488
FXUS63 KIND 112256
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
556 PM EST Thu Dec 11 2025

.KEY MESSAGES...

- Accumulating snow tonight into tomorrow morning with a narrow
  swath of 2-5 inches over the southwest half of central Indiana

- Second round of accumulating snowfall Saturday midday to evening

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

&&

.MESOSCALE UPDATE...
Issued at 556 PM EST Thu Dec 11 2025

Snow has arrived with the approaching clipper across the lower
Wabash Valley as of 2230Z with confirmation from multiple sources in
Knox and Daviess Counties. To this point...this is where the snow is
confined other than the flurries that have been ongoing in the Indy
metro all afternoon.

Radar trends continue to support the focus for greatest impacts and
heaviest snowfall across the southwest portion of the forecast with
growing confidence in lower snowfall for the northeast half of
central Indiana. Besides the orientation of the clipper at this
point...the presence of lingering dry air in the 850-700mb layer is
going to be problematic with snow onset and intensity essentially
northeast of the I-74 corridor. Still anticipate a few hours with
moderate snowfall in this corridor from late evening into the
overnight as the clipper pivots but remain a bit concerned that
forecasted snowfall amounts remain a touch high on the northern
flank. This will likely impact Lafayette and the Indy metro...with
the possibility for a wide variance in amounts across the metro from
northeast to southwest. Quite conceivable that locations like
Fishers and Noblesville only see an inch or so while Mooresville and
Plainfield see 2-3 inches. Not planning any changes to the forecast
amounts at this point but will monitor trends over the next few
hours.

Expect a gradual expansion to the snow through the evening but have
slowed arrival times down by 1 to 3 hours based on thoughts above...
especially across the northeast half of the forecast area.

&&

.SHORT TERM (This evening through Friday)...
Issued at 308 PM EST Thu Dec 11 2025

A round of accumulating snow is in the forecast tonight through
tomorrow morning for portions of Central and South Central Indiana.

A clipper system developing on the lee side of the Rockies
traverses eastward across the Plains tonight then just south of the
state by the morning hours. Aloft, a 140 kt jet streak from British
Columbia to Indiana has induced surface cyclogenesis on the lee side
of the Rockies in Wyoming and Colorado. The low is expected to track
along a tight low level thermal gradient separating an incoming
arctic airmass to the north and a very warm airmass over the Plains.
Today`s guidance has continued the trend of shifting the track of
the low southward about 50 miles, along with the axis of heaviest
precipitation. The forecast has been adjusted to account for the
southward shift.

By tonight, a 140 kt jet streak overhead, places Central and
Southern Indiana within the right entrance region, in an area of
enhanced lift. Latest guidance places the best low to mid level
frontogenetical forcing along and southwest of the I-74 corridor in
the 03z-09z timeframe tonight. Despite a lack of strong moisture
advection ahead of the system and little to no Gulf moisture
interaction, frontogenesis and lift within the exit region of the
jet will work together to squeeze out what moisture is available and
lead to isolated areas of higher snow amounts. Best forcing for
ascent within the dendritic growth zone occur from around 00z-08z,
before mid level dry air work its way in. This is the timeframe
where snow to liquid ratios will be highest (drier snow). After the
2-4am timeframe, the low level thermal profile becomes marginal for
dendritic growth, so expect lower snow to liquid ratios on the back
half of the snow event and as things taper off Friday morning.

With all this said, while it is not a perfect scenario for efficient
snowfall production and higher accumulations, enough parameters are
coming together to support a period of accumulating snow tonight
across portions of Central and South Central Indiana. With the
southward shift in all guidance, the narrow axis of highest snowfall
amounts look to be south of the I-74 corridor with 3-5" possible
from Terre Haute to Bloomington to Seymour.  Isolated 6" amounts are
expected within the axis of higher snowfall, but confidence is not
high enough in widespread 5-6+ inch amounts to warrant upgrading the
advisory. Confidence is increasing in amounts closer to 1-3 inches
for the Indianapolis metro and counties along I-74, with a sharper
cut off as one heads northward. Will need to watch southwestern
Indiana overnight tonight as the low may track overhead and push
enough low level "warm" air in to raise temperatures above freezing
in the vicinity of Knox, Martin, and Daviess counties. If this
happens, a changeover to rain may occur briefly, keeping snow
amounts on the lower end of the forecast ranges. Lowest confidence
areas are on the edges of the snow band, just north of Indianapolis
and on the far southern edge of the system as any wobble in the axis
of heavy snow, even by 25 miles, can mean the difference between one
inch of snow and several.

