textproduct: Indianapolis

KEY MESSAGES

- Widespread frost with localized sub-freezing temperatures tonight into Sunday morning. A Freeze Warning has been issued for northeastern counties, with a Frost Advisory everywhere else.

- Dry conditions expected through the 7 day forecast. Temperatures are expected to Sunday onward with warmer then normal temperatures next week.

DISCUSSION (Today through Friday)

Issued at 222 AM EDT Sat Oct 17 2026

Through Sunday Morning:

Most of the forecast period will be rather stagnant as the upper low associated with yesterday's trough passage will detach from the flow and become cutoff over the Eastern Coast. This in combination with a weak split flow upper jet will keep mid to upper level conditions fairly similar through the weekend and into next week. While the bulk of the forecast will remain similar, slight fluctuations in surface pressure over the next 5-7 days will still lead to slightly different temperatures and wind speed/direction over the forecast period.

CAA will be strong through the morning hours, dropping dew points into the low 30s across northern portions of the area. Even though skies are clearing, brisk surface winds of 7-10kt will keep the PBL fairly mixed limiting diurnal cooling and saturation enough to mitigate frost formation for most areas. Sheltered areas over far NE central Indiana may see some patchy frost, but this will not be abundant enough to warrant headlines. Western portions of the forecast areas may fail to fall below 40 this morning as downstream cloud cover from Lake Michigan increasing downwelling longwave.

Continued CAA over the next 24 hours will lead to height rises beneath 850mb and therefor building high pressure through most of today. The centroid of this surface high is expected to overlap with the core of the mid level polar airmass late today and tonight of which will result in our coldest temperatures of the season. Frost looks definite for most of central Indiana on Sunday morning, but there is still some uncertainty in below freezing temperatures. Ensembles are starting to become more aligned on timing of the surface high passage of which should result in below freezing temperatures over northern and northeaster central Indiana tomorrow morning. A Freeze Warning has been issued for these areas, with a Frost Advisory for the remaining counties.

Remainder of Sunday through Thursday:

The surface high will push off to the east on Sunday, allowing for weak S/SE flow to develop over the Ohio Valley. This along with mostly clear skies will lead to a slight rebound in temperatures with highs on Sunday expected to be in the low 60s. Clear skies and dry surface conditions will continue large diurnal swings, but there should be enough of an air mass change to keep temperatures above freezing Sunday night into Monday morning. Frost potential will remain high, but headlines will depend if any hard freezes occur tonight.

Upper level riding will continue to build throughout the beginning of next week leading to subsidence and dry conditions. Continued S/SW flow west of the surface high will maintain the steady warming trend early next week as well. 850mb temperatures are expected to increase above 10C by Tuesday. This along with dry adiabatic lapse rates in the PBL should lead to daily temperature above seasonal normals Monday through Wednesday. Expect large diurnal swings to continue with lows in the 40s.

AVIATION (06Z TAF Issuance)

Issued at 121 AM EDT Sat Oct 17 2026

Impacts:

- Rain showers possible through 09Z at KLAF with minimal VIS impacts

Discussion:

Northerly winds off of Lake Michigan will continue low chances for rain and ceilings around 4000ft at KLAF. This could reach KHUF, but confidence is too low to include at this time.

The low level airmass will slowly dry throughout the day, leading to mostly clear skies from 15Z onward. While gusts will not be abundant a few isolated gusts to 20MPH will be possible this afternoon out of the NNE. This has not been included in this issuance due to low confidence, but is something that may be added is later updates.

As high pressure increases this evening, winds will slowly calm, with a predominant direction out of the ENE at 2-4MPH overnight.

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.