textproduct: Indianapolis

KEY MESSAGES

- Winter Weather Advisory most areas Saturday into Saturday evening. Cold Weather Advisory all areas Sunday morning.

- Accumulating snowfall will occur midday Saturday into Saturday evening. Three to 5 inch accumulations will be common.

- Arctic outbreak late Saturday to Monday morning. Low temperatures near or below zero and dangerous sub-zero wind chills down to -20F.

- Temperatures will warm to above normal by middle of next week, with most snow melted by Thursday.

SHORT TERM (This evening through Saturday)

Issued at 305 PM EST Fri Dec 12 2025

Rest of This Afternoon...

Some partial clearing will persist for a while, but do expect the clouds to continue to gradually fill back in.

Tonight...

Clouds will help keep temperatures from falling too much for the night. A cold front will enter the northwest forecast area late tonight, potentially dropping temperatures there into the teens by around 12Z. Otherwise, lows in the 20s can be expected.

Saturday...

The cold front will continue to sink south through the day, gradually lowering temperatures overall. This front may have enough forcing for a few snow showers in the northern forecast area in the morning. However, the main forcing for this event will arrive mid to late morning into early afternoon from the west.

Forcing from an upper trough and the right rear quadrant of an upper jet will interact with the moisture across the area to produce snow. In addition, there will be some frontogenetical forcing and negative EPV above this forcing. This will lead to some more intense bands of snow. Will have to also watch out for larger dendritic growth zones.

There looks to be a sharp cutoff to the forcing across the far southwestern forecast area.

Will go high PoPs most areas Saturday, mainly during the afternoon, except for the far southwest where only chance to likely PoPs will be needed due to the sharp cutoff.

Specific amounts will be a bit tricky for a few reasons. First is that the banding will produce higher amounts in narrow bands that can cause variability across even within a county. Second is the sharp cutoff to the south. If that shifts, either direction, amounts could change more there than elsewhere. Finally, temperatures will be falling through the day, increasing the snow ratio. Colder temperatures early could lead to higher snow amounts due to higher ratios.

Given all of the above, feel that 3 to 5 inches is the most likely range of amounts for the majority of central Indiana. Areas near Seymour may be more of a 1-3 or 2-4 situation, while the far southwest will be a gradient of less than 1 to around 2. Went with a Winter Weather Advisory for all but the far southwest 3 counties given these amounts. Locally higher amounts around 6 inches are definitely possible in the banded heavier snowfall.

Winds will be higher than the last system, and the snow will become less dense, making for the potential for some minor blowing snow.

Saturday night...

Snow will likely be ongoing at the start of the period across the southeast forecast area, but this will quickly end as forcing exits and high pressure builds in. Temperatures will fall, reaching below zero for the northwest half or so of the area with near zero elsewhere.

Winds will remain up with the surface high to the northwest, so wind chills will fall to colder than -10 for the vast majority of the area during the night. These cold wind chills will last into Sunday. Thus, have also issued a Cold Weather Advisory from midnight Sunday to 1 PM Sunday for all areas.

LONG TERM (Saturday night through Friday)

Issued at 305 PM EST Fri Dec 12 2025

After a cold and mostly clear day Sunday, another night of frigid temperatures is expected Sunday night as the 1040 mb high moves across and just east of the forecast area. Although winds will be much lighter than Saturday night, actual air temperatures are expected to be solidly in the 0 to -10F range across the area. Wind chills look to be anywhere from -8 to -15 degrees late Sunday night into Monday morning. Later forecasts may need the inclusion of another cold weather advisory for Sunday night/early Monday if wind chills look to be colder than -15 degrees.

In the wake of this weekend storm system a major upper level pattern change will occur for the rest of the extended forecast thanks to increasing waa, zonal flow and a deepening long wave trough off along the west coast. 850 mb temps rise from -10C on Sunday to +8C on Tuesday. The complicating factor for how quickly surface high temperatures warm along will be the potential affects of the snow melt /moistening and cool remaining near surface layer/ beneath a warming aloft. As a result, the current forecast highs for Wednesday- Thursday may be quite over inflated. In addition, patchy dense fog may become a factor during this period, especially in the initial strongest waa period. Later forecasts will hopefully have more sensible data (including snow pack depth) which will be a contributing factor to the duration of snow melt and delay of warmer temperatures.

By Thursday there is agreement of an approaching shortwave and precipitation back in the forecast across central Indiana. However, the degree of precip amounts is still highly in question as variability exists in the strength of this system given the spread of the GEFS/Euro ensemble members. In general near to slightly below temperatures are expected Friday ahead of an associated cold front.

In the wake of this shortwave the zonal pattern will reestablish itself with waa across the central and much of the eastern conus ahead of the longwave trough off the west coast. The result will be temperatures warming back above normal by next weekend. Just beyond the extended, there is a signal for increasing longwave troughing over eastern canada. This pattern favors shallow arctic air masses may develop south setting the stage for one of more weak freezing precip events with any shortwave trough energy emerging out of the west. Stay tuned.

AVIATION (18Z TAF Issuance)

Issued at 1151 AM EST Fri Dec 12 2025

Impacts:

- Predominant MVFR ceilings, but some variability this afternoon. - Widespread snow with deteriorating conditions after 131600Z

Discussion:

Holes have developed in the clouds across central Indiana today allowing some areas to become VFR. Meanwhile, patchy IFR ceilings remain in otherwise MVFR areas.

Moisture will linger through tonight, especially in the MVFR category, so will continue with predominant MVFR ceilings. However, given the above, will likely see some bouncing through categories this afternoon.

Patchy light snow is possible after 12Z Saturday, but widespread snow shouldn't arrive until after 16Z or so. Conditions will deteriorate as the snow continues into the afternoon.

IND WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 11 AM Saturday to midnight EST Saturday night for INZ021-028>031-035>049-051>057-060>065- 070>072.

Cold Weather Advisory from midnight Saturday night to 1 PM EST Sunday for INZ021-028>031-035>049-051>057-060>065-067>072.