523
FXUS63 KIND 131721
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1221 PM EST Sat Dec 13 2025

.KEY MESSAGES...

- Winter Storm Warning for the I-74 Corridor.
- Winter Weather Advisory most other areas Saturday into Saturday
evening.
- Cold Weather Advisory all areas Sunday morning.
- Accumulating snowfall will occur midday Saturday into Saturday
evening. Three to 5 inch accumulations will be common, with higher
amounts possible.
- Arctic outbreak late Saturday to Monday morning. Low temperatures
  below zero...dangerous sub-zero wind chills down to -20F.
- Moderation through mid-week to above normal temperatures...rain
  chances Wednesday night-Thursday

&&

.FORECAST UPDATE...
Issued at 941 AM EST Sat Dec 13 2025

The forecast remains mostly on track with only a few minor
adjustments made to POPs and temperatures. Latest KIND radar imagery
and surface observations depict light snow is ongoing across the
western half of central Indiana and as far east as the Indianapolis
metro. Snowfall rates are light at this time due to weak overall
forcing. However, stronger frontogenetical forcing currently over IL
will overspread the area later this morning and into the afternoon.
Look for snowfall rates to quickly pick up once the stronger forcing
moves in. Expect road conditions to deteriorate quickly once these
higher rates begin as well.

It appears ongoing light snow is mostly located near the I-70
corridor and south. Locations further north still have dewpoint
depressions around 10F. Evaporative cooling should quickly saturate
this pocket of drier air in the next hour or so with snow beginning
near Lafayette by late morning and rapidly spreading eastward
towards midday.

&&

.SHORT TERM (Today and tonight)...
Issued at 346 AM EST Sat Dec 13 2025

Surface analysis early this morning shows deep and cold low pressure
over northern Ontario. This was resulting in cyclonic flow across
the Great Lakes and Indiana. A strong area of high pressure was
found stretching from southern Central Canada sagging down across
the plains to the middle Mississippi Valley. A weak surface ridge
extended east from the high across KY. Aloft, strong and fast flow
was in place, stretching from the Pacific northwest across the
Rockies to KY and TN. A deep upper low was found over Ontario. An
upper level short wave was found over the northern plains within the
flow aloft, moving quickly southeast. This feature was producing
some snow over MT and SD. This will be our main weather feature for
today.

Today...

***Impactful snow through the day across most of Central Indiana***

***WINTER STORM WARNING for the I-74 corridor***

***WINTER WEATHER ADVISORY REMAINS IN EFFECT for much of the rest
 of CENTRAL INDIANA***

Models suggest the quick moving short wave over the northern plains
will quickly push to Indiana and the Ohio Valley today, providing
strong forcing upon arrival. Strong jet dynamics aloft will also be
a key player today. Forcing should start arriving by mid day and
persist through the afternoon before tapering off this evening.
Forecast soundings show the arrival of a deeply saturated column
this afternoon, persisting for 4-6 hours. During this time the
dendritic growth zone of -10 to -20 remains fully saturated,
favorable for snow. Mid levels in the models do a good job showing
the arrival of the anticipated moisture just before 18Z and its
departure just after 00Z. HRRR also suggests a swath of snow moving
across Central Indiana from 16Z through 02Z. Thus many signals are
present for this clipper snow event and confidence remains high.
Highest snow totals should be along an I-74 corridor, impacting
Lafayette, Crawfordsville. Indianapolis, Shelbyville, Rushville and
New Castle. Overall amounts should range from 3 to 5 inches across
the forecast area, but locally higher amounts, perhaps around 6
inches will be possible in the corridor listed above. Colder
temperatures and the favorable DGZ, should lead to higher snow
ratios. Thus have decided to issue WSW for that area.

The lighter snow and gusty winds around 15 mph may result in some
blowing and drifting snow today and tonight, particularly on N-S
roads in rural areas. Cold air advection will be ongoing today as
the arctic air begins to arrive in the area. THis will result in
falling temperatures through the day and high temperatures reached
early in the day. This will result in wind chills in the single
digits.

Tonight...

