517 FXUS63 KIWX 190534 AFDIWXArea Forecast Discussion National Weather Service Northern Indiana 134 AM EDT Fri Sep 19 2025
.KEY MESSAGES...
- Remaining warm through the weekend with above normal high temperatures in the 80s.
- Chances of rain return for the weekend, especially later Sunday into Sunday night (50-60%).
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.DISCUSSION... Issued at 207 PM EDT Thu Sep 18 2025
More of the same into tonight and Friday as upper level ridging lingers between a low pressure center over the North-central US and an upper trough over southeast Canada. A backdoor cool front associated with the southeast Canada trough drops into northern zones tonight into Friday morning with the only potential impact being patchy fog early Friday in its wake thanks to some marine influence from Lake Huron/Erie.
Weak height falls overspread the region Friday night into this weekend as the Plains low/upper trough evolves east toward the MS River Valley and western Great Lakes. This will bring initial low (20-30%) chances for a few showers into mainly western IN and southwest MI Friday night into Saturday as a weak shortwave and elevated warm front lift through. Most of the area will remain dry however with more clouds around and temps still above normal for late Sept.
Late Sunday into Sunday night still appears to be the best opportunity (50-60%) for greater rain shower coverage and perhaps a few embedded storms as a more pronounced shortwave and surge of deeper moisture track east-northeast through the western/lower Great Lakes. Predictability then falls off into next week as the broad upstream trough eventually cuts off under building south-central Canada heights. Opted to hold with NBM daily broadbrush PoPs as a result (mainly 20-50%) through at least the mid-week periods given expectations for moist low levels with a front and this meandering upper low nearby. High temperatures will be a bit cooler in this regime (near normal), though humidity levels will be more elevated.
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.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 133 AM EDT Fri Sep 19 2025
A weak sfc trough will continue to sag south and should stall out across extreme northern Indiana. Sfc dew points have risen a few degrees into the lower 60s in the wake of this front with some eastern Great Lakes marine influence. Hires guidance does indicate some increased fog potential in the vicinity of, and just in wake of this sfc trough, but this potential should remain north and east of KSBN/KFWA. Some patchy shallow fog is possible, but this appears to be more favorable in outlying rural areas and will continue to omit from 06Z TAFs. Otherwise, mid/upper level ridge will maintain its location today, eventually starting to shift eastward by this evening. Some weak sfc based instability is possible at KSBN later this afternoon, but better instability and forcing should remain across Illinois. VFR conditions are expected to hold through this period.
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.IWX WATCHES/WARNINGS/ADVISORIES... IN...None. OH...None. MI...None. MARINE...None.
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DISCUSSION...Steinwedel AVIATION...Marsili
NWS IWX Office Area Forecast Discussion