935
FXUS63 KIWX 081114
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
614 AM EST Sat Nov 8 2025

.KEY MESSAGES...

- Rain will spread across the area tonight and mix with snow by
  early Sunday morning. 1-2" is possible on grassy/elevated
  surfaces through Sunday morning.

- Lake effect rain and snow on Sunday will transition to all
  snow Sunday night. Heavy lake effect snow is possible near
  Lake Michigan Sunday night through Monday.

- 6-12" of snow with locally higher amounts is likely near the
  lake but confidence in the exact location is still low at this
  point.

- Winds from the north-northwest will gust up to 20 mph
  Sunday night into Monday and may cause some blowing and
  drifting in areas that see a lot of snow.

&&

.DISCUSSION...
Issued at 422 AM EST Sat Nov 8 2025

...Significant lake effect snow possible Sunday night into
Monday...

Very active weather is anticipated over the next few days with
multiple chances for the first snowflakes of the season.

Phase #1 Synoptic (System) Snow...

Potent midlevel circulation seen very clearly on morning water vapor
imagery over Montana will continue to dig SE into the Ohio Valley
tonight through Sunday. Good midlevel CVA and some left exit
(becoming coupled) upper jet dynamics will support modest surface
cyclogenesis over our region and into the Lower Great Lakes...
eventually pulling some colder air into the area. 925-850mb fgen
lights up over our area early overnight and grows in intensity and
depth by late overnight as the upper jet and surface low strengthen.
Widespread precip is expected overnight into Sunday morning. There
is however still some spread in the exact low track (southern IN vs.
central IN) which will impact where the heaviest precip sets up and
subsequently dictates the snow chances. Boundary layer temps are
initially too warm for snow and only become marginally supportive by
early Sun morning. This is where exact track of heaviest rates will
be key because the heavy rates will be needed to overcome surface
air and ground temps above freezing. Lower resolution models are
showing a more southern track while most of the hi-res guidance is
further north (to varying degrees). Prefer a middle of the road
approach here which supports of band of moderate snow roughly just
north of US-24. Here...heavy precip rates from roughly 09-15Z will
support a changeover to snow. (Further north, rates are lower and
further south, temps are warmer.) Accumulation efficiency will be
severely hampered by warm ground and surface temps 32-34F but a
quick inch or two on grassy/elevated surface is possible in this
"sweet spot". Will continue to fine-tune exactly where the best
combo of cold air and heavy precip rates sets up.

Phase #2.a Initial Lake Effect Sunday During the Day...

Behind the departing surface low, northerly winds down the long axes
of Lakes Superior and Michigan will light up a single, dominant lake
effect band by 12-15Z. 850mb temps around -8C to start the day will
drop to around -12C by late afternoon. Inversion heights are around
8-10 kft but there is some dry air near the surface that limits lake-
induced instability. The biggest negative factor for snow will be
temps in the mid/upper 30s during the day. With warm ground/pavement
temps it will be difficult for snow to accumulate. An intense LES
band could develop that is capable of overcoming the warm ground but
flow trajectories also back to NW by the afternoon which will
disrupt the single band and keep it from hovering over one spot for
too long. Here again, can`t rule out an inch or two on
grassy/elevated surfaces but impacts during the day should be
minimal.

Phase #2.b Intense Lake Effect Sunday Night into Monday...

There may be a brief lull in activity Sun evening but things change
quickly overnight. A piece of the Arctic upper low will come
crashing down the lake Sun night. Inversion heights disappear with
incredibly steep lapse rates all the way to the tropopause producing
lake-induced CAPE values potentially over 1000 J/kg by early Mon
morning. Surface temps also crash into the low 20s which will
severely limit any melting potential. Models hinting at a "type-6"
event (dominant band with a mesolow on the end) with mesolow
potentially arriving 06-12Z Mon morning. There is still some
uncertainty in both if a mesolow develops and where it, or the
dominant band, actually set up but current best guess is over
LaPorte or Porter County. Given the incredible thermodynamics, Lake
Superior connection, and synoptic support any mesolow or dominant
band will be capable of producing snowfall rates of up to 3"/hour
with thundersnow quite possible. There is still some uncertainty
where exactly the band sets up and how long it stays in one area
(models show some variation to the flow through Monday), but snow
will be measured in feet, not inches, for any location that sees
this dominant band visit for more than a few hours. Have a
conservative 6-12" for La Porte County right now but that could
certainly go higher. Winds will also be a concern with this event.
Sustained winds around 10 mph with gusts of around 20 mph may cause
some blowing and drifting in areas that see a lot of snow.

A watch seems like a slam dunk at this point but where and when are
difficult questions. Some hi-res models indicate very little break
between the marginal LES Sunday and more intense band Sun night.
Other models show a sizable break. Given the timerange and
uncertainty, opted for a 21Z start time as that is when melting
concerns subside and any precip will likely be snow (possibly
starting to stick to the roads). However, it is possible for it to
be dry in the 21-06Z period in which case the start time could be
moved back. The Monday commutes are by far the more concerning.
Predicting the inland extent is also difficult, especially in light
of a possible mesolow. Negative theta-e lapse rates extend pretty
far inland, especially during the day Monday, which could allow lake
effect band to move far inland. Expansion into a tier of counties
both south and east may be necessary but confidence is not high
enough for a watch in those counties yet. Likewise, it remains
possible the dominant band sets up just to our west Mon morning.
Flow eventually backs NW later Mon but it would also disrupt the
band and significantly lower snowfall rates as it swings through our
counties. Putting it all together, felt confident enough in a watch
for La Porte and surrounding counties but it is just a watch and
further changes in timing and coverage are certainly possible as we
narrow down the forecast.

LES should wind down by Mon night as flow continues to back
westerly, inversion heights crash, and dry air take an increasing
toll. LES ends everywhere by Tue AM but a warm front brings more
light precip chances later Tue. A brief mix is possible at the onset
but this will likely be primarily rain. The corresponding cold front
then swings through on Wed with some minor lake effect precip
possible in our north again. Quiet wx finally returns Thu-Fri.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 614 AM EST Sat Nov 8 2025

Weak convergent boundary with minor CAA supporting some stratus
and light rain around KSBN. This stratus will spread SE through
the morning but ceilings should also climb slightly with
daytime heating...becoming VFR by midday. Attention then turns
to next trough and surface low swinging through the area
tonight. Widespread rain is expected to start the night with a
changeover to snow from north to south during the overnight.
There is still some uncertainty in the exact changeover times
but regardless, IFR conditions are likely.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Winter Storm Watch from Sunday afternoon through Monday
     evening for INZ012-014-103-104-203-204.
OH...None.
MI...Winter Storm Watch from Sunday afternoon through Monday
     evening for MIZ177-277.
MARINE...Gale Watch from Sunday morning through Monday morning for
     LMZ043-046.

&&

$$

DISCUSSION...AGD
AVIATION...AGD