For timing, isolated snow showers have been ongoing across Indiana
today however steadier can be seen on radar already beginning across
Illinois. By 5 PM, light snow should be beginning along the IL/IN
state line, then advance eastward after sunset. The best dynamics
for heavy snow align from around 8PM to 3AM, then lighter snow
expected through the rest of the morning hours before tapering off
from west to east. No changes made to the Winter Weather Advisory.
Expecting widespread travel impacts for the Friday morning commute,
then improving conditions midday Friday as temperatures rise to or
above freezing in many locations.

&&

.LONG TERM (Friday night through Thursday)...
Issued at 308 PM EST Thu Dec 11 2025

More accumulating snow followed by dangerously cold wind chills can
be expected Saturday into Sunday.

Another round of upper energy along with incoming Arctic air on
Saturday will provide forcing. The area will be in the right rear
quadrant of an upper jet will also add forcing, and there is some
potential for frontogenetical forcing. Moisture will still be
around, and the incoming Arctic air will help squeeze out moisture
as well.

Thus, expect another accumulating snowfall Saturday into Saturday
evening. Current thinking is another 2 to 4 inches for much of the
area. However, guidance is still differing on the location of the
axis of higher totals, with the NAM noticeably north of most other
solutions. Amounts will also be harder to pin down for some areas as
the snow ratio increases with colder air filtering in.

After the forcing ends and snow exits, Arctic high pressure will
increase its influence on the area, bringing drier air and
decreasing clouds. Winds will remain up through Sunday morning, so
radiational cooling won`t be strong. However, the airmass will be
cold enough to bring subzero temperatures to much of the area, with
near zero readings elsewhere. Wind chills will approach -20, so cold
headlines will likely become necessary.

Sunday will be cold and dry as the high moves in. Highs will
generally be in the single digits, and Indy`s record low maximum
temperature of 9 degrees will be in jeopardy. Winds will diminish,
but subzero wind chills will continue.

Sunday night looks to be the coldest night with mostly clear skies,
light winds, and the fresh snow cover from Saturday. Lows will
likely be below zero most areas, with the potential for near -10
readings at a few locations. Minimums may occur early in the
overnight as winds do increase a bit later in the night. With
lighter winds, wind chills won`t be quite as cold as the previous
night, but still bitterly cold.

The high pressure will move off to the southeast for early next
week, allowing warmer air to return. Mid-week upper flow will be
near zonal. This will result in highs returning to the 30s Tuesday
and to the 40s for Wednesday and Thursday.

A system could bring some rain later Wednesday into Thursday, but
details on timing and strength still need to be determined.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 541 PM EST Thu Dec 11 2025

Impacts:

- Snow arrives with rapidly deteriorating conditions early this
evening, especially at KBMG and KHUF
- Sub-IFR conditions expected from late evening through early Friday
- Snow ending early Friday morning
- MVFR ceilings linger all day Friday

Discussion:

Widespread snow will expand into the region from the west this
evening with conditions rapidly deteriorating as the evening
progresses...especially at KBMG and KHUF. Greatest impacts are
expected are expected at those two terminals with brief periods of
heavy snow and 1/4SM visibilities in the 03-08Z timeframe. KIND and
KLAF will likely experience a 2-4 hour period of moderate snow
overnight as well. Conditions improve slowly in the predawn hours
and through daybreak from northwest to southeast as snowfall becomes
light and ends. Ceilings will slowly improve back to 1500-2000ft by
the afternoon but hold firm through the end of the forecast period.

Light E/SE winds are expected into Friday morning...then shifting to
northwest at less than 10kts in the afternoon.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 10 AM EST Friday for INZ028>030-
035>037-039-043>048-051>057-060>065-067>072.

&&

$$

MESOSCALE...Ryan
SHORT TERM...CM
LONG TERM...50
AVIATION...Ryan