textproduct: Indianapolis

KEY MESSAGES

- Light rain and drizzle expected tonight into Tuesday, patchy fog possible as well.

- Moderating pattern into the middle of the week with unseasonably mild conditions expected Wednesday-Friday

- Near record high temperatures in the 60s possible on Christmas Day

FORECAST UPDATE

Issued at 952 AM EST Mon Dec 22 2025

No major changes needed to the forecast with conditions evolving as expected. Temperatures continue their slow rise across central Indiana with most areas now at or above freezing. Once temperatures rise above freezing, the next time they are expected to fall back below won't be until either Sunday or Monday morning. Clouds continue to stream in from the northwest with most areas having at least some thin cirrus outside of the far southwestern counties.

There may be a brief window of clearing this afternoon before additional clouds associated with the expected light rain arrive this evening into tonight, but otherwise mostly cloudy skies are expected through tomorrow morning. With the fairly strong southeasterly surface flow and expected clearing, temperatures should be able to rise into the upper 40s to low 50s across central Indiana

SHORT TERM (Today and tonight)

Issued at 318 AM EST Mon Dec 22 2025

Synoptic analysis reveals broad ridging extending across most of the CONUS, with troughing over the far PacNW and NE. The primary ridge axis is across the central Plains. A progressive jet remains well to our north, roughly along the US Canada border. A weak shortwave is riding this flow and will help initiate surface cyclogenesis this morning over the northern Plains. The resulting surface low, while weak, will then track northeastward over the Great Lakes.

The approaching system should generate a modest low-level jet (30- 40kt at 925mb) later this morning, which will promote moisture advection northward. By this afternoon (21z-00z), a thick shield of low-level stratus is expected to arrive. Despite moisture advection, it is not deep and there is limited forcing aloft. Our primary source of forcing is isentropic ascent associated with the modest LLJ. Precipitation is therefore limited to light rain/sprinkles or drizzle. Dreary conditions should persist tonight into Tuesday before the LLJ drifts eastward with the departing system.

Patchy fog is possible tonight into Tuesday as well, given the high level of boundary layer saturation expected. However, brisk southerly winds and the depth of the stratus layer should promote drizzle rather than fog. However, some patchy fog cannot be ruled out.

In terms of temperatures, we'll see our coldest readings this morning before mid/high cloud cover rolls in. Warm air advection today should lead to highs near 50. Clouds, wind, and continued warm air advection will keep temps mild overnight with lows in the 40s. With the warming trend comes potentially breezy conditions, especially this afternoon. Southerly wind gusts between 20 to 30 mph are possible at times.

LONG TERM (Tuesday through Sunday)

Issued at 318 AM EST Mon Dec 22 2025

Tuesday through Christmas Day...

Broad subtropical upper ridge to build north over much of CONUS, with axis positioned along the Plains, maintaining 576 1000-500 mb layer thickness over central Indiana into the day Thursday. Corresponding surface pattern to feature weak high pressure over Deep South and into the Gulf...and often-weak frontal boundary, quietly crossing region Tuesday...before meandering from Tennessee Valley early Wednesday, to probably back north of the CWA by late Christmas Day.

Main forecast concerns through the mid-week will focus around the combination of moisture advection under a generally impressive inversion below 850mb...which will support widespread low stratus, and potential fog. Visibility reductions may be greatest Tuesday night when diminishing breezes and several hours of mostly clear skies are expected.

Temperatures trends and spatial distribution of anomalous to near- record readings have lowest confidence on Christmas Day given model divergence on northward warm front progress. Certainty is lowest for central/northern zones, yet still a good chance that low 60s make it to most of the region.

Otherwise the Wednesday to early Christmas Day timeframe will bring at least low chances for rain showers around more organized rain coverage possible around the Wednesday night period when a small disturbance embedded in the upper ridge passes over the region, although low certainty on rainfall amounts for any particular location.

Friday through Sunday...

Return to a more zonal upper pattern will oversee steady decrease in temperatures back to near normal levels by the end of the long term. Potentially another very mild day Friday if boundary/any passing open wave surface low pressure continues to our north. Stronger transition expected by the end of the weekend as strengthening cold frontal zone crosses the Midwest in conjunction with southern portion of amplified polar high pressure expected to cross the southern Plains. The normal max/min for Indianapolis for the long term is 38/24.

AVIATION (12Z TAF Issuance)

Issued at 624 AM EST Mon Dec 22 2025

Impacts:

- Light southerly winds increasing today with gusts to 20 kts

- MVFR stratus arriving from the south late this afternoon and evening

- Light rain, drizzle, and potential IFR condition possible tonight

Discussion:

Light and variable winds persist for a few more hours before winds become southeasterly around sunrise. By this afternoon a 25-35 kt southwesterly low level jet moves overhead. Gusts up to 20 kts are possible into the evening hours as stronger gusts mix down to the surface. Winds should gradually become more southerly with time.

Mid/high-level cloud cover is increasing ahead of an approaching system over the Plains. Strong moisture advection associated with this system will bring MVFR stratus northward near between 20z-00z, but confidence is low in how quickly cigs may drop before 00z.

After 00z, guidance shows stratus rapidly fill in allowing all terminals to become MVFR or lower. There is a good signal for rain showers followed by drizzle at times Monday night into Tuesday, so we will introduce it into the TAFs along with minor reductions in visibility. Some guidance depicts further reductions, potentially into IFR territory mainly after 06z.

Some improvement is expected Tuesday morning.

IND WATCHES/WARNINGS/ADVISORIES

None.