FXUS63 KIWX 130002

AFDIWX



Area Forecast Discussion

National Weather Service Northern Indiana

702 PM EST Fri Dec 12 2025



.KEY MESSAGES...



- Lake effect snow showers tonight, primarily for Berrien

  County. Accumulations of less than one inch.



- Light snow Saturday afternoon (accumulations 1 to 3 inches),

  transitioning to lake effect snow showers Saturday night into

  Sunday (additional 2-4").



- Wind chills of -15 or colder Saturday night and Sunday night.



&&



.DISCUSSION...

Issued at 228 PM EST Fri Dec 12 2025



Primary topics of interest this afternoon are 1) incoming clipper 

system Saturday afternoon and night (snow duration ~6 hours), 

followed by lake effect snow, and 2) below-zero wind chills Saturday 

night and Sunday night.



A compact but strengthening upper-level disturbance races across the 

northern Rockies this afternoon, arriving on our doorstep Saturday 

afternoon just as an upper-level low drops due south from Ontario. 

This results in a strengthening area of frontogenesis across central 

Indiana. Forecast soundings depict a shallow dry layer saturating 

quickly amid this highly-forced environment and a deepening 

Dendritic Growth Zone through time (approaching 500mb after 21z/4PM 

EST). Given the continental polar source region of this air mass, 

snow ratios will be high (+/-15:1) resulting in efficient 

accumulation despite the brief residence time. Snow amounts of 2" to 

3" are expected south of US 24 while most of the forecast area will 

see 1-2" from this clipper. The exception will be south-central 

Michigan which will generally miss both the clipper and subsequent 

lake effect. Wind from the northwest near 10 mph Saturday will 

result in some blowing and drifting. Wind gusts near 20mph will be 

confined to those downwind of lake Michigan. Synoptic ("system") 

snow ends before midnight. An advisory was considered for my far 

southern Indiana Counties, but seeing such low-end advisory amounts 

amid an above-average snow season so far made me less enthused for 

headlines. The incoming shift may update as needed, especially if 

the storm track shifts north. 



In the wake of this clipper, lake effect snow develops Saturday 

evening and persists through Sunday. This is preceded by a brief 

period of lake effect snow tonight, primarily for Berrien County and 

those along the toll road. Equilibrium levels are shallow (< 5k FT) 

with an elevated and poorly saturated DGZ. Thus, amounts by daybreak 

Saturday will be less than 1". Given this < 1" accumulation for 

tonight, opted to delay any headline issuance for the time being.

For lake effect snow Saturday afternoon through Sunday, accumulation 

will favor Berrien, Cass (MI) La Porte, and St. Joseph (IN) 

Counties. Lake effect parameters will be most favorable Saturday 

night / early Sunday morning.



Outside of the lake effect snow, temperatures will plummet Saturday 

night as skies clear and Canadian high pressure becomes established 

over the Ohio Valley. Those near White and Cass (IN) Counties will 

see lows below zero while the remainder of the forecast area will 

see single-digit lows. Being at the mercy of decreasing clouds, this 

decreases forecast confidence for the issuance of any Cold Weather 

Advisories at this time. Sunday night, with lake effect clouds 

decreasing, all areas are expected to be on either side of 0. Wind 

chills of -15 to -20 may warrant a Cold Weather Advisory. 



Thawing out Tuesday through Thursday as upper-level ridging moves 

in. Highs will creep into the 40s Wednesday and Thursday. Low 

pressure moves through the Upper Midwest late in the week bringing 

renewed chances for rain and snow.



&&



.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...

Issued at 654 PM EST Fri Dec 12 2025



MVFR cigs for both TAF sites expected through the remainder of 

this forecast period with MVFR to IFR category vsbys in light snow

after 16z Sat as a disturbance pushes through the area with

heavier snowfall expected south of both terminals primarily

central IN as the better deformation band sets up in this

location. The southerly track of this system would also put KFWA

with the better chances of the lowered vsbys and heavier bursts

of snowfall compared to the further north KSBN terminal.  



&&



.IWX WATCHES/WARNINGS/ADVISORIES...

IN...None.

OH...None.

MI...None.

MARINE...Small Craft Advisory from 10 PM this evening to 10 PM EST 

     Sunday for LMZ043-046.



&&



$$



DISCUSSION...Brown

AVIATION...Andersen