is taking some time to saturate from top down. WSR-88D imagery does suggests that the low level dry air is being eroded and expect areas of light snow and flurries to begin making it to the surface soon.
Light snow will likely continue tonight, especially south of I-80.

Most of the ascent tonight appears to be the result of upper level divergence in the right entrance region of developing upper level jet streak over the western Great Lakes. As such, strongest upward vertical velocities (UVVs) are progged to be above 600 mb, well above the very deep DGZ where weak UVVs are progged to be neutral or even weak subsidence. This suggests that predominant snow type for most of tonight will be smaller flake size and resultant lower snow:liquid ratio (SLR). Nudged the forecast SLR down some, but possibly still too high if the snow tonight is mostly pixie dust and low SLR. Confidence wasn't high enough to make any big adjustments to snowfall totals, but that is something the evening shift will need to look at for the first half of the event tonight.

By early Sunday morning, we start to get into an area of coupled jets with some strengthening mid-level frontogenesis. This could result in a period of stronger UVVs below 600mb and closer to the DGZ. This may produce heavier snowfall rates Sunday morning where larger dendrites result in higher SLRs, at least in mesoscale band(s). The system snow should end from west to east from mid afternoon Sunday through early evening.

One wildcard will be the lake enhanced snow late tonight into Sunday. While there will be a strong frontal inversion between 800-850mb through the duration of the event, limiting the depth of the lake induced convective instability. While the depth of the instability looks to be rather shallow, the instability below the inversion will be quite strong with lake-850mb delta T values around 20C. This should result in very strong ascent below the inversion, the majority of which will be smack dab in the middle of the DGZ. I am concerned that seeder-feeder process from strong synoptic ascent above 600mb could result in a band of intense lake effect snow embedded within an area of lighter snow and flurries. Wouldn't be surprised to see snowfall rates >=1" per hour with the lake enhanced snow Sunday morning into NE IL, gradually shifting into NW IN Sunday afternoon. Certainly a play for totals solidly over 6" into northeast IL if the lake enhancement really gets going, but confidence isn't high enough to justify an upgrade to a warning at this time. Will be something that later shifts will need to closely watch.

Intensity of the lake effect should begin to decrease Sunday evening as it loses seeder-feeder with synoptic snows shifting east of the area. Inversion heights are progged to come up a bit Sunday evening, so did maintain likely pops for LES across northeast IN Sunday evening. By late Sunday evening the LES threat should push east of Porter County, so the midnight expiration time for the winter weather advisory looks good for Lake/Porter Counties.

- Izzi

Monday through Saturday:

No significant changes to extended thinking at this time.

Following the weekend system, an energetic and active upper pattern will remain in place with fast, northwesterly flow aloft likely to guide additional disturbances across the Upper Midwest and Great Lakes region through the week. Regarding late Sunday night/Monday morning: latest guidance suggest we may need some additional cold weather headlines during this period to start the week with wind chills possibly nearing 20 below range. Given that this is marginal/borderline advisory criteria, we're holding off on a wind chill advisory at this time and will let subsequent shifts re-assess.

Latest indications point to generally precip-free conditions on Monday as fairly robust mid-level height rises spread in from the west through the afternoon. The nose of a ~130 kt jet streak will impinge on the region late in the day, but at this time only looks like it'll drag some increasing mid and high-level cloud cover overhead. Northwest to west-southwest breezes with a lingering fairly tight surface pressure gradient will hold wind chills largely below zero through the day.

On Monday night, a fast-moving and fairly robust disturbance is slated to press southward out of the Minnesota Arrowhead Region and across the Great Lakes. Latest guidance currently takes the bulk of the most intense large scale forcing with this system to our north, and will continue with a dry forecast in our area as a result. The associated surface low will eventually drag a reinforcing cold front through the area on Tuesday which will send air temperatures back down to around 0 degrees Tuesday night with colder wind chills. In the wake of the front, forecast soundings look a bit more supportive of some intermittent flurries as lobes of strong shear vorticity meander southward through the afternoon and evening with increased saturation in a thin layer at the base of a deep DGZ. Good agreement that the boundary layer flow will remain westerly enough to keep an follow-up LES to our east.

