textproduct: Indianapolis

KEY MESSAGES

- Winter Storm Warning for the I-74 Corridor. - Winter Weather Advisory most other 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, with higher amounts possible. - Arctic outbreak late Saturday to Monday morning. Low temperatures below zero...dangerous sub-zero wind chills down to -20F. - Moderation through mid-week to above normal temperatures...rain chances Wednesday night-Thursday

FORECAST UPDATE

Issued at 941 AM EST Sat Dec 13 2025

The forecast remains mostly on track with only a few minor adjustments made to POPs and temperatures. Latest KIND radar imagery and surface observations depict light snow is ongoing across the western half of central Indiana and as far east as the Indianapolis metro. Snowfall rates are light at this time due to weak overall forcing. However, stronger frontogenetical forcing currently over IL will overspread the area later this morning and into the afternoon. Look for snowfall rates to quickly pick up once the stronger forcing moves in. Expect road conditions to deteriorate quickly once these higher rates begin as well.

It appears ongoing light snow is mostly located near the I-70 corridor and south. Locations further north still have dewpoint depressions around 10F. Evaporative cooling should quickly saturate this pocket of drier air in the next hour or so with snow beginning near Lafayette by late morning and rapidly spreading eastward towards midday.

SHORT TERM (Today and tonight)

Issued at 346 AM EST Sat Dec 13 2025

Surface analysis early this morning shows deep and cold low pressure over northern Ontario. This was resulting in cyclonic flow across the Great Lakes and Indiana. A strong area of high pressure was found stretching from southern Central Canada sagging down across the plains to the middle Mississippi Valley. A weak surface ridge extended east from the high across KY. Aloft, strong and fast flow was in place, stretching from the Pacific northwest across the Rockies to KY and TN. A deep upper low was found over Ontario. An upper level short wave was found over the northern plains within the flow aloft, moving quickly southeast. This feature was producing some snow over MT and SD. This will be our main weather feature for today.

Today...

***Impactful snow through the day across most of Central Indiana***

***WINTER STORM WARNING for the I-74 corridor***

***WINTER WEATHER ADVISORY REMAINS IN EFFECT for much of the rest of CENTRAL INDIANA***

Models suggest the quick moving short wave over the northern plains will quickly push to Indiana and the Ohio Valley today, providing strong forcing upon arrival. Strong jet dynamics aloft will also be a key player today. Forcing should start arriving by mid day and persist through the afternoon before tapering off this evening. Forecast soundings show the arrival of a deeply saturated column this afternoon, persisting for 4-6 hours. During this time the dendritic growth zone of -10 to -20 remains fully saturated, favorable for snow. Mid levels in the models do a good job showing the arrival of the anticipated moisture just before 18Z and its departure just after 00Z. HRRR also suggests a swath of snow moving across Central Indiana from 16Z through 02Z. Thus many signals are present for this clipper snow event and confidence remains high. Highest snow totals should be along an I-74 corridor, impacting Lafayette, Crawfordsville. Indianapolis, Shelbyville, Rushville and New Castle. Overall amounts should range from 3 to 5 inches across the forecast area, but locally higher amounts, perhaps around 6 inches will be possible in the corridor listed above. Colder temperatures and the favorable DGZ, should lead to higher snow ratios. Thus have decided to issue WSW for that area.

The lighter snow and gusty winds around 15 mph may result in some blowing and drifting snow today and tonight, particularly on N-S roads in rural areas. Cold air advection will be ongoing today as the arctic air begins to arrive in the area. THis will result in falling temperatures through the day and high temperatures reached early in the day. This will result in wind chills in the single digits.

Tonight...

As the upper wave quickly departs this evening, best moisture and forcing will exit by 03Z. Pops may still be needed for a short window of 00Z-02Z, but the majority of the night will be dry and very cold as the arctic air mass associated with the advancing high pressure system arrives in Indiana. By 12Z Sunday, 850mb temps are suggested to reach around -18C. With new snow fall and clearing skies through the overnight period, temperatures will fall to the low single digits at most locations with values below zero at many spots. Ongoing cold weather advisory for this period will be on the mark.