As the upper wave quickly departs this evening, best moisture and
forcing will exit by 03Z. Pops may still be needed for a short
window of 00Z-02Z, but the majority of the night will be dry and
very cold as the arctic air mass associated with the advancing high
pressure system arrives in Indiana. By 12Z Sunday, 850mb temps are
suggested to reach around -18C. With new snow fall and clearing
skies through the overnight period, temperatures will fall to the
low single digits at most locations with values below zero at many
spots. Ongoing cold weather advisory for this period will be on the
mark.

&&

.LONG TERM (Sunday through Friday)...
Issued at 346 AM EST Sat Dec 13 2025

Sunday through Monday...

An awaited transition to dry conditions will occur as the page turns
into the long term, but at the expense of a potent early-season
arctic outbreak...that will bring sub-zero mornings and dangerous
wind chills Sunday into Monday morning.  Amplified 1044 mb surface
ridge crossing much of central North America, will be centered over
the Middle Missouri River Valley early Sunday...shifting to the
central Appalachians by the early Monday timeframe.  Solid pressure
gradient will continue 10-15 mph northwest winds gusting to 20 mph
or so...with flow waning through late day and early evening hours as
the center of the ridge nudges into the CWA from SW to NE.  Winds to
become light Sunday night as the arctic dome slides over the region,
before stronger, now south-southwesterly, breezes resume going into
Monday morning.

Temperatures will likely start in the negative single digits early
Sunday under partly to mostly clear skies and amid the fresh, fluffy
snowpack.  Readings to struggle to climb during the day Sunday with
single digits the rule most of the day...and likely even colder
marks Sunday night per the light winds and moderate snow depth
easily allowing radiative cooling processes.  Isolated negative 10
or lower lows Sunday night are certainly possible over central/
northern counties.  Moderate confidence in Monday`s maximums
reaching the 20s for most locations with the arctic high departing
fast enough to bring substantial warm advection.

Wind chills will most likely be worst early Sunday given the
lingering winds, with widespread negative 10 to negative 20 minimum
values.  Current Cold Weather Advisory in effect until 100 PM Sunday
may potentially be extended or even upgraded to an Extreme Cold
Warning...especially if the short term snowfall overperforms.
Subzero wind chill values much of the day Sunday should actually
improve into Sunday evening with the diminishing winds.  Wind chills
to fall yet again with increasing, warm-advective, return
flow...which should unfortunately begin pre-dawn Monday...allowing
negative 10 to negative 20 wind chills for consecutive nights.  Wind
chills to improve to 10 to 20 degrees by late Monday from noticeably
higher temperatures.

Tuesday through Friday...

Moderate southerly breezes, courtesy of much-weaker surface high
pressure lingering over the southeastern US...will maintain steady
moderation through the mid-week. Afternoon highs climbing from the
30s Tuesday, to 40s Wednesday...will continue to moderate to around
50F for Thursday, with perhaps robust southerly gusts overcoming any
cooling effects of scattered/numerous rain showers around the
Wednesday Night-Thursday timeframe ahead of the next potent system`s
cold front.  Overall zonal upper level pattern into the late week
should prevent another arctic invasion, despite strong storm system
crossing Ontario.  Seasonably cool conditions expected as the long
term period ends.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 1221 PM EST Sat Dec 13 2025

Impacts:

- Widespread snow with IFR and occasional LIFR visibilities diminish
  after 13/2300Z
- A return to VFR after 14/0500Z

Discussion:

Bands of moderate to heavy snow with IFR and occasional LIFR
visibilities from 1/4 to 1/2 mile will continue to affect the area
through 23Z, before a quick diminishing trend to MVFR and then VFR
visibilities from west to east between 23-02Z. The only terminal
that may not see a prolonged period of LIFR through 00Z will be KBMG
since they will remain on the southern fringes of the strongest
forcing aloft. Winds will remain 8-12 kts from the NW through the
period as arctic high pressure builds down into the MS valley.

As drier air works its way into central Indiana, expect MVFR
ceilings to give way to VFR conditions after 05Z.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until midnight EST tonight for INZ021-
031-041-042-060>063-070>072.

Cold Weather Advisory from midnight tonight to 1 PM EST Sunday
for INZ021-028>031-035>049-051>057-060>065-067>072.

Winter Storm Warning until midnight EST tonight for INZ028>030-
035>040-043>049-051>057-064-065.

&&

$$

UPDATE...Melo
SHORT TERM...Puma
LONG TERM...AGM
AVIATION...Crosbie