495 FXUS63 KIWX 230426 AFDIWXArea Forecast Discussion National Weather Service Northern Indiana 1226 AM EDT Tue Sep 23 2025
.KEY MESSAGES...
- A dense fog advisory is in effect for Northwest Ohio and portions of Indiana and Lower Michigan. Visibility will drop to one quarter to one half mile in dense fog.
- An active weather period will continue through Friday with numerous showers and isolated thunderