textproduct: Indianapolis

KEY MESSAGES

- Accumulating snow tonight into tomorrow morning with a narrow swath of 2-5 inches over the southwest half of central Indiana

- Second round of accumulating snowfall Saturday midday to evening

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

MESOSCALE UPDATE

Issued at 937 PM EST Thu Dec 11 2025

Snow has gradually expanded northeast across the forecast area through the evening and was now at 0230Z approaching the Lafayette and Indy metro areas. Moderate to occasionally heavy snow continued across the southwest half of central Indiana and already had seen accums around 2 inches in spots in the lower Wabash Valley.

The deformation band has set up further southwest than model guidance suggested even as late as this morning and as a result the orientation of the band of heaviest snowfall has gradually shifted S/SW all day. Now as the clipper has moved in...feel confident that the swath of heaviest snowfall will align between Terre Haute and Sullivan...Bloomington and Bedford southeast through Seymour. Still feel that 3 to 5 inches will be common in this zone but the wild card will be exactly where the pivot point to the surface wave takes place. This has the potential to prolong the heavier snow rates for a short time and nudge snow amounts up even a bit more...potentially across far southern portions of the forecast area extending southeast into north central Kentucky.

Most of the updates this evening though have focused on tightening the snowfall gradient on the northeast flank where drier air in the 850-700mb layer has delayed the onset of the snow this evening and is likely to mitigate snowfall rates as well into the overnight. Largely expect snowfall amounts at 2 inches or less northeast of I- 74 with amounts dropping off rapidly to the northeast. Far northeast counties may only see a dusting to couple of tenths of an inch of snow at this point. For the Indy metro...have dropped to a 1 to 3 inch range with the amounts above 2 inches confined to the far southern/southwest suburbs.

Zone and grid updates out.

SHORT TERM (This evening through Friday)

Issued at 308 PM EST Thu Dec 11 2025

A round of accumulating snow is in the forecast tonight through tomorrow morning for portions of Central and South Central Indiana.

A clipper system developing on the lee side of the Rockies traverses eastward across the Plains tonight then just south of the state by the morning hours. Aloft, a 140 kt jet streak from British Columbia to Indiana has induced surface cyclogenesis on the lee side of the Rockies in Wyoming and Colorado. The low is expected to track along a tight low level thermal gradient separating an incoming arctic airmass to the north and a very warm airmass over the Plains. Today's guidance has continued the trend of shifting the track of the low southward about 50 miles, along with the axis of heaviest precipitation. The forecast has been adjusted to account for the southward shift.

By tonight, a 140 kt jet streak overhead, places Central and Southern Indiana within the right entrance region, in an area of enhanced lift. Latest guidance places the best low to mid level frontogenetical forcing along and southwest of the I-74 corridor in the 03z-09z timeframe tonight. Despite a lack of strong moisture advection ahead of the system and little to no Gulf moisture interaction, frontogenesis and lift within the exit region of the jet will work together to squeeze out what moisture is available and lead to isolated areas of higher snow amounts. Best forcing for ascent within the dendritic growth zone occur from around 00z-08z, before mid level dry air work its way in. This is the timeframe where snow to liquid ratios will be highest (drier snow). After the 2-4am timeframe, the low level thermal profile becomes marginal for dendritic growth, so expect lower snow to liquid ratios on the back half of the snow event and as things taper off Friday morning.

With all this said, while it is not a perfect scenario for efficient snowfall production and higher accumulations, enough parameters are coming together to support a period of accumulating snow tonight across portions of Central and South Central Indiana. With the southward shift in all guidance, the narrow axis of highest snowfall amounts look to be south of the I-74 corridor with 3-5" possible from Terre Haute to Bloomington to Seymour. Isolated 6" amounts are expected within the axis of higher snowfall, but confidence is not high enough in widespread 5-6+ inch amounts to warrant upgrading the advisory. Confidence is increasing in amounts closer to 1-3 inches for the Indianapolis metro and counties along I-74, with a sharper cut off as one heads northward. Will need to watch southwestern Indiana overnight tonight as the low may track overhead and push enough low level "warm" air in to raise temperatures above freezing in the vicinity of Knox, Martin, and Daviess counties. If this happens, a changeover to rain may occur briefly, keeping snow amounts on the lower end of the forecast ranges. Lowest confidence areas are on the edges of the snow band, just north of Indianapolis and on the far southern edge of the system as any wobble in the axis of heavy snow, even by 25 miles, can mean the difference between one inch of snow and several.

