textproduct: Indianapolis

KEY MESSAGES

- Dense Fog Advisory overnight...through 11 AM Christmas Day

- Cloudy and dreary conditions for Christmas, turning warmer towards the weekend

- Transition back to much colder conditions next week

FORECAST UPDATE

Issued at 929 PM EST Wed Dec 24 2025

The premise of the forecast remains on track, with slight adjustments to account for latest trends and observations. A warm front continues to strengthen and push northward this evening. This has led to an increase in fog development over portions of central Illinois and southern Indiana. To the north of this front, weak mid level forcing is pushing eastward, resulting in some showers, especially where cloud decks still remain above 1500 feet due to some residual dry near surface air. This forcing will continue to create chances for showers within some elevated instability, the question remain on if there is enough saturation above the PBL to create showers vs drizzle. For now expected widespread drizzle, but near the warm front, moisture convergence may result in scattered convective showers at times through 09Z.

Stratus will lower quickly overnight as the The warm front stalls across central Indiana. The increase in subsidence following the mid level wave will further increase widespread fog development late tonight into the morning hours north of a Terre Haute to Rushville line. This is a bit further south that originally expected, and therefor the advisory for fog has been expanded southward.

Eventually, the front will move southward tomorrow morning, shifting the fog threat further south; however, there are some underlying mitigating factors creating less certainty in fog maintaining over southern Indiana tomorrow.

SHORT TERM (This evening through Thursday)

Issued at 231 PM EST Wed Dec 24 2025

Rest of Today and Tonight.

Main focus for the short term period will be tracking the drizzle/light rain tonight and the return of dense fog across central Indiana. As of early this afternoon, most of central Indiana is under mostly clear to partly cloudy skies, but this will rapidly begin to change towards the evening hours as higher clouds advect in from the west and a surge of moisture moves in from the southeast as winds gradually begin to ramp up. A few light showers will be possible late this afternoon and evening, mainly across southwestern Indiana associated with weak lift in the higher clouds but coverage will be fairly minimal with amounts generally no higher than a few hundredths of an inch.

Saturation near the surface is then expected towards midnight with drizzle becoming the predominant precipitation type as cloud bases drop to just a couple hundred feet. Widespread fog is expected tonight with dense fog likely along the warm front where winds will be near calm. Confidence on the exact location of the warm front remains somewhat low with the axis of long-lasting dense fog likely only a few counties from north to south. There shouldn't be much north to south movement with the front which could keep fog around for much of the night where it does form. After consulting with neighboring offices, we decided to go with a Dense Fog Advisory along and north of I-70 where confidence in the dense fog is greatest. A southerly expansion may be needed and will be looked at through the evening.

Thursday.

Other than some residual fog during the morning hours, quiet albeit dreary weather is expected for much of the day with light northeasterly winds in the aftermath of the exiting low. Southerly surface flow now looks to remain south of the forecast area which should keep the warmer 60s closer to the Ohio River. A fairly notable north to south temperature gradient is likely with a potential 15-20 degree swing between north central Indiana and the Ohio River. There may be some lingering drizzle, but with the flow becoming northerly, isentropic lift looks minimal with any forcing above the cloud layer.

LONG TERM (Thursday night through Wednesday)

Issued at 231 PM EST Wed Dec 24 2025

Christmas Night through Friday... A weak frontal boundary should remain positioned over the Ohio Valley, still looks to be oriented over Indiana and guidance has been wavering the last few days, but with the broad surface ridge displaced to the north this should keep the boundary just south of the Indy metro area through Christmas Night; however, the upper level jet structure still supports a progressive pattern setup. This indicates the boundary will quickly lift north and turn low-level flow southeasterly to southerly as it lifts north of Central IN.

Guidance still indicates a weak mid-lvl speed max to develop across the Central Plains early Fri, and appears to expand a precip footprint across the Ohio Valley Fri morning. But the caveat to lingering precip is that the surface low looks be lacking in a isallobaric gradient, indicating that low ceilings could develop midday with a persistent stratus deck under a light southerly moist flow. Guidance continues to indicate temps in the 60s, but if cloud cover is substantial this could be reduced due to the abundance of solar blocking and keep temps in the upr 50s.

Fri ngt into Sat... Mid-lvl height rises should slide east over Indiana, which will further reduce the pressure fields within the boundary layer. That indicates that we could have another period of some patchy fog, with mild temps given the lack of any cold air advection bleeding back into Indiana. Sat should feature another mild day with the boundary trying to sag south yet again, but the lack of a forcing mechanism in the upper levels should keep this feature displaced to the north.

Sun through Wed...Then heights continue to rise marginally late Sat ngt, setting Sun up to be another very mild day under stronger southerly flow as the upstream trough digs into the southwest CONUS. This will further amplify the downstream ridge over Ohio Valley. Ensembles continue to favor a system developing across the four- corners region Sun ejecting into the southern plains and possibly further developing with the increasing flow of warm/moist air from the west gulf. This should be a progressive setup and quickly push into the Ohio Valley by late Sun into Mon. Current indications are that this will be a mainly rain system but cold air advection will be pouring in from the northwest Mon, as the setup turns to a typical winter northwest flow. This then appears to be the main feature heading into the final days of the year with much more of a typical late Dec setup of cold temps and periodic chances for some snow showers.

AVIATION (06Z TAF Issuance)

Issued at 1219 AM EST Thu Dec 25 2025

Impacts:

- LIFR/VLIFR CIGs...IFR/LIFR VIS, overnight into Christmas morning - Improvement to IFR on Christmas at KLAF, and possibly KIND...with LIFR likely maintained at KHUF/KBMG through the TAF period

Discussion:

Mainly LIFR/VLIFR ceilings through dawn over central Indiana terminals as frontal boundary quietly crosses the region...amid light winds and increasing coverage of BR/DZ...which will also bring deteriorating visibility to mainly IFR/LIFR levels. Gradual improvement from north to south Christmas Day, with VIS leading, and CIGs hopefully climbing to IFR at KLAF/KIND during the afternoon, and MVFR possible at KLAF by 00Z Friday. KHUF/KBMG to potentially stay under LIFR stratus through the TAF period... with moderate confidence in LIFR CIG returning to KIND after 06Z Friday.

Light winds through the rest of the overnight will veer from southerly to 280-340 degrees by 12Z. Light breezes to continue veering Christmas Day as region receives southern edge of stronger polar high crossing Ontario/Great Lakes...with northeast winds at 19Z, and easterly flow by 00Z Friday. Slightly elevated winds to gust to 10-15KT by 06Z Friday.

IND WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory until 11 AM EST this morning for INZ021- 028>031-035>049-051>057.