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KEY MESSAGES

- Lake effect rain showers will continue into the day Saturday before ending Saturday afternoon. Showers may mix with or briefly change to wet snow overnight with little to no accumulation expected.

- Seasonably cool temperatures are expected through the weekend with a gradual warming trend back to above average by the middle and end of next week.

UPDATE

Issued at 813 PM CST Fri Nov 13 2026

The inherited forecast appears to be in excellent shape.

A steady stream of lake effect showers continues to push into northwestern Indiana this evening within an impressively persistent convergence axis arcing down the spine of Lake Michigan. While there has been a westward drift to the showers this evening (a response to one last upper-level shortwave pinwheeling overhead), the convergence axis is once again well east of basically all guidance. So, did opt to gently nudge PoPs a tad eastward through the overnight hours to be more closely aligned with the current position of the band.

Similar to last night, temperatures beneath the band of lake effect showers/stratus are running several degrees warmer than model guidance. While temperatures should slightly cool with time overnight, can still envision snow mixing with rain at times (particularly on the fringes of the band where wet bulb cooling will be most efficient). Provided precipitation type does include or change entirely to snow at times, marginal air and ground temperatures should prevent snow accumulations outside a dusting on elevated surfaces.

The only other item of note is the ongoing Flood Advisory in far southeastern Cook and central Lake (IN) counties beneath the band of lake effect showers. With 48 hour MRMS rainfall measurements ranging from 1.5 to locally 2.5 inches (highest totals near Lake Michigan shoreline) and fall leaves likely lining streets and sewers, do suspect there area areas of ponding and nuisance-type flooding in typical flood prone locations. So, will continue the Flood Advisory through the overnight hours. (It is fairly unusual that a lake effect event is defined by over 2 inches of liquid equivalent precipitation in our area).

Updated grids have been sent.

Borchardt

DISCUSSION

Issued at 123 PM CST Fri Nov 13 2026

Single band of lake effect showers stretches down the full length of Lake Michigan early this afternoon. Showers in our area have been largely confined to northwest Indiana. After some wet snow mixed in with the rain showers this morning over portions of Lake County Indiana, precipitation has transitioned to all rain. No accumulations were reported to our office, though on webcams we did see some brief slushy accumulations appearing to be less than an inch on grassy and elevated surfaces this morning before it quickly melted.

Water vapor imagery early this afternoon depicts one last well defined shortwave trough and associated vort max over eastern WI. This trough axis will move south of the Lake by early this evening which should result in lowering inversion heights tonight and Saturday. Inversion heights this evening should remain favorable for a formidable lake effect band. High resolution guidance does suggest that this band could wobble back west into northeast IL this evening, likely in response to a bit of a mesolow developing over the lake. The weakening boundary layer flow should promote a strong land breeze this evening and give still favorable instability, certainly plausible that a meso-low could form. If a meso-low doesn't form, then lake effect should remain targeted on northwest Indiana this evening and regardless of meso-low development or no meso-low the lake effect should gradually shift eastward overnight into Saturday morning focusing more into Porter County and eventually east of our CWA Saturday.

The lowering inversion heights, less favorable stability profiles over land, and weakening onshore boundary layer flow would all suggest this lake effect band should struggle to penetrate as far inland later this evening and especially overnight into Saturday. Thermodynamic profiles would potentially support some wet snow mixing in this evening, given sufficient inland penetration, but with sfc temps likely just above freezing, even if the band were to penetrate far enough inland where the air mass would be cold enough for snow, accumulations would be unlikely. Overnight the lesser inland penetration should reduce snow chances, as too will the inversion heights which should drop below the -10C level, leaving lake effect convection lacking the ice nuclei needed for snow.

Outside of the lack effect tomorrow, the remainder of the area will become sunny. Mostly sunny skies are then expected through the first half of the upcoming work week. Temperatures this weekend will be near average (though given the unseasonable warmth of late, will likely feel pretty cool). Generally dry weather is expected for the upcoming work week with highs warming back into the 50s and possibly into the 60s by the end of the week. Normal highs are in the 40s this weekend through next week.

- Izzi

AVIATION /00Z TAFS THROUGH 06Z SUNDAY/

Issued at 536 PM CST Fri Nov 13 2026

Only aviation forecast concern tonight is how far west the current lake-effect precipitation band shifts (or doesn't) for potential MDW/ORD impacts.

Current regional radar depicts a north-south oriented band of lake-induced precipitation focused into northwest IN, focused toward and east of KGYY. KGYY is situated such that the western periphery of this band will likely continue to impact it overnight, before eventually drifting east by mid-morning Saturday. Surface temps in the low-40s and wet-bulb temps above freezing should continue to support rain as the primary precipitation type this evening, though high-res model forecast soundings indicate there may be a period during the overnight hours where some wet snow flakes could mix in with the rain.

There remains decent agreement in high-res guidance (HRRR, time-lagged HRRR and RRFS) that the band may shift further west toward northeast IL in the 04-10Z period, though guidance has generally been too far west with these indications over the past 24 hours or so, thus confidence is fairly low in direct impacts to KORD/KMDW. Have maintained the inherited VCSH/PROB30 mentions for these sites, but moved them back a few hours per above mentioned guidance trends. Passage of a mid-level wave after midnight should eventually end this threat for northeast IL sites.

Other than periodic MVFR conditions with the lake-effect showers at GYY into Saturday morning, VFR conditions are otherwise expected. Winds will gradually ease with time, but generally remain NNW through the period.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 6 PM CST Saturday for Winthrop Harbor IL to Gary IN.

Small Craft Advisory until midnight CST Saturday night for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.