textproduct: Indianapolis

KEY MESSAGES

- Widespread frost and localized freezing temperatures tonight - A Freeze Warning is in effect for much of eastern and portions of central Indiana, Frost Advisory elsewhere - Dry and quiet weather through the next 7 days with temperatures rebounding well above normal by midweek

DISCUSSION (This evening through Saturday)

Issued at 124 PM EDT Sat Oct 17 2026

Tonight Through Sunday Night.

Surface high pressure centered across the Mid-Mississippi Valley this afternoon will drift east across Indiana tonight, establishing optimal conditions for boundary layer decoupling. Strong synoptic subsidence in the wake of the exiting upper trough will maintain clear skies. Light and variable to calm winds are anticipated across the entire forecast area after 02Z with temperatures rapidly dropping out of the mid 50s and into the low 40s by late this evening.

The primary forecast challenge continues to center on overnight minimum temperatures and associated frost/freeze headlines. The aforementioned efficient radiational cooling will allow for temperatures to drop into the low to mid 30s across all of central Indiana with uncertainty remaining as to where the best chances for sub-freezing temperatures will be. As of early this afternoon, dew points remain generally at or above 32 but expect at least some additional drops as northerly to northeasterly flow continues. NBM continues to run on the cooler side of most hi-res guidance with the Canadian and its associated ensemble pushing down the mean, but with such efficient radiational cooling expected the Canadian may be closer to reality than the HRRR/NAM. The WRF-ARW which similarly handles efficient radiational cooling shows temperatures near to below freezing for much of central Indiana. Thus, generally expect all areas to see a widespread frost with more rural areas to see temperatures at or below freezing. Urban areas will end up a degree or two above, but with the uncertainty as to where the freeze will occur, not planning on adjusting the headlines at this time.

By Sunday, the surface anticyclone center slips eastward into the upper Ohio Valley and central Appalachians. Low-level flow will back to the south-southwest at 5 to 10 mph by afternoon. Model soundings show a dry atmospheric column with precipitable water values under 0.35 inches, supporting abundant sunshine. Boundary layer mixing up to approximately 900mb where temperatures recover to 6C to 8C will allow afternoon maximum temperatures to rebound into the lower to mid 60s. For Sunday night, modest south-southwesterly return flow will keep the boundary layer slightly mixed, holding minimum temperatures in the upper 30s to lower 40s and precluding significant frost concerns outside of isolated sheltered depressions.

Monday Through Saturday.

The medium-range period will be characterized by a stagnant, highly amplified synoptic regime featuring ridging over the eastern third of the CONUS and a deep closed trough digging into the Western States. With surface high pressure anchored off the Mid-Atlantic coast, persistent low-level southwesterly flow will advect a much milder continental airmass northward. 850mb temperatures are forecast to warm from 9C on Monday to near 13C to 15C by Wednesday and Thursday. Under mostly sunny to partly cloudy skies, daytime highs will peak in the upper 60s to lower 70s on Monday, reaching the mid to upper 70s Tuesday through Thursday, which is roughly 10 to 15 degrees above seasonal normals. Overnight lows will concurrently moderate into the 40s Monday night and the lower to mid 50s for the remainder of the week.

Dry weather will dominate the regional sensible weather through at least Thursday night due to deep-layer subsidence, strong capping around 800mb, and the diversion of synoptic moisture plumes well northwest into the Upper Midwest. Toward the Friday and Saturday timeframe, deterministic solutions diverge regarding the ejection speed of the western trough into the northern Plains. There are some signs that there may be a decaying frontal boundary nearing the area by late Friday but confidence is low in any precipitation chances with the strong ridging in place ahead of time.

AVIATION (18Z TAF Issuance)

Issued at 124 PM EDT Sat Oct 17 2026

Impacts:

-None

Discussion:

VFR conditions through the TAF period with clear skies expected as high pressure moves overhead. Northeasterly winds of 5-10kt will gradually drop to calm after 00Z with winds then gradually becoming southerly again after 12Z Sunday.

IND WATCHES/WARNINGS/ADVISORIES

Frost Advisory from 2 AM to 9 AM EDT Sunday for INZ021-028-029- 035-043>045-047-051>055-060>064-067>072.

Freeze Warning from 2 AM to 9 AM EDT Sunday for INZ030-031- 036>042-046-048-049-056-057-065.