413
FXUS63 KIND 160531
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1231 AM EST Tue Dec 16 2025

.KEY MESSAGES...

- Isolated freezing drizzle possible Tuesday night generally along
  and north of I-70.

- Widespread moderate rain likely Thursday with minor flooding
  possible.

- Strong winds Thursday evening/night with gusts over 35 mph
  possible.

- Flash Freeze threat Thursday night/early Friday as temperatures
  fall 30-40 degrees in 6-8 hrs.

- Above normal temperatures expected next weekend into Christmas
  week.

&&

.FORECAST UPDATE...
Issued at 1000 PM EST Mon Dec 15 2025

Quiet zonal ridge will prevail through the overnight with recent
arctic ridge having slid to the southeastern CONUS, and any gradient
from next northern system holding off until Tuesday.  Temperatures
are holding steadier than originally expected with ample mid/high
cloud providing adequate insulation...so have delayed decrease of
readings over next few hours and made slight upward adjustments to
low temperatures tonight.  Dry column and lack of forcing amid
modest differential NVA to maintain precipitation-free conditions
tonight.

&&

.SHORT TERM (This evening through Tuesday)...
Issued at 316 PM EST Mon Dec 15 2025

Tonight.

High clouds will continue to stream in from the northwest with
coverage gradually decreasing into the evening as the upper level
flow gradually becomes more westerly vs northwesterly. Wind gusts of
20-25 mph will continue through the remainder of the afternoon with
a 40kt LLJ at 3kft. Weak lapse rates up to this level will help to
limit down the frequency of gusts, but do think at least
occasionally we will see those stronger winds.

Dry and quiet weather is expected for the overnight hours. There may
be some low clouds across the far northwestern counties and the far
south towards daybreak, but coverage will be minimal with a fairly
dry near surface airmass.

Tuesday.

Main focus for Tuesday will be tracking the potential for a very
light precipitation event across southern Indiana towards the late
afternoon and evening hours. Higher resolution models have been
picking up on an area of saturation near the surface with weak lift
in the cloud layer, mainly across southern Indiana which may be just
enough to squeeze out some drizzle or light rain towards the evening
hours. Surface temperatures are expected to be in the mid 30s, but
with a frozen ground there could be some minor impacts on untreated
surfaces due to the recent cold. With plenty of sun expected
tomorrow, the impacts may not be more noticeable until the overnight,
but it will be something that needs to be monitored going into the
day Tuesday.

&&

.LONG TERM (Tuesday night through Monday)...
Issued at 316 PM EST Mon Dec 15 2025

Persistent southwesterly flow will advect deeper low level
moisture noted on satellite imagery over the southern plains into
the region. As we go into Tuesday Night a glancing blow of a
shortwave trough moving through the Great Lakes and a weaker
shortwave trough moving across the MS valley, with an attendant
low-mid level deep convergence zone, may be sufficient to generate
light drizzle. Operational 3km NAM continues to show and several
other CAMs are also showing light QPF Tuesday night. Freezing
drizzle will be possible where surface air temperatures are
expected to range from 30-32 in areas generally along and north of
I-70. Thanks to the recent cold spell experimental NWS road temp
forecast indicates road temps are expected to fall below freezing
by 02Z Wednesday (9 pm Tuesday). The potential exists for minor
ice accumulations on any untreated roads into the early morning
hours on Wednesday before the forcing moves east of the forecast
area. At this time, this freezing drizzle potential will be
mentioned in the HWO with no headlines being issued.

With the continued persistent deep southwesterly low level flow the
warmer/moistening airmass moving over a receding/melting snowpack is
a recipe for fog both late Tuesday night/early Wednesday but even
more so going into Wednesday night. Have added patchy locally dense
fog Wednesday night as snowmelt/cold ground temperatures occur
beneath surface dewpoints in the 30-35F range. Drizzle/light rain
will develop late Wednesday night as low level jet/forcing increase.
Forecast soundings show temperatures just barely above freezing (33-
34) in northern forecast area through 06Z before rising between 06-
12Z Thurs. There is a very slight chance of freezing drizzle during
the 00-06Z period, however will leave this potential out of the
grids/forecast for now given the degree of uncertainty.

A much more pronounced/larger shortwave will move out of the Rockies
into the Plains Wednesday and into the Ohio Valley/Great Lakes
region on Thursday. Strong height falls, ample low level moisture
and a strong cold front spell widespread precipitation Thursday
across the area. NBM pops from 90-99 look very reasonable. Questions
remain on the degree of cooling and any anafrontal forcing that
would support a mix of rain/snow before precip ends Thursday night,
although recent model trends are showing a little better chance of
minor snow accumulations (less than 1 inch) between 00-06Z Friday
before precip ends.

The biggest concerns with this system will be hydrologic, strong
winds and transportation impacts. The hydrologic concerns are
focused on the intensity and amounts of rainfall /pwats near the
90th percentile for Mid-December/. Consensus in model guidance
indicates anywhere around 0.50 to 0.75 inch of QPF, with the recent
runs of the GFS showing up to 1.25 inches for portions of the
forecast area. This moderate to heavy rainfall falling in less than
6 hrs with the main frontal passage Thursday afternoon combined with
the cold ground will aid in enhanced runoff into streams and
potential for some ice jams, as most if not all area creeks and
rivers frozen over at this moment. The saving grace for more
widespread flooding is the lower than average river levels thanks to
the long term drought over much of the area as well as the degree of
ice thickness.

Gradient winds are expected to increase Thursday morning ahead of
the cold front, but the strongest winds are expected to occur
Thursday evening in the wake of the front. GFS model soundings show
momentum transfer of. 35-40 kts winds in the boundary layer to the
surface. Have bumped up wind gusts in NBM to account for this
potential, and headlines for a wind advisory look possible. Lastly,
the transportation concerns are focused on the rainfall washing off
salt on area roads, ponding of water and the increasing threat for a
flash freeze potential Thursday night with temperatures quickly
falling into the 15-20 F range by early Friday morning.

After colder and drier conditions return Friday, another warmup
commences going into next weekend with highs expected to approach 5-
10 degrees above normal Saturday. Deterministic models are in good
agreement with another shortwave increasing rain chances across the
region Saturday night into Sunday. However, spread in ensembles has
been increasing, therefore low end pops seem reasonable. The warmer
than normal temperatures will continue going into Christmas week,
with some indications of highs 20 deg above normal right before
Christmas. Thus the chances of a white Christmas for central Indiana
are looking very very low indeed.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 1229 AM EST Tue Dec 16 2025

Impacts:

- MVFR stratus possible from BMG to IND
- Low-level wind shear after 00z

Discussion:

A trough passing over the northern Great Lakes will promote
increasing southwesterly flow through the TAF period. By tonight, a
strong low-level jet is expected which will result in some low-level
wind shear at all terminals. At the surface, SW winds around or a
little above 10kt are expected as well.

Moisture advection northward by the low-level jet is ongoing from
about St Louis southwestward. There are some indications within
guidance that these clouds make it into Indiana later this
morning. Upstream observations show MVFR ceilings in the
2000-2500ft range. Guidance shows similar ceilings across Indiana,
perhaps dropping a bit below 2000ft due to a cooler boundary
layer with northward extent.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...AGM
SHORT TERM...White
LONG TERM...Crosbie
AVIATION...Eckhoff