For timing, isolated snow showers have been ongoing across Indiana today however steadier can be seen on radar already beginning across Illinois. By 5 PM, light snow should be beginning along the IL/IN state line, then advance eastward after sunset. The best dynamics for heavy snow align from around 8PM to 3AM, then lighter snow expected through the rest of the morning hours before tapering off from west to east. No changes made to the Winter Weather Advisory. Expecting widespread travel impacts for the Friday morning commute, then improving conditions midday Friday as temperatures rise to or above freezing in many locations.

LONG TERM (Friday night through Thursday)

Issued at 308 PM EST Thu Dec 11 2025

More accumulating snow followed by dangerously cold wind chills can be expected Saturday into Sunday.

Another round of upper energy along with incoming Arctic air on Saturday will provide forcing. The area will be in the right rear quadrant of an upper jet will also add forcing, and there is some potential for frontogenetical forcing. Moisture will still be around, and the incoming Arctic air will help squeeze out moisture as well.

Thus, expect another accumulating snowfall Saturday into Saturday evening. Current thinking is another 2 to 4 inches for much of the area. However, guidance is still differing on the location of the axis of higher totals, with the NAM noticeably north of most other solutions. Amounts will also be harder to pin down for some areas as the snow ratio increases with colder air filtering in.

After the forcing ends and snow exits, Arctic high pressure will increase its influence on the area, bringing drier air and decreasing clouds. Winds will remain up through Sunday morning, so radiational cooling won't be strong. However, the airmass will be cold enough to bring subzero temperatures to much of the area, with near zero readings elsewhere. Wind chills will approach -20, so cold headlines will likely become necessary.

Sunday will be cold and dry as the high moves in. Highs will generally be in the single digits, and Indy's record low maximum temperature of 9 degrees will be in jeopardy. Winds will diminish, but subzero wind chills will continue.

Sunday night looks to be the coldest night with mostly clear skies, light winds, and the fresh snow cover from Saturday. Lows will likely be below zero most areas, with the potential for near -10 readings at a few locations. Minimums may occur early in the overnight as winds do increase a bit later in the night. With lighter winds, wind chills won't be quite as cold as the previous night, but still bitterly cold.

The high pressure will move off to the southeast for early next week, allowing warmer air to return. Mid-week upper flow will be near zonal. This will result in highs returning to the 30s Tuesday and to the 40s for Wednesday and Thursday.

A system could bring some rain later Wednesday into Thursday, but details on timing and strength still need to be determined.

AVIATION (00Z TAF Issuance)

Issued at 541 PM EST Thu Dec 11 2025

Impacts:

- Snow arrives with rapidly deteriorating conditions early this evening, especially at KBMG and KHUF - Sub-IFR conditions expected from late evening through early Friday - Snow ending early Friday morning - MVFR ceilings linger all day Friday

Discussion:

Widespread snow will expand into the region from the west this evening with conditions rapidly deteriorating as the evening progresses...especially at KBMG and KHUF. Greatest impacts are expected are expected at those two terminals with brief periods of heavy snow and 1/4SM visibilities in the 03-08Z timeframe. KIND and KLAF will likely experience a 2-4 hour period of moderate snow overnight as well. Conditions improve slowly in the predawn hours and through daybreak from northwest to southeast as snowfall becomes light and ends. Ceilings will slowly improve back to 1500-2000ft by the afternoon but hold firm through the end of the forecast period.

Light E/SE winds are expected into Friday morning...then shifting to northwest at less than 10kts in the afternoon.

IND WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 10 AM EST Friday for INZ028>030- 035>037-039-043>048-051>057-060>065-067>072.