textproduct: Indianapolis

KEY MESSAGES

- Light snow likely late tonight into early Wednesday.

- Up to an inch of snow possible. Possible impacts to the Wednesday morning commute on untreated roads.

- Light rain chances on Thursday morning. - Above normal temperatures return late week with highs near 70 expected Friday and near 80 possible on Saturday.

SHORT TERM (This evening through Wednesday)

Issued at 321 PM EDT Tue Mar 17 2026

Rest of the Afternoon...

Have adjusted temps downward thanks to persistent clouds, with highs expected to remain in the 20s across central Indiana. These are the coldest temperatures for St. Patrick's Day since 1941 when the high temperature at Indianapolis was only 20 degrees! Accumulating snow has ended, but relatively steep lapse rates from the surface to 2km and remnant BL moisture has kept flurries going this afternoon. Flurries will gradually end from the west through 22Z as the BL continues to dry and inversion tops lower with increasing subsidence.

Tonight and Wednesday...

The evening will be quiet with increasing mid-high clouds ahead of the approaching weak clipper system. Light snow is expected to move in after midnight, with PoPs being bumped up slightly. Some of the negatives with this system are; fast speed, the fact that the strongest forcing remains below the favorable dendritic growth zone, and a large area of drier air below 700 mb which will need to be saturated before snow develops at the surface. Fairly weak, but there is noteworthy FGEN in the 850-700 mb layer which should help in saturating the low levels within an a few hour period.

Given the speed of the system, a short lived 4-6 hr light snow event is anticipated with minor accums. Both the 00Z and 12Z HREF 12 hr snow amounts ranged from only a few tenths of an inch to a max member between 1-1.5 inches across central Indiana. Have opted to take the middle ground with most areas seeing around 0.5 or less with up to 1 inch in NW portions where slightly longer snowfall time should boost totals. Despite the minor accumulations, the only issue worth noting is the timing of the snowfall with the morning rush hour. Will issue an SPS to account for this impact to the traveling public.

The snow may mix with or change over to light rain before ending in the southeast part of the forecast area late tomorrow morning. SW winds will increase during the afternoon with highs warming into the 40s and 50s by afternoon.

LONG TERM (Wednesday night through Tuesday)

Issued at 321 PM EDT Tue Mar 17 2026

Wednesday Night into Thursday...

Another weak mid level shortwave will move SE across the western Great Lakes and upper MS valley ahead of the building upper ridge over the Rockies/High Plains. Associated WAA and increasing SW flow may support some elevated showers as mid level WAA kicks in and aids in saturation. Some of the forecast soundings suggest there is ever so slight amount of MUCAPE (100-200 j/kg) centered around 700-600 mb layer that an isolated TS can not be ruled out, but chances are low enough that have left it out of forecast.

Thursday Night through Saturday...

Shower activity should move quickly out of central Indiana by Thursday afternoon. As heights continue to build and SW flow strengthens in the boundary layer, expecting temps to be closer to 75 percent NBM guidance with highs 70-75 Friday and 75-80 Saturday, as opposed to the current NBM forecast highs 62-67 on Friday and 67-72 on Saturday. Moisture will continue to flow northward and will keep min RH values relatively high to preclude any significant fire weather concerns.

Sunday and beyond...

Guidance becomes a little more uncertain going into early next week. General agreement exists in a pattern change with the upper ridge over the plains flattening as stronger shortwave energy rides all the CONUS/Canadian border. Depending on the timing of an associated cold front, (faster with the Operational Euro) current forecast NBM temps for Sunday near 70 could be in jeopardy. In addition, little to no Pops from the NBM during the Sunday to Monday period is concerning considering the ample moisture (PWAT 150% of normal) ahead of the front. Albeit it there will be a fairly stout EML originating from the Desert SW/Plains. By Tuesday seasonably cool temps and mainly dry conditions are expected with high pressure building south out of the Great Lakes region.

AVIATION (18Z TAF Issuance)

Issued at 135 PM EDT Tue Mar 17 2026

Impacts:

- P6SM -SN, wind gusts, and MVFR ceilings ending by late afternoon. - Period of -SN late tonight with MVFR ceilings/vis and brief IFR vis after 06Z-09Z ending between 12-15Z. - VFR conditions tomorrow afternoon with increasing winds.

Discussion:

Light flurries with P6SM vsbys will end by late afternoon with VFR conditions developing. A weak storm system will move across the terminals later tonight (after 06Z) with MVFR ceilings and MVFR visibilities developing from west to east through 09Z. Brief IFR visibilities are possible mainly after KIND/KLAF. Snow and MVFR conditions are expected to improve between 12 and 15Z from west to east. Wind gusts this afternoon will diminish with sunset, with winds overnight being 5-10 kts shifting from West to South. Wind gusts may again approach 20 kts tomorrow afternoon.

IND WATCHES/WARNINGS/ADVISORIES

None.