517
FXUS63 KIND 120829
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
329 AM EST Fri Dec 12 2025

.KEY MESSAGES...

- Snow ending this morning with total accumulations of 2-5 inches
  along a Terre Haute-Martinsville-Columbus line. Lesser final
  totals north.

- Second round of accumulating snowfall Saturday midday to early
  evening...with blowing and drifting of snow possible

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

&&

.SHORT TERM (Today and tonight)...
Issued at 323 AM EST Fri Dec 12 2025

Surface analysis early this morning shows a broad area of weak high
pressure stretching from WI...across MI to OH and WVA. Low pressure
was found over OK, with a warm frontal boundary stretching east
across MO, southern Illinois to Southern Indiana. Aloft, water vapor
showed a quick northwest flow was in place, streaming across Indiana
from the Pacific northwest and western Canada. Radar trends show
areas of snow, mainly across the southwestern two-thrids of Central
Indiana pushing southeast. This was associated with quick moving
upper level forcing dynamics within the flow aloft. Back edge of the
snow was found over Central Illinois and some echos have shown a
diminishing trend.

Today...

Ongoing snow will be rapidly moving to the SE early this morning.
HRRR suggests the progression should result in an end to snow by 10Z-
12Z across the forecast area as the upper forcing quickly departs.
Over the later part of the night, the most impacted area will remain
to be along and southwest of a Terre Haute to Martinsville to
Columbus line, including Bloomington. Given observational trends, a
few additional inches will be possible through 12Z, and some totals
could reach 5-6 inches.

Lesser amounts will be found north at Indianapolis and Lafayette,
with 1-2 inch amounts. These snows will continue to be enough to
cover roads and cause slippery conditions during the morning rush
hours. Ongoing Advisory will remain in place and a difficult commute
could be in store this morning.

As the day progresses...the surface low pressure system will
progress eastward into the Tennessee valley and this will become
less impactful for Indiana as strong and cold high pressure over the
northern plains begins to spill southeast toward Indiana. Forecast
soundings start the day saturated as the short wave departs, but
trend toward a dry column later in the day as the cold high pressure
arrives and top down subsidence is prevalent. Time heights and
forecast soundings show trapped lower level moisture which will lead
to cloudy skies through the day. Little overall change in the
airmass is expected, and this will lead to highs mainly in the lower
30s.

Tonight...

Quiet weather is expected tonight as another quick moving cold front
pushes toward Indiana, arriving near 12Z. Through the evening and
much of the overnight hours, forecast soundings remain dry as lower
level ridging remains in place ahead of the advancing area of high
pressure. Overnight, the northwest flow remains in place aloft, but
forcing and a subtle short wave appears on our doorstep aloft for
Saturday. Forecast soundings show trapped lower level moisture
through the night tonight. However as the night progresses, dry air
aloft begins to trend toward a top down saturation as the night
progresses. Thus a cloudy and cold night will be expected with lows
around 20.

&&

.LONG TERM (Saturday through Thursday)...
Issued at 323 AM EST Fri Dec 12 2025

Saturday through Monday...

A mainly moderate snowfall focused over afternoon to early evening
hours Saturday will be followed by a bitterly cold arctic outbreak
that will bring dangerously low wind chills through Monday morning.
Continued unseasonably cold pattern of west-northwest flow amid
lowered heights...will see an embedded short wave plunging from the
Canadian Plains into the Midwest, while phasing with and around a
cut-off H500 low twisting over Lake Superior...intensifying the next
clipper system as it quickly crosses the Midwest from west to east.

Colder surface temps Saturday falling from the lower 20s to mid-
teens...along with a colder column that will have an increasing
presence within the dendritic growth zone as the phasing trough
quickly plows across the CWA...will promote higher snow to liquid
ratios trending upward around the 15:1 to 20:1 range.  Heavy to
briefly intense snowfall accumulation rates are certainly on the
table for Saturday afternoon, especially for locations along and
north of the axis of max liquid precipitation (aligned near the I-74
corridor to east-central counties) where SLR will start and trend a
bit higher than southern zones.  The last portions of this snow
episode, through early evening Saturday, could have surprisingly
efficient accumulation rates despite intensity tapering down as SLRs
climb above 20:1.  Unlike the snow event ending during the short
term, winds will be a factor on Saturday with northwest gusts up to
15-20 mph for many spots...which will combine with the fluffier snow
to promote some blowing and drifting of snow.  Storm total snowfall
possibly in the 3-5 inch range for many central and northern
counties may warrant another Advisory...although the impressive rate
of upper level evolution may push the system out to the east faster
which could limit higher end accumulations.

Bitter cold and dangerously low wind chills will bet he next hazard,
immediately on the heels of the departing snow system Saturday
night.  Fresh and perhaps rather deep snow pack along with clearing
skies amid arriving 1045 mb arctic surface high pressure...will
effortlessly drop readings to near/below zero Saturday night.
Excepting a fetch of stratocumulus off of Lake Michigan streaming
over far northeast counties Sunday, mainly clear skies will oversee
15-20 mph northwesterly gusts that will hold temperatures in the
single digits most of the day.  Winds will diminish to light and
variable Sunday night as the ridge`s center drifts east over the
region, allowing one more frigid overnight sporting widespread
negative single digits.  Breezy return flow Monday will make an
impressive first step at rebounding readings into the 20s for much
of the region.

Wind chill values to fall into single digits during Saturday`s snow
burst...and then well below zero Saturday night.  A Cold Weather
Advisory is certainly on the table for the CWA, with an Extreme Cold
Warning not out of the question for at least northwest zones.  Wind
chills to slowly rebound Sunday to around zero...with modest winds
most of Sunday night perhaps preventing criteria-level WC values.
Our Monday morning Chinook may return criteria wind chills before
warm advection wins the battle against the lingering cold.

Tuesday through Thursday...

The mid-week will oversee continued moderation, under a broad zonal
pattern across most of the US...led by south-southwesterly breezes
from the familiar gradient formed between broad ridging to our
southeast and surface low pressure centers crossing the north-
central US.  Moderate confidence in the warm advective surface flow
gusting up to 20-25 mph returning moderate deep moisture for early
winter...yet any forcing retracted to the Upper Midwest/Great Lakes
should maintain precipitation-free conditions through at least
Wednesday.

Temperatures should continue to gain about 10 degrees each day, with
perhaps even a greater upward trend in overnight lows.  Expect all
areas to at least reach the freezing mark Tuesday, with widespread
low 50s possible for Thursday...which would be the first time in
over three weeks.  Plain rain showers also possible by the end of
the period when a weak circulation over the southern Plains may
focus some isentropic lift over the Midwest.  The normal max/min at
Indianapolis through the long term is 40/26.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 329 AM EST Fri Dec 12 2025

Impacts:

- Snow ending by 10Z-12Z
- Continued IFR to MVFR conditions through the TAF period

Discussion:

Quick moving wave aloft will push snow across the TAF sites
overnight. HRRR shows snow ending by 10Z-12Z and have trended toward
VCSH and improved visibilities at that time, however cigs will
remain MVFR or worse through the day.

Some drying and subsidence by late afternoon may lead to high MVFR
cigs by late afternoon.

&&

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

&&

$$

SHORT TERM...Puma
LONG TERM...AGM
AVIATION...Puma