textproduct: Indianapolis

KEY MESSAGES

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

- Breezy conditions develop Monday with winds gusts to 25 mph

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

SHORT TERM (This evening through Monday)

Issued at 200 PM EST Sun Dec 21 2025

Atmospheric setup this afternoon features a broad surface ridge, with the axis drifting over Central Indiana. This will allow winds to briefly go calm, unfortunately the upper level flow remains transient and progressive. Surface ridge will quickly depart to the east late tonight, and in its wake will be a robust return flow from the south/southwest that will usher in much warmer air and moisture back into the Ohio Valley as strong isentropic ascent to parcels will rapidly lift north from the gulf coast.

Tonight the surface ridge pushes east, allowing the pressure gradient to return on the backside. This will allow winds to turn southerly and increase, along with an end to the clear skies as moisture quickly arrives overnight in the form of increased clouds. At sunset expect a brief, somewhat steep, radiation of surface temps to occur under optimal conditions. Temps will likely settle into the mid/upr 20s before they steady or possibly start to rise around daybreak Monday.

Monday/Monday Night... The main feature of this period will be the warm air advection. There will be a weak surface pressure low that will skirt the Great Lakes but this will help to lift a warm frontal boundary further north. 850mb thermal ridge coupled with a solid moisture push from the south as a modest low-level jet of 30-40kts will help to expand north moisture. Highs Mon have been nudged up a couple of degrees into the upper 40s and very possibly around 50 for portions of Central Indiana. Given the abundance of moisture throughout the profile Mon ngt, and continued south/southwesterly flow and a beefy thermal ridge in the low-levels, temps will likely not fall much at all Mon ngt.

LONG TERM (Monday night through Sunday)

Issued at 200 PM EST Sun Dec 21 2025

Broad warm air sector will encompass all of Central Indiana with a broad low-amplitude system impacts the region. Temps as a result will easily rise into the 50s, despite the mostly cloudy sky cover. There is a very weak moisture starved front that will make an attempt to sag south into the northern counties Tue, although expect the southerly flow to prevail and keep this feature to the north. As we push into Christmas Eve the thermal ridge intensifies. Strong southerly breezes will push dew points into the upper 40s to mid 50s, which is exceptionally high for late Dec across Indiana. This should allow some scattered showers to develop across the area, with the couple strong ascending isentropic lift to parcels. But again the main feature worth noting will be the surface temps that will likely be around 60.

Christmas Day through the day after... Ensembles continue to prog 2 to 3 standard deviations above normal for the 850mb thermal ridge that will reside overhead. The center of this ribbon of warm air is progged to be over the Ohio Valley, which should further support temps easily pushing into the mid 60s on Christmas Day. It is conceivable that some locations in southern Indiana could touch 70 degrees. Then heading into Friday not much will change, but there is some relaxing to the thermal ridge overhead so likely going to see temps just hold in the upper 50s to lower 60s. Deep moisture remains locked, but with a lack in upper-level forcing any precipitation that develops should be manageable. Guidance still indicating the upper level pattern will begin to flatten to more of a transient or zonal setup, as a frontal boundary approaches late Fri. Timing for this boundary could be a bit sooner, as the zonal flow indications amongst ensemble members has been indicating more spread and this is an indicator in reduced confidence in timing.

Saturday through Sunday...Seasonable airmass returns to the region for the weekend, which should bring temps back into the upper 30s to 40s, with a periodic chance of precipitation. Nothing significant at the moment, but some ensemble members are hinting that a stronger arctic ridge of high pressure may attempt to build in again from the northwest from the Canadian Rockies.

AVIATION (18Z TAF Issuance)

Issued at 200 PM EST Sun Dec 21 2025

Impacts:

- Lgt Variable Winds turning south

- MVFR stratus arriving Monday afternoon

Discussion:

Light and variable winds persist through tonight, before winds become southeasterly as the high passes eastward late tonight.

Mid/high-level cloud cover should gradually increase tonight ahead of an approaching storm system. Strong moisture advection associated with this system will bring MVFR stratus northward near the end of the TAF period. Additionally, light rain or drizzle is possible later Monday evening into Tuesday.

IND WATCHES/WARNINGS/ADVISORIES

None.