Another, potentially even more intense shortwave is forecast to drop more solidly across our area on Wednesday and Wednesday night. Guidance generally appears supportive of a period of light snow somewhere in the vicinity, although noting a fair amount of north- south spread in the current deterministic and ensemble output. At this point, didn't see any reason to stray from the NBM-delivered chance PoPs during this period. Where snow does fall, very cold temperatures in the single digits and teens will once again lead to travel impacts.

Beyond this time, forecast confidence breaks down a bit, but there's an interesting signal of a fast-moving vort lobe backing southwest across lower Michigan sometime during the Thursday- Friday timeframe. This could potentially restart the LES potential in our area, but confidence is pretty low in specifics at this time.

Carlaw/Ratzer

AVIATION /18Z TAFS THROUGH 00Z MONDAY/
Issued at 1221 PM CST Sat Jan 24 2026

Forecast concerns for the terminals...

- Snow will spread into the area this evening resulting in a period of IFR visibilities overnight.

- A band of lake effect snow is expected to develop early Sunday morning and result in IFR to LIFR visibilities at the Chicago terminals and GYY.

The arctic high that brought us the bitter cold the past couple days continues to drift eastward over MI as a storm system begins to organize over the southern Plains. The lingering influence of the high will continue to promote VFR conditions and light northerly winds through this afternoon. Though, wind directions will become more northeasterly later this afternoon and evening as the aforementioned storm system approaches. While mostly dry conditions are expected through this afternoon, a few flurries cannot be ruled out as mid-level moisture increases.
Furthermore, there is also a band of lake effect snow just off shore of GYY which has a band of MVFR clouds associated with it.
So far any snow with these MVFR clouds has been flurries, but the concern is growing that as the aforementioned mid-level moisture increases that it may generate more robust snow showers from these clouds. Given that this is lower confidence have opted to just maintain a 6SM flurry mention at the Chicago area terminals for now.

Heading into this evening, the main snow shield with the aforementioned storm system will begin to spread into northern IL and northwest IN between 02z and 04z. As the snow arrives visibilities should diminish into the IFR (1-2SM) range shortly after snow begins. While the snow itself will persist through the night, it appears that the better forcing may drift east of the area after 07z which may allow for some improvement in visibilities into Sunday morning. However, a band of lake effect snow is expected to develop early Sunday morning and begin to move over the Chicago terminals and eventually GYY. Given the decent lake induced instability the lake effect band should be able to produce a period of 0.5-1" per hour snow rates which will result in IFR to LIFR visibilities at ORD, MDW, and GYY under the band. Additionally, winds under the band may also become breezy with northerly gusts around 20 kts.

Confidence on the lake effect band occurring remains high, but confidence on how long it persists over the terminals is much lower. For now have opted to capture the potential for the lowest LIFR visibilities in a PROB30 between 13z and 18-19z when guidance has a general consensus of the band being over the terminals. However, will maintain a longer period of IFR visibilities through Sunday afternoon to account for a slower band progression. Regardless of what the lake effect band does, the cold surface temperatures will result in at least 2-4 inches of accumulation (locally higher where the lake effect band goes) across much of northeast IL and northwest IN. Though, lighter snow amounts are expected near RFD (accumulations around a couple tenths to locally 1 inch).

Outside of the snow, expect MVFR conditions overnight to improve to VFR once the snow concludes. Winds will gradually become more northwest on Sunday with speeds remaining in the 5-10 kt range.

Yack

HYDROLOGY
Issued at 230 PM CST Fri Jan 23 2026

River gauges, reports from local officials, and reports from trained ice spotters continue to indicate a few ice jams across the area due to the significant increase in river ice over recent days. With continued cold weather into next week, conditions will remain favorable for river ice formation. While no widespread flooding is expected, localized ice jams may occur.

- NWS Chicago

LOT WATCHES/WARNINGS/ADVISORIES
IL...Winter Weather Advisory from 6 PM this evening to 6 PM CST Sunday for ILZ006-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023- ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107- ILZ108.

IN...Winter Weather Advisory from 6 PM this evening to midnight CST Sunday night for INZ001-INZ002.

Winter Weather Advisory from 6 PM CST /7 PM EST/ this evening to 9 PM CST /10 PM EST/ Sunday for INZ010-INZ011-INZ019.

LM...Small Craft Advisory from 9 AM Sunday to 6 PM CST Monday for Winthrop Harbor IL to Gary IN.

Small Craft Advisory from noon Sunday to 6 PM CST Monday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.