textproduct: Indianapolis

KEY MESSAGES

- Narrow convective line with the potential for brief wind gusts in excess of 50mph and perhaps a tornado will move across central Indiana early this evening

- Peak wind gusts at 45 to 50mph across the northern half of central Indiana at times tonight and Monday

- Rapidly falling temperatures into the teens and 20s tonight and Monday with wind chill values near zero at times

- Much colder weather through the upcoming week with chances for light snow Wednesday night/New Year's Eve

SHORT TERM (This evening through Monday)

Issued at 1244 PM EST Sun Dec 28 2025

The primary focus for the short term period will be tracking a potent system this evening into tonight which will bring a line of strong to severe storms, strong gradient winds, and a 40+ degree temperature drop over 6 to 9 hours. As of early this afternoon, skies remain mostly cloudy across the state with winds gradually ramping up as the LLJ strengthens. The surface low associated with the system continues to deepen as it moves across northern Illinois with showers and storms were moving across northern Illinois. These are expected to remain northwest of the forecast area through the remainder of the afternoon with the main timeframe for concern from around 5PM to 10PM as the aforementioned line moves in.

Severe Threat.

Dew points across both central Indiana have risen into the low 60s with most areas now seeing temperatures in the low to mid 60s with increasing confidence in a narrow axis of even higher dewpoints just ahead of the front. High resolution models continue to pick up on a narrow axis of higher dewpoints just ahead of the front which will allow for ML CAPE values of 500-800 j/kg across Illinois where convective initiation is expected. Dynamic indices are all favorable for convection with 0-1km shear upwards of 20kts and SRH values upwards of 300/400 m2/s2. The main question will be how far east the better instability stretches with the loss of diurnal heating towards the time the line crosses into western Indiana. The tornado threat will mainly be across the western and northwestern portions of the forecast area before the loss of instability begins to transition the threat to just damaging winds. With the line expected to become organized, the severe threat will persist through all of central Indiana even as instability drops. While the greater threat will be across Illinois, do have concerns in widespread 40-55 mph winds along the line with sporadic 60-65 mph winds and at least a few kinks in the line which could produce tornadoes.

Gradient Wind Threat.

Outside of storms, gradient winds will gust 40-50 mph along and just behind the line of storms with the stronger gusts with occasional gusts of 35-50 mph continuing through the night. Model soundings show that as the CAA strengthens, the boundary layer never fully decouples with mixing up to around 3000ft through the night. The boundary layer winds will be strongest towards daybreak tomorrow which is when the confidence is highest in the higher-end gusts. Winds aloft will gradually weaken through the day as the system exits which will bring an end to the stronger gusts by the evening.

Flash Freeze and Snow Threat.

The other focus for tonight will be the temperature crash in the aftermath of the frontal passage with a drop from the 60s into the 20s in around six hours. This presents a risk for a flash freeze. While strong post-frontal winds will help evaporate some surface moisture, any residual standing water on untreated surfaces, particularly bridges and overpasses, will likely freeze rapidly before it can dry along with areas where water had ponded earlier in the night. The snow threat looks increasingly minimal tonight as there will be little to no forcing by the time the temperatures drop below freezing. Some snow showers will be possible across the northern counties tomorrow along with flurries to the south associated with the backend of the system but any lake effect snow will remain north of the forecast area based on expected wind fields.

LONG TERM (Monday night through Sunday)

Issued at 231 PM EST Sun Dec 28 2025

A large scale closed low over the Great Lakes to James Bay will dominate the area for most if not all of the long term period, producing dramatically cooler conditions and a couple of opportunities for precipitation amidst a mostly dry stretch for the week.

The coolest temperatures will be early in the period in the wake of the sharp cold front expected this evening, with lows Monday night in the teens and highs Tuesday struggling back into the mid 20s to around 30.

A weak, quick-hitting clipper on the periphery of the larger scale closed low will bring low chances for snow showers to portions of the area mainly Wednesday night.

Even lower chances for precip come Friday night into early Saturday, mainly across southern portions of the area. Latest deterministic runs are keeping this precipitation well to our south, so would not be surprised to see the blend catch up in the next day or two and return a dry forecast here.

In general, expect temperatures to be much more seasonable for the final week of 2025 into the start of 2026, with at least one, perhaps two chances for light precipitation as we go through the week. Keep an eye on snow chances for New Year's Eve, particularly those planning to be on the roads that night.

AVIATION (18Z TAF Issuance)

Issued at 1244 PM EST Sun Dec 28 2025

Impacts:

- MVFR cigs expected through the TAF period with brief IFR at times - Line of showers and storms this evening, mainly from 23Z to 01Z - Southwest winds gusts peaking at 25-30kts this afternoon, veering to westerly tonight and increasing to 40kts - Flurries and light snow tomorrow, highest chances at LAF

Discussion:

MVFR conditions expected through the TAF period with cigs occasionally dropping to IFR at times through 04Z. A line of showers and storms is expected to move from west to east this evening from around 23Z to 01Z with a wind shift from the south to west in the aftermath of the storms. Winds will begin to gust to around 25kts after 20Z with gusts of 30-40kts in the aftermath of the storms through the night. The stronger winds will begin to relax towards the afternoon tomorrow with the potential of seeing flurries and light snow at times. Confidence in accumulating snow is low with best chances towards LAF.

IND WATCHES/WARNINGS/ADVISORIES

Wind Advisory from 6 PM this evening to 5 PM EST Monday for INZ021-028>031-035>049-051>057-060>065-067>072.