926
FXUS63 KIWX 300430
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1130 PM EST Sat Nov 29 2025

.KEY MESSAGES...

- Widespread snow will persist through Sunday morning w/
  significant accumulations expected.

- Snow will begin diminishing in coverage and intensity
  overnight, but lake effect snow showers are expected to
  develop again on Sunday with some additional travel impacts
  expected.

- Another round of light snow is possible Monday night into early
  Tuesday followed by a stronger intrusion of cold air later in
  the week.

&&

.UPDATE...
Issued at 707 PM EST Sat Nov 29 2025

Snow amounts so far have been right around what was expected.
Area of better instability aloft is moving into the region so
precip is transitioning to more banded/cellular and that will
continue through 06Z. Convection well to our south is
interrupting northward moisture transport a bit but there are
still pockets of heavy snow moving into our area through 06Z.
After 06Z, midlevel moisture will be lost and surface temps will
climb just above freezing in our SE half. Thus, precip will
transition to drizzle before ending from west to east in the
06-12Z window. Overall forecast remains on track and only minor
updates to slightly lower overnight total snow amounts. Still
expecting a brief window of favorable lake effect parameters
roughly 15Z-00Z Sunday which could easily drop another 2-5" in
our NW zones yielding storm total amounts over a foot. Also
added a blowing snow mention. Already getting reports of
blowing/drifting snow and wind speeds will only increase through
Sunday. No changes to headlines at this point.

&&

.DISCUSSION...
Issued at 126 PM EST Sat Nov 29 2025

The inherited forecast remains very much on track w/ minimal changes
necessary to ongoing messaging. Snow has already overspread much of
the area this afternoon and will likely continue to increase in
intensity over the next several hours. Heaviest snowfall still seems
likely to occur in the 21z to 06z time frame as a strong vort energy
and mid-level speed max interact with broad, intense isentropic lift
across a large portion of the CWA. Greatest accumulations should be
found north of US-24 with a rather sharp gradient expected to the
south courtesy of the impressive low-level warm air advection regime
potentially allowing rain to mix in with the snow for a time, which
would significantly impact total accumulations. Naturally, this will
also influence the character of the snow which is expected to be
very heavy and wet, especially later in the event with the main WAA
push. SLRS will transition from near 12:1 early to around 8:1 late
this evening. A short burst of convectively enhanced heavy
snowfall rates (thundersnow cannot be entirely ruled out) may
occur during the mid/late evening hours w/ the main push of warm
advection aloft. Overall, still looking at decent probabilities
of 6-10 inches of total (system) snowfall accumulation mainly
focused along/north of US-24. Localized lake effect bands on
Sunday may push total accumulations into the 12-14 inch range
closer to Lake Michigan.

Please refer to the previous forecast discussion for a more detailed
meteorological overview. /Hammer

Previous Discussion (Issued 414 AM EST Sat Nov 29 2025):

Just some minor forecast changes made this morning, but overall
messaging remains intact with period of heaviest snowfall and
greatest impacts late this afternoon into this evening. The Winter
Storm Warning and Winter Weather Advisories areas remain intact with
some minor adjustments to ending times of the headlines on Sunday.
Winter Storm Warning headlines continue into Sunday afternoon mainly
for lake effect snow favored areas in phase 2 of this system.

A quick ramp-up of isentropic ascent is expected through the
remainder of the morning hours. An expansive precip shield has
already developed across the Lower/Mid MS River Valley this morning.
Near term progs of 290K surface depict strongest isentropic lift
across northern Missouri/west central Illinois as of 08Z. Short term
progs take zone of strongest ascent on this surface into northwest
Indiana/southwest Lower Michigan by 18Z. Track of this
advective/isentropic forcing may be a little more muted across far
southeast portions of the forecast area this afternoon. Initial low
level thermal/moisture profiles and 285K condensation pressure
deficit analysis suggests that this saturation process could take a
bit longer than previously expected, particularly across eastern
half/southeast portions of the forecast area where isentropic
forcing is slightly weaker. Have made some minor adjustments to
start time of headlines (pushed back 3 hours across the east),
although snow accumulations across northwest Ohio may not occur
until the mid afternoon hours today. Some localized low level fgen
at nose of stronger low level flow could enhance late morning
through mid afternoon snow accumulations for some areas west of I-69.

Guidance has been fairly consistent with handling of this system
although some slight dprog/Dt trends could have an impact. Some
guidance appears a bit more disjointed in handling of mid/upper
level system, with a likely diabatically generated mid level PV
anomaly pushing through this afternoon deriving from ongoing MO/IL
precip. A tendency to perhaps slightly less phasing of primary
synoptic trough and this diabatically generated interior anomaly
appears to be trending solution to slightly weaker (albeit still
quite strong) kinematic fields and consequently just slightly weaker
northward moisture transport. Latest suite of guidance also may not
be quite as supportive for CSI type banding given some weaker
unidirectional mid level wind shear resulting from the above
guidance trends. Nonetheless, very strong advective fields and
increasing synoptic scale support via primary upper trough and left
exit region of central CONUS upper jet streak should support
greatest snowfall rates in the 21z-02Z time period this evening. 00Z
HREF suite also points to this time period as greatest probs of
experiencing 1-2 inch/hour snowfall rates for a time. The strong
warm/moist advection will result in a highly elevated DGZ, although
with some respectable depth of 3-5K feet in the mid levels across
far NW IN/SW Lower Michigan. However, overall snow efficiency still
appears to be limited with this system across most of the area given
strongest lift in lower reaches of DGZ and more limited time window
of better DGZ moisture quality. Event average 9-12 snow to liquid
ratio was maintained in this forecast with warning level snow
amounts dependent on the high QPF nature of this system. Some
concern that relatively narrow window of strongest forcing
mechanisms late afternoon/evening and inefficient snow production
could lead to lower than forecasted snow amounts, particularly east
of I-69. At this time have made only minor adjustments to forecasted
snow amounts through tonight, with just a slightly lower trend in
most places. Highest accumulations of 6 to 10 inches through 12Z
Sunday are still forecasted for northwest third of the area where
some cross-hair signature of mid level lift/DGZ is noted in forecast
time/height sections. Some consideration given to transitioning the
warning to an advisory south of US Route 24 across far northeast
Indiana/northwest Ohio but will allow dayshift to assess trends this
morning.

A mid level dry slot still looks to overspread the area overnight
into early Sunday morning, with a quick tapering of snow across most
of the area and a likely transition to light snow/areas of drizzle
with drying DGZ and near sfc wet bulbs warming to near freezing
across south/southeast areas. A quick transition to stronger low
level CAA ensues for Sunday morning and afternoon as stronger upper
vort lobe drops across the southern Great Lakes. This should allow
for at least a 6 to 9 hour period of favorable lake effect snow
showers for additional accumulations/impacts with gusty CAA-induced
winds also expected. Some higher res guidance also suggests
potential of mesovort-type feature to accompany a sharper low level
trough passage across southern Lake Michigan Sunday morning/midday.
Have maintained the Winter Storm Warning headline into Sunday
afternoon for areas possibly impacted by lake effect snow, and have
expired the warning by 15Z Sunday for remainder of the area. This
timing may need to be moved up further as most of the synoptic
accumulating snow could depart after 09Z Sunday morning. Lake effect
snow showers should wane Sunday evening.

Monday will feature quiet conditions as a progressive low level
anticyclone sweeps across the area, but attention quickly turns to a
lower amplitude fast moving system for Monday night/early Tuesday.
Primary low level baroclinic zone and better moisture will be
initially suppressed well south, but a period of northward moisture
transport is expected across the Ohio Valley ahead of this system.
Guidance differs with details in the amplitude of this wave and
northward extent of sfc reflection/moisture return. Even if a more
suppressed sfc reflection verifies, would expect a strong mid level
baroclinic zone to be in place locally, with fgen band likely to
affect area with some additional snow accumulations Monday
night/early Tuesday that could bring an additional 1-3" of snow
across the area. Thus, have accepted the sharp ramp-up in PoPs for
this period suggested by the model blended guidance.

No major changes to the extended forecast at this time with fuller
latitude longwave trough bringing stronger cold frontal push for the
Wed-Thu timeframe. Some single digit lows are possible Thursday
night under the influence of sfc high pressure, also aided by
potential of some light additional fresh snowcover with the frontal
forcing. Some moderation in temperatures is possible by next
weekend, but still below normal for early December. /Marsili

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1130 PM EST Sat Nov 29 2025

System snow associated with strong isentropic ascent in the warm
sector of passing low is now exiting and weakening. Midlevel dry
slot will move over the area in the 06-09Z window and bring an
end to moderate/heavy snow with slowly improving visibilities.
(Some IFR stratus will still be possible through the early
morning, though.) Lake effect snow showers are then expected at
KSBN for much of the day, though there will be break at times
with some uncertainty on exact timing and strength of lake
effect snow. Lake effect snow showers may impact KFWA during the
afternoon as well but confidence is much lower there. Both sites
will trend toward VFR by Sunday evening as dry air finally
advects back into the area.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Winter Storm Warning until 7 PM EST /6 PM CST/ Sunday for
     INZ005>008-012-014-103-104-116-203-204.
     Winter Storm Warning until 10 AM EST Sunday for INZ009-013-015-
     017-018-020-022>027-032>034-216.
OH...Winter Storm Warning until 10 AM EST Sunday for OHZ001-002-004-
     005-015-016-024.
     Winter Weather Advisory until 10 AM EST Sunday for OHZ025.
MI...Winter Storm Warning until 7 PM EST Sunday for MIZ078>080-177-
     277.
     Winter Storm Warning until 10 AM EST Sunday for MIZ081.
MARINE...Small Craft Advisory until 8 AM EST Monday for LMZ043-046.

&&

$$

UPDATE...AGD
DISCUSSION...Hammer
AVIATION...AGD