954
FXUS63 KIND 130537
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1237 AM EST Sat Dec 13 2025

.KEY MESSAGES...

- Winter Weather Advisory most 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.

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

- Temperatures will warm to above normal by middle of next week,
  with most snow melted by Thursday.

&&

.FORECAST UPDATE...
Issued at 935 PM EST Fri Dec 12 2025

Cloudy skies across central Indiana this evening. 02Z temperatures
were in the upper 20s and lower 30s.

Overall quiet weather will continue for most of the night as the
region remains shrouded in cloud cover. A cold front currently
moving into northern Illinois will reach the northern Wabash Valley
just prior to daybreak before dropping further southeast on
Saturday. This front is the feature that will allow the surge of
bitterly cold air to overspread the area by Saturday night. Not
entirely out of the question that a few flurries may accompany the
front very late tonight into Saturday morning but expect most areas
remain dry. Temperatures will drop into the teens across the
northern Wabash Valley by daybreak with low to mid 20s further south
across the forecast area.

Onset of snow with the approaching clipper will be as early as 15Z
Saturday in the Wabash Valley then quickly encompassing the rest of
the region through early afternoon with moderate to heavy snow to
follow. Additional details to come with the early morning forecast
package overnight.

&&

.SHORT TERM (This evening through Saturday)...
Issued at 305 PM EST Fri Dec 12 2025

Rest of This Afternoon...

Some partial clearing will persist for a while, but do expect the
clouds to continue to gradually fill back in.

Tonight...

Clouds will help keep temperatures from falling too much for the
night. A cold front will enter the northwest forecast area late
tonight, potentially dropping temperatures there into the teens by
around 12Z. Otherwise, lows in the 20s can be expected.

Saturday...

The cold front will continue to sink south through the day,
gradually lowering temperatures overall. This front may have enough
forcing for a few snow showers in the northern forecast area in the
morning. However, the main forcing for this event will arrive
mid to late morning into early afternoon from the west.

Forcing from an upper trough and the right rear quadrant of an upper
jet will interact with the moisture across the area to produce
snow. In addition, there will be some frontogenetical forcing and
negative EPV above this forcing. This will lead to some more intense
bands of snow. Will have to also watch out for larger dendritic
growth zones.

There looks to be a sharp cutoff to the forcing across the far
southwestern forecast area.

Will go high PoPs most areas Saturday, mainly during the afternoon,
except for the far southwest where only chance to likely PoPs will
be needed due to the sharp cutoff.

Specific amounts will be a bit tricky for a few reasons. First is
that the banding will produce higher amounts in narrow bands that
can cause variability across even within a county. Second is the
sharp cutoff to the south. If that shifts, either direction, amounts
could change more there than elsewhere. Finally, temperatures will
be falling through the day, increasing the snow ratio. Colder
temperatures early could lead to higher snow amounts due to higher
ratios.

Given all of the above, feel that 3 to 5 inches is the most likely
range of amounts for the majority of central Indiana. Areas near
Seymour may be more of a 1-3 or 2-4 situation, while the far
southwest will be a gradient of less than 1 to around 2. Went with a
Winter Weather Advisory for all but the far southwest 3 counties
given these amounts. Locally higher amounts around 6 inches are
definitely possible in the banded heavier snowfall.

Winds will be higher than the last system, and the snow will become
less dense, making for the potential for some minor blowing snow.

Saturday night...

Snow will likely be ongoing at the start of the period across the
southeast forecast area, but this will quickly end as forcing exits
and high pressure builds in. Temperatures will fall, reaching below
zero for the northwest half or so of the area with near zero
elsewhere.

Winds will remain up with the surface high to the northwest, so wind
chills will fall to colder than -10 for the vast majority of the
area during the night. These cold wind chills will last into Sunday.
Thus, have also issued a Cold Weather Advisory from midnight Sunday
to 1 PM Sunday for all areas.

&&

.LONG TERM (Saturday night through Friday)...
Issued at 305 PM EST Fri Dec 12 2025

After a cold and mostly clear day Sunday, another night of frigid
temperatures is expected Sunday night as the 1040 mb high moves
across and just east of the forecast area. Although winds will be
much lighter than Saturday night, actual air temperatures are
expected to be solidly in the 0 to -10F range across the area.
Wind chills look to be anywhere from -8 to -15 degrees late
Sunday night into Monday morning. Later forecasts may need the
inclusion of another cold weather advisory for Sunday night/early
Monday if wind chills look to be colder than -15 degrees.

In the wake of this weekend storm system a major upper level
pattern change will occur for the rest of the extended forecast
thanks to increasing waa, zonal flow and a deepening long wave
trough off along the west coast. 850 mb temps rise from -10C on
Sunday to +8C on Tuesday. The complicating factor for how quickly
surface high temperatures warm along will be the potential affects
of the snow melt /moistening and cool remaining near surface
layer/ beneath a warming aloft. As a result, the current forecast
highs for Wednesday- Thursday may be quite over inflated. In
addition, patchy dense fog may become a factor during this period,
especially in the initial strongest waa period. Later forecasts
will hopefully have more sensible data (including snow pack depth)
which will be a contributing factor to the duration of snow melt
and delay of warmer temperatures.

By Thursday there is agreement of an approaching shortwave and
precipitation back in the forecast across central Indiana. However,
the degree of precip amounts is still highly in question as
variability exists in the strength of this system given the spread
of the GEFS/Euro ensemble members. In general near to slightly below
temperatures are expected Friday ahead of an associated cold front.

In the wake of this shortwave the zonal pattern will reestablish
itself with waa across the central and much of the eastern conus
ahead of the longwave trough off the west coast. The result will be
temperatures warming back above normal by next weekend. Just beyond
the extended, there is a signal for increasing longwave troughing
over eastern canada. This pattern favors shallow arctic air masses
may develop south setting the stage for one of more weak freezing
precip events with any shortwave trough energy emerging out of the
west. Stay tuned.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 1237 AM EST Sat Dec 13 2025

Impacts:

- MVFR ceilings conditions overnight and into Saturday morning.
- Widespread snow with deteriorating conditions near midday Saturday.
- Poor flying conditions, IFR, with moderate to occasionally heavy
snow Saturday afternoon.

Discussion:

MVFR Clouds will persist overnight as quick NW flow aloft will
remain in place. Abundant lower level moisture is suggested to
remain present overnight, resulting in continued MVFR cigs.

A quick moving upper level clipper will sweep across the TAF sites
on Saturday afternoon and evening. Time heights and forecast
soundings show deep saturation and moisture through the afternoon
hours as the forcing passes. Snow will be expected, reducing
visibility to IFR conditions or worse through the afternoon,
resulting in poor flying conditions. Winds around 10-15 mph will may
allow for blowing and drifting snow, contributing to reduced
visibilities.

Snow will end by 00Z-02Z and very cold air arrives on NW winds.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 11 AM this morning to midnight EST
tonight for INZ021-028>031-035>049-051>057-060>065-070>072.

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

&&

$$

UPDATE...Ryan
SHORT TERM...50
LONG TERM...Crosbie
AVIATION...Puma