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Mill Grove, Indiana Weather Forecast Discussion

168
FXUS63 KIWX 192328
AFDIWX

Area Forecast Discussion National Weather Service Northern Indiana 728 PM EDT Fri Sep 19 2025

.KEY MESSAGES...

- Another warm day on Saturday with highs into the 80s.

- Low chances (20-40%) for showers and isolated storms enter the forecast into mainly western IN and southwest MI on Saturday.

- Daily chances (40-60%) for showers/storms Sunday through Tuesday.

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.DISCUSSION... Issued at 214 PM EDT Fri Sep 19 2025

A persistent blocking pattern that has provided the area with upper ridging and associated warm/dry wx gradually breaks down into this weekend as broad troughing over the northern Plains finally releases east into the MS River Valley and western Great Lakes. The upstream leading warm front and moisture axis makes slow inroads into western IN and sw MI later tonight into Saturday morning, nearing the I-69 corridor by Saturday afternoon-evening. The largely elevated nature to the moisture advection and northwest bypass of more pronounced vorticity advection warrants holding on to lower end PoPs (20-40%) for scattered showers along this weak warm front. Guidance does hint at some weak diurnal instability developing on Saturday for a non-zero iso thunder risk west of I-69, although our recent dry spell hints at a greater mixout of mid-late day sfc dewpoints than modeled. Another warm day otherwise on Saturday with at least a partly to mostly cloudy sky.

Chances for much needed rain/iso storm chances do increase Sunday through Monday night. Deeper moisture advecting in, and numerous vorticity maxima tracking through in broad cyclonic flow, will provide these periodic shower/storm chances. There will be dry stretches in between these smaller scale (convectively augmented) mid level impulses, with ensemble guidance pointing to Sunday and Monday aftn-night for higher measurable rain chances (50-60%). Slight cooler highs, yet increasingly humid, the story otherwise during these periods.

Forecast confidence quickly diminishes Tuesday through Friday as renewed riding over southern Canada eventually cuts off an expansive low/trough somewhere across the Mid MS and OH Valleys. Models always struggle with these cut off, meandering, lows at this range. Opted not to veer from daily NBM rain chances (20-50%) as a result with the trough and frontal zone in the vicinity. Temperatures hover pretty close to seasonal norms otherwise for the mid-late week periods.

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.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 728 PM EDT Fri Sep 19 2025

On east and southeast trajectories, initially the mind goes back to a couple days ago where we advected the marine westward to get more moisture to trap underneath the inversion, which created a few hours of morning fog. This time, however, winds are forecast to be stronger as a low level jet edges eastward into the area from the slowly arriving trough to our west. So, with winds forecast to maintain speeds above 5 kts, will leave a mention of fog out of the TAFs. Wind speeds will need to be watched, however, because if the inversion takes hold sooner, we could be in for another batch of fog at least at FWA as the SREF 1 mi probabilities show for tomorrow morning. NAM Bufkit soundings show at least the formation of shallow fog at both sites, but cross over temps are not conducive at either site unless radiational cooling can take effect with weaker winds.

All that aside, will be going with prevailing VFR conditions because, while a shower or storm is possible mainly at SBN tomorrow afternoon, the possibility of reduced flight conditions is not high enough for its inclusion. Will be using a second group to handle the slow veering of winds toward southerly by the late afternoon.

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.IWX WATCHES/WARNINGS/ADVISORIES... IN...Air Quality Alert until midnight EDT /11 PM CDT/ tonight for INZ005>009-012>015-017-018-022>027-032>034-103-104-116- 203-204-216. OH...None. MI...None. MARINE...None.

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DISCUSSION...Steinwedel AVIATION...Roller

NWS IWX Office Area Forecast Discussion

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