LONG TERM (Sunday through Friday)

Issued at 346 AM EST Sat Dec 13 2025

Sunday through Monday...

An awaited transition to dry conditions will occur as the page turns into the long term, but at the expense of a potent early-season arctic outbreak...that will bring sub-zero mornings and dangerous wind chills Sunday into Monday morning. Amplified 1044 mb surface ridge crossing much of central North America, will be centered over the Middle Missouri River Valley early Sunday...shifting to the central Appalachians by the early Monday timeframe. Solid pressure gradient will continue 10-15 mph northwest winds gusting to 20 mph or so...with flow waning through late day and early evening hours as the center of the ridge nudges into the CWA from SW to NE. Winds to become light Sunday night as the arctic dome slides over the region, before stronger, now south-southwesterly, breezes resume going into Monday morning.

Temperatures will likely start in the negative single digits early Sunday under partly to mostly clear skies and amid the fresh, fluffy snowpack. Readings to struggle to climb during the day Sunday with single digits the rule most of the day...and likely even colder marks Sunday night per the light winds and moderate snow depth easily allowing radiative cooling processes. Isolated negative 10 or lower lows Sunday night are certainly possible over central/ northern counties. Moderate confidence in Monday's maximums reaching the 20s for most locations with the arctic high departing fast enough to bring substantial warm advection.

Wind chills will most likely be worst early Sunday given the lingering winds, with widespread negative 10 to negative 20 minimum values. Current Cold Weather Advisory in effect until 100 PM Sunday may potentially be extended or even upgraded to an Extreme Cold Warning...especially if the short term snowfall overperforms. Subzero wind chill values much of the day Sunday should actually improve into Sunday evening with the diminishing winds. Wind chills to fall yet again with increasing, warm-advective, return flow...which should unfortunately begin pre-dawn Monday...allowing negative 10 to negative 20 wind chills for consecutive nights. Wind chills to improve to 10 to 20 degrees by late Monday from noticeably higher temperatures.

Tuesday through Friday...

Moderate southerly breezes, courtesy of much-weaker surface high pressure lingering over the southeastern US...will maintain steady moderation through the mid-week. Afternoon highs climbing from the 30s Tuesday, to 40s Wednesday...will continue to moderate to around 50F for Thursday, with perhaps robust southerly gusts overcoming any cooling effects of scattered/numerous rain showers around the Wednesday Night-Thursday timeframe ahead of the next potent system's cold front. Overall zonal upper level pattern into the late week should prevent another arctic invasion, despite strong storm system crossing Ontario. Seasonably cool conditions expected as the long term period ends.

AVIATION (12Z TAF Issuance)

Issued at 533 AM EST Sat Dec 13 2025

Impacts:

- MVFR ceilings conditions becoming IFR this morning. - Widespread snow with deteriorating conditions near midday. - Poor flying conditions, IFR, with moderate to occasionally heavy snow Saturday afternoon. - A return to VFR after 140500Z

Discussion:

Radar Mosaics show an area of developing snow showers over IA and IL, quickly streaming SE toward Central Indiana. This snow will impact the TAF sites late this morning through the afternoon hours, providing IFR conditions with low cigs and poor visibility.

This feature is associated with the approach of an arctic cold front and a quick moving upper level clipper. Time heights and forecast soundings show deep saturation and moisture through the afternoon hours as the forcing passes. Winds around 10-15 mph will may allow for blowing and drifting snow, contributing to reduced visibilities.

Snow will end by 00Z-02Z and very cold air arrives on NW winds.

High pressure and subsidence will begin to build across the area after 140100Z...leading to clearing skies and a return to VFR by 140500Z.

IND WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until midnight EST tonight for INZ021- 031-041-042-060>063-070>072.

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

Winter Storm Warning until midnight EST tonight for INZ028>030- 035>040-043>049-051>057-064-065.