textproduct: Indianapolis

KEY MESSAGES

- Slick/icy spots possible Friday morning as temperatures drop quickly to well below freezing.

- Some snow showers at times late tonight into the early morning hours on Friday with minor accumulations possible.

- Wind chills into the single digits possible Friday morning.

- Warmer than normal temperatures in the 50s to lower 60s likely second half of Christmas week.

FORECAST UPDATE

Issued at 943 PM EST Thu Dec 18 2025

The area of rain behind the initial wind shift/cooler air boundary has persisted a bit longer than expected, but it is finally moving off to the east. Adjusted hourly PoPs to account for this.

Meanwhile, the true cold front with quickly falling temperatures behind it is in east central Illinois at the moment, moving steadily toward central Indiana. Not a lot of rain is along this boundary, so lowered PoPs some with this as it moves into the area.

Another round of gusty winds will occur with this boundary and will persist behind it with strong cold advection. Some gusts into the 30 to 40 mph range will occur, with most gusts on the lower half of that range.

During the overnight, lift from the upper trough and cyclonic flow (including isentropic lift and some frontogenetic forcing) will produce scattered to numerous snow showers. A few bands of snow may exceed 0.5 inches, but most areas should receive less than this.

Some of the latest guidance isn't quite as cold with low temperatures, especially south. However, seeing how fast readings are dropping upstream, decided to leave low temperatures alone for now. With the expected wind, wind chills in the single digits will be common by sunrise Friday.

The combination of minor snow accumulations and residual water freezing on untreated surfaces will lead to slick areas on roads by sunrise. Will issue a Special Weather Statement for this.

SHORT TERM (This evening through Friday)

Issued at 255 PM EST Thu Dec 18 2025

A strong storm system moving through the region will continue to support multiple weather hazards through the overnight. A strongly forced heavy rain squall line along a cold front has had a history of producing wind gusts over 50 mph in central and southern Illinois the last few hours. In addition, gradient wind gusts from 30-40 mph have been prevalent across the forecast area the last few hours. Both the gradient wind gusts and the precip enhanced wind gusts will support the need for a wind advisory until the early evening hours (01Z) before the cold front moves east of the area. The threat for thunderstorms remain very isolated given poor lapse rates and negligible MUCAPE in the sub -20C layer. SPC has the far SW part of the forecast area in a marginal risk for severe wind gusts.

The forecast then turns to the sharply colder temperatures moving into the region from the NW overnight. 2M temp consensus shows readings reaching 32F by 04Z in the far NW part of the forecast area to 08Z in the far SE. Low temperatures by 12Z Friday ranging from 15- 20 F north to 20-25 F in the south from the blended guidance look reasonable. The quick fall in temperatures with recent QPE (0.25 to 0.75 inch per MRMS) and additional QPF of 0.30 to 0.6 inch, should support some ponding and residual water on area roads well into the night. Therefore the threat for a flash freeze later remains a concern for later tonight. In addition, the thermodynamic and large scale forcing support a classic "ground effect" snow shower event for central Indiana overnight. The transition to snow will occur roughly the same time as mentioned for the 32 F line. Steep low level lapse rates up to 850mb, subtle low level vertical motion, (orographic lift from the MS valley) and the presence of mid level PVA all support these snow showers. Accums up to 1 inch look possible and most likely these snow showers will be in several parallel bands oriented along the mean shear vector in the BL.

Snow showers should diminish from west to east between 09-13Z Friday as mid level height rises and a strengthening low level inversion build in to the region in the wake of the shortwave trough axis. Skies will gradually clear by afternoon from west to east as drier air/greater subsidence move into the region. Have bumped up wind gusts through the night to near 30-35 mph lasting into the mid morning hours following a blend of the HRRR and other CAMS thanks to the steep lapse rates and strong CAA. These wind gusts will abate to less than 20 mph by late afternoon as surface high pressure ridge builds into Indiana from the MS valley.

LONG TERM (Friday night through Thursday)

Issued at 255 PM EST Thu Dec 18 2025

Friday night through Sunday...

Mostly quiet weather is expected early in the period with surface high pressure remaining in control. A low pressure system and parent trough will move through the Great Lakes Region late Saturday pushing a cold front across central Indiana. Precipitation is unlikely due to forcing remaining north of Indiana, but increasing warm advection should moderate temperatures considerably. The colder airmass settling in early Friday should generally keep highs in the mid 20s to low 30s with warmer highs in the mid 40s to low 50s by Saturday.

A tightening MSLP gradient and diurnal mixing may promote wind gusts between 25-35 mph on Saturday. Cooler air then settles back in Saturday night into Sunday. Expect lows in the 20s overnight while highs Sunday only reach the 30s under persistent CAA.

Monday onward...

Model guidance depicts amplifying ridging aloft next week with subtle waves moving across the northern periphery of the ridging. These subtle waves along with increasing warm air advection supports low chances for precipitation at times. Look for highs in the 40s to warm into the 50s Tuesday and eventually widespread 60s by Christmas. Predominately rain is expected due to the significant warm up.

There are slight hints a weak wave could move in during the day Monday with the potential for light snow before temperatures warm up enough. This solution is an outlier and appears unlikely as most guidance shows the weak impulse moving in later when temperatures are above freezing, but will continue to monitor trends for any changes.

AVIATION (06Z TAF Issuance)

Issued at 1237 AM EST Fri Dec 19 2025

Impacts:

- Snow showers through 12z, brief reductions in visibility to IFR possible.

- Gusts up to around 30kt at times into the morning hours, gradually diminishing after 18z.

- MVFR ceilings persisting into the afternoon.

Discussion:

A strong arctic front passed through central Indiana around 05z, and all rain has transitioned to snow. Snow showers are expected to continue on and off through 12z, with brief reduction in visibility possible to as low as 1-2 miles.

MVFR stratocumulus will likely persist into the afternoon hours as well, gradually retreating from south to north. Stratus should completely lift northward by 03z as winds become southeasterly.

Before that, west-northwesterly winds between 10-20kt gusting to 30kt are expected this morning into the early afternoon.

IND WATCHES/WARNINGS/ADVISORIES

None.