textproduct: Indianapolis

KEY MESSAGES

- Winter Storm Warning/Advisory for much of central Indiana

- Snow amounts of 4-7 inches in the Warning area, 1-4 in the Advisory

- Additional snow chances Monday night into early Tuesday, especially for south/southeast counties

- Wind chills at night...into the teens through Monday night...and then possibly single digits Tuesday night through Thursday night

MESOSCALE UPDATE

Issued at 908 AM EST Sat Nov 29 2025

Dynamical mesoscale environment unfolding across central Indiana this morning and over the next 90 minutes we will continue to see even more impressive atmospheric elements present themselves. Currently the WSR-88D shows a large footprint of reflectivity expanding northeast from Illinois, although aircraft data is still showing a large dry layer at the surface to around 3kft agl which is eroding the leading edge of the reflectivity as it approaches the Indy metro area. Further northwest there is an impressive band of precipitation and with the cold air at the surface the atmosphere is allowing full dendrites to reach the surface and rates are hovering around .5 inches per hour to near 1 inch. The bigger driver will be the strength of the warm air advection that is already pushing into Southwest Illinois and progged to reach Indiana by early afternoon.

As the atmosphere steadily saturates, this will cool temperatures down while dew points rise from the moisture surge. Some hi-res guidance continues to indicate a robust mid-lvl fgen band advancing northeast into west central Indiana, which will help to decrease the condensation pressure deficit that we presently still have. This will allow a burst of snowfall, potentially some moderate snow at the start, with large efficient dendrites quickly falling to the surface. Visibilities will additionally drop rapidly to around a half mile or at times lower than this.

We will do another mesoscale forecast discussion around 11 am est.

SHORT TERM (Today and tonight)

Issued at 300 AM EST Sat Nov 29 2025

A winter storm will bring first snow, then a mix of rain and snow to central Indiana through tonight. Snow will impact travel, especially across the northern forecast area, with the northwestern area seeing the worst impacts. No changes have been made to headlines with this update. Snowfall amounts have been lowered some in the south and tweaked elsewhere.

Isentropic lift will arrive by the start of the Today period, but it will have to overcome an initially very dry lower atmosphere. By noon, much of the northern three quarters of the area will have seen snow, so will have likely or higher PoPs there this morning. Lift will be weaker across the southeastern quarter, so will keep PoPs lower there.

This initial lift will move north this afternoon, with roughly the southern half seeing a relative lull during the early to mid afternoon hours. Forecast soundings show drier air returning to the southern half of the area during this time. Will lower PoPs there, but keep high PoPs north where forcing will continue. In the far south, temperatures may be able to warm enough that some rain might mix with any snow that falls during this time.

Later this afternoon into the early evening, another surge of lift will move into the entire area, ahead of the approaching frontal system and an increasing 850mb jet. An upper jet moving in will provide additional forcing. Will have high PoPs return to all areas. The precipitation will eliminate the drier low levels in the southern forecast area and allow temperatures to briefly cool again there. Mainly snow will be expected with this initial cooldown.

Warm advection ahead of the surface cold front will allow warmer air to move north and change precipitation to a rain/snow mix or just plain rain later during the evening into the early overnight. Colder and drier air will rush in during the remainder of the overnight, cooling things back down but also lowering precipitation chances.

The northern forecast area will see the longest period of mainly snow and will also see the longest period of forcing. Thus feel that the warning still looks good there. Delaware County looks to be even closer to the edge of conditions warranting a warning, but with uncertainty left it in the warning.

The I-70 corridor remains the area of most uncertainty and biggest bust potential. If drier air lingers there longer and/or warmer air gets to this area faster, amounts will be lower than expected. Even if this doesn't happen, there will likely be a tight gradient across counties in this area. For example, Marion County may see 4-5 inches in the far northwest but only around 2 inches southeast.

Across the south, amounts may be lower due to the drier air lingering this afternoon and warmer temperatures.

Winds will increase as the low pressure system to the northwest deepens, with gusts near 35 mph tonight.

Given that this is an early season event and a busy travel period, will leave the Warning and Advisory alone, even though some areas of these may not reach criteria. In addition, as temperatures fall back to below freezing tonight into Sunday, what has melted will refreeze, especially on untreated surfaces.

LONG TERM (Sunday through Friday)

Issued at 324 AM EST Sat Nov 29 2025

Unseasonable to anomalous cold to continue into first week of December...along with occasional chances of accumulating snow. 492 dm H500 Polar low displaced to Hudson Bay will lead quasi-split synoptic pattern over North America mid-latitudes...by directing steady flow of polar to arctic surface high pressure down Plains and across Midwest through the long term. Opportunities for primarily snow precipitation-type will range from lingering flurries/-SHSN on Sunday...another, quick-hitting, weather system Monday night into early Tuesday...and low certainty for possible light overrunning at the end of the period.

The short term's storm system will depart southeastern Michigan for southeastern Canada Sunday...while the elongated tail of its supporting short wave slides over the northern Midwest. Subtle surface reflection of this trough may be able to utilize dry adiabatic lapse rates below 925 mb to shake out a few snow showers and several flurries, especially from Lafayette to Rushville and points north/east, although little to no additional accumulation is expected.

Greater attention is now turning to increasing potential for light to moderate snowfall surrounding the Monday night timeframe...when a mid-level short wave embedded in the wintry flow quickly lifts from the Ozarks to Lake Erie...while interacting with a surface weakness expected to track across Kentucky. Resultant snow is expected Monday night, with an overnight burst most likely for far southern and southeastern counties where moderate snowfall is possible by early Tuesday. Subfreezing readings will promote slick surfaces where untreated. Lower confidence for late week precipitation chances where another overrunning type set-up could bring light snow or mixed precip into the CWA, although this may be difficult to realize as strong high pressure aligned just to our north may now allow more than clouds and virga.

Afternoon highs will most often be around 30F...while overnight minimums as high as the 15-25F range, also include 2-3 frigid nights through the mid- and perhaps late week where lows of 3-13F will be common amid the thicker snow pack north of the I-70 corridor. Wind chills will struggle to exceed 25 degrees and will consistently drop into the teens to single digits at night. The colder mid- to late week could easily support wind chills below zero Wednesday night and Thursday night for the region's northern half. Time should be limited outdoors, especially at night and when winds are elevated... utilizing multiple layers of clothing. The highest December daily record low temperature at Indianapolis is on 12/5 (8*F, 1886)...the current forecast low that morning is 10F.

AVIATION (12Z TAF Issuance)

Issued at 604 AM EST Sat Nov 29 2025

Impacts:

- Deteriorating conditions through the day in snow - Visibility will go IFR first into the afternoon followed by ceilings late afternoon into the evening - Worst prolonged conditions will be at KLAF. Best overall conditions at KBMG. - Winds veering through the day with gustiness increasing

Discussion:

Snow will have to moisten the lower atmosphere this morning, then visibility will drop first. Ceilings will eventually follow. Lower than IFR conditions will occur in heavier snow, with KLAF having the highest odds for these.

Rain will mix with the snow late today into this evening from south to north. After a cold front moves through overnight, precipitation will diminish with conditions improving to MVFR.

Winds will veer throughout the day then become westerly overnight. Gusts will increase this afternoon with gusts near 30kt possible overnight.

IND WATCHES/WARNINGS/ADVISORIES

Winter Storm Warning until 10 AM EST Sunday for INZ021-028>031- 035>041-043>047.

Winter Weather Advisory until 10 AM EST Sunday for INZ042-048- 049-051>057-060>065-067.