textproduct: Indianapolis

KEY MESSAGES

- Fog development expected again tonight; greatest coverage across the north where there is increasing potential for dense fog

- Drizzle possible at times overnight with increasing coverage of showers late tonight into Friday

- Additional rainfall early next week with much cooler weather likely post-Thanksgiving

FORECAST UPDATE

Issued at 921 PM EST Thu Nov 20 2025

Main concern overnight will be the potential for fog development. This is primarily expected to occur north of I-70 where some mid level subsidence should push the stratus layer towards the surface. The more uncertain caveat will be just how dense this fog will get. Most areas north of I-70 should fall beneath 2SM, but there could be a corridor with dense fog (1/2SM or less). Currently this is expected over the upper Wabash Valley, but trends will have to be watched closely for points east of this region.

South of I-70, onset of rainshowers has been mostly delayed until the morning hours outstay of some isolated chances along a push of isentropic lift between 04-08Z.

SHORT TERM (This evening through Friday)

Issued at 249 PM EST Thu Nov 20 2025

Continued dreary conditions can be expected through the period as a persistent subsidence inversion aloft and warm air advection beneath it allows a low-level stratus deck to remain in place. Latest observations show ceilings and visibilities have improved gradually through the day as temperatures have slowly warmed. Unfortunately, this improvement will only be short-lived as ceilings and visibilities drop again overnight.

Latest guidance has trended drier overnight especially across the northern half of the area. Forecast soundings show the subsidence inversion strengthening over the north slightly with winds becoming very light or even calm at times. This and very small dewpoint depressions will quickly promote fog development into the overnight, potentially dense. Patchy drizzle is also possible thanks to marginal forcing. Guidance shows subsidence slowly increasing aloft overnight across the south as well. However, greater PBL moisture and slightly stronger forcing supports better chances for drizzle and the development of light showers. The higher chances for light precipitation over southern counties leads to lower confidence in coverage or duration of fog overnight.

Model guidance depicts the aforementioned subsidence inversion weakening with increasing isentropic ascent during the day Friday. This will lead to greater coverage of showers as the day goes on. Showers should help clear out fog through the morning. Cannot rule out fog lingering through midday across the north if showers move in later than expected. Blended guidance has been far too warm with the stratus deck overhead which has limited the diurnal temperature swing significantly. High temperatures today and tomorrow were trended lower than the NBM. Look for lows to generally range from the mid 40s to near 50F tonight while highs Friday mostly remain in the low 50s.

LONG TERM (Friday night through Thursday)

Issued at 249 PM EST Thu Nov 20 2025

Upper-level analysis shows a progressive split flow jet pattern over the CONUS. Flow tends to split over the west coast before converging again over the Midwest. This broad upper-level convergence, in tandem with surface high pressure pushing southward, will lead to broad subsidence Friday night into Saturday. Model trends have shown this subsident atmosphere edging southward, and have shown less rainfall compared to previous runs. We will trim PoPs a bit across our north while maintaining likely to categorical PoPs from Indy southward. We lowered total expected rainfall amounts as well, especially further north. Further reductions may be needed.

The system responsible for Friday's rain will depart eastward on Saturday. Surface high pressure arrives along with a dry continental polar air mass from the north. With a drying trend shown in guidance it now appears likely that we'll finally see some sunshine beginning on Saturday. Clear to partly cloudy skies should then continue through the weekend. Larger diurnal temperature swings are expected due to clearing skies, with highs in the 50s/low 60s and lows in the 30s. Patchy overnight fog is possible at times this weekend due to recent rainfall and ideal radiative cooling during the overnights.

Quiet weather continues into the new week, but is not expected to last long. A storm system, currently over southern California, looks to eject eastward out of the Rockies on Monday. Guidance shows this system remaining quite weak while potentially merging with a system moving eastward over the US/Canadian border. Guidances diverges at this point, with various models handling the potential interaction differently. Regardless, rain appears likely as the southern system moves northeastward on Tuesday. How much rainfall and exact timing will come down to how the interaction with the northern stream evolves.

A trend towards colder weather appears increasingly likely late in the week or next weekend. The aforementioned split flow pattern looks to consolidate into a single stream with broad troughing over the central and eastern US. Timing and magnitude of the initial push of cold air may again depend on the interaction of the early-week storm systems. A stronger resultant low may allow for a quicker/stronger push of cold air southward, and vice versa.

Day 8-14: Taking a peek towards the end of the month / early December. Ensemble guidance hints at continued troughing over the northern US with repeated shots of arctic air (whether these make it to Indiana is unknown as of now). Additionally, ensemble guidance hints at troughing shifting westward which may allow for a more active storm track over the Midwestern US.

AVIATION (00Z TAF Issuance)

Issued at 640 PM EST Thu Nov 20 2025

Impacts:

- Widespread IFR/LIFR conditions overnight

- Drizzle or light showers moving in tonight into Friday morning

Discussion:

Widespread low stratus and fog continue across the area with IFR/LIFR conditions. Some light drizzle has been reported at times as well.

Drizzle or light showers will move in during the overnight hours with visibilities deteriorating to IFR or worse. The lowest visibilities are expected at KLAF and KIND with the emergence of some 1/2-2SM MIFG.

Widespread rain will arrive tomorrow, with greatest coverage at KBMG. Tempo groups or shorter from groups may be more appropriate for KIND, KHUF and KLAF tomorrow as confidence increases in rainfall timing.

IND WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory until 10 AM EST Friday for INZ021-028>030- 035>037-043-044.