793
FXUS63 KIND 110750
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
250 AM EST Thu Dec 11 2025

.KEY MESSAGES...

- Accumulating snow likely Thursday night into Friday morning with a
  narrow swath of 3-5 inches of snow

- Second round of accumulating light-moderate snowfall Saturday
  midday to evening

- Arctic outbreak late Saturday to Monday AM...low temperatures near
  or below zero...dangerous sub-zero wind chills down to -20F.

&&

.SHORT TERM (Today and tonight)...
Issued at 250 AM EST Thu Dec 11 2025

Central Indiana will now face a succession of Alberta Clipper lows
Central Indiana will remain in the path of strong upper level NW
flow, and an efficient set up for quickly developing lows out of the
Canadian Rockies. The second of these systems is expected to pass
through late Thursday through Friday morning. Prior to its arrival,
weak low level vort maxes interacting with lingering stratus in the
broader cyclonic flow will likely lead to scattered flurries this
morning and into the afternoon. These should not accumulate to
anything, but provide periodic snowflakes across the region.

The previous system brought through strong CAA, of which sank the
baroclinic zone southward placing central Indiana in an ideal zone
for both cyclogenesis and temperatures cold enough for snowfall.
This second low will be weaker than Wednesday`s system, but will
likely still have just as much forcing as it pushes across the strong
baroclinic zone.

These clipper systems along strong temperature gradients typically
produce narrow corridors of moderate QPF, and this one is expected
to be no different with a general 50-75mile wide corridor of highest
QPF. Members of the HREF are still unaligned on expected placement
of this corridor leading to some uncertainty with only 15 to 18
hours until precipitation onset. The current range of potential
outcomes includes as far north as a Crawfordsville to Newcastle
line, to as far south as Vincennes to French Lick. That said, the
greatest likelihood for this corridor is still along or just south
of the I-74 corridor including cities like Greencastle, Bloomington,
Columbus, and Seymour.

When looking at snow totals, there are multiple things to keep in
mind but the main two are overall QPF and SLRs. Model soundings
showcase a deep isothermal layer as the low arrives between -6C and -
10C. This isn`t the most ideal temperature for efficient dendrite
growth, but deep saturation above 6km and surface temperatures
remaining 5-6 degrees below freezing should lead to SLRs between 12-
14:1 across most of central Indiana. Clipper system tend to be on
the lower end for QPF due to weak moisture return but given a
prolonged 9 to 12 hour stretch of snowfall, total QPF amounts of
0.25-0.35 looks to be the likely peak for the greatest corridor.
This should lead to a swath of snowfall between 3 and 5 inches.
Slightly higher amounts are possible where the strongest
frontogenetical forcing occurs as this forcing will likely be
slightly further aloft and within more ideal DGZ temperatures.

Forecast timing has a bit more confidence, as the margin of error is
larger and ensembles have a tighter spread. Currently, snow is
expected to reach the Indiana border between 4PM and 7PM on Thursday
and exit Friday morning between 5AM and 8AM.

&&

.LONG TERM (Friday through Wednesday)...
Issued at 250 AM EST Thu Dec 11 2025

Coldest portions of a very large and anomalously cold arctic surface
ridge that will prevail over Indiana late Saturday to Monday
morning...will be bookended by more reasonable early-weekend cold
with another light to moderate snowfall event through PM hours
Saturday...and steady moderation through the early workweek to
seasonable readings by the end of the period.

Lingering snow showers from the short term`s boisterous clipper
system should last into Friday morning across most of the region,
especially eastern zones that could see an additional very thin
coating after daybreak.  Central/southern zones to likely creep
above freezing Friday afternoon...which will be the last time until
at least Tuesday.  Only light to moderate wind gusts to end the
workweek behind the departing system...as large upper polar trough
occupying much of North America...adjusts around a broad embedded
short wave crossing the northern Great Lakes, bringing brief zonal
flow over the Midwest.  Nevertheless, Friday night will be
noticeably colder than the short term, with lows in the teens to
around 20F for most spots, and some stronger gusts nearing 20 mph
dropping wind chills as low as single digits for much of the CWA.

Biggest precipitation event for the long term will be yet another
clipper-type system within the overall west-northwest flow...
streaming east within the midday to evening hours. Moderate
confidence in widespread 0.10 to 0.20 liquid equivalents...yet less
certainty in location of embedded heavier bands closer to 0.25
inches, although greatest likelihood south of the I-74 corridor.
While this episode should once again feature a thermal profile below
H600 generally around negative 10 degrees Celsius...guidance is
showing a growing DGZ presence through the latter half of the
episode for the I-74 corridor and north.  Resultant increase in SLR/
fluffier snow for late day/evening hours would help boost total
snowfall for these areas north of the main swath, bringing the
potential for 2-4 inches of new snowfall over most of the region.

Cold conditions including dangerously low wind chills will be the
long term`s greatest hazard.  This will starting Saturday for at
least northwest counties, where the earlier onset of snow will hold
readings in the teens.  West-northwest to northwest cold advective
breezes gusting to 15-20 mph will be the rule late Saturday through
Sunday afternoon as the arctic surface high`s center tracks from the
Canadian border to Illinois.  The departing clipper will allow skies
to clear late Saturday night, with the fresh addition to the snow
pack contributing to overnight lows in the negative single digits,
and therefore dangerous wind chills falling from around 5 above to
perhaps negative 15 to negative 25 degrees.

Sunday should be the only bitterly cold daytime when most locales
may fail to climb above the single digits, with wind chill values
possibly held below zero throughout the breezy day.  Higher
confidence in another dangerously cold night to end the weekend with
lows again likely dropping into the negative single digits...
although lighter winds should partially mitigate wind chills with WC
values potentially falling to Advisory criteria for a second night.
Welcomed moderation progged for the early to mid-workweek...with
solid resurrection of readings around the Monday timeframe hopefully
thwarting any further negative wind chills.

Lower confidence in timing/amounts of any weakly-forced
precipitation into the mid-week...when transition to more zonal
upper pattern allows slow increase of broad Gulf moisture to overrun
the Ohio Valley and possibly the Midwest...with perhaps a few rain
showers that could have an icy onset if only from very cold ground
tempertures.   The current forecast maximum temperatures across the
region Wednesday are 39-46F.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 1209 AM EST Thu Dec 11 2025

Impacts:

- MVFR ceilings with flurries/light snow showers tonight
- MVFR conditions continue through midday Thursday
- Snow arrives with rapidly deteriorating conditions early Thursday
evening

Discussion:

Scattered light snow showers and flurries continue this evening
under a predominantly MVFR ceiling. Scattered light snow showers
and flurries will linger for much of the night then diminish
Thursday morning as weak surface ridging builds in. Northwest
winds continue to gust near 25kts currently but should drop off by
late evening as the pressure gradient relaxes.

MVFR stratus will hold Thursday morning but should see ceilings rise
up to low VFR levels for most of the afternoon as the surface ridge
axis passes through the Ohio Valley. Westerly winds will back to
southwest by late day at less than 10kts.

Widespread snow will expand into central Indiana from the northwest
by early Thursday evening with conditions rapidly deteriorating
through the evening as snow rates increase.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 5 PM this afternoon to 10 AM EST
Friday for INZ028>030-035>037-039-043>048-051>057-060>065-
070>072.

&&

$$

SHORT TERM...Updike
LONG TERM...AGM
AVIATION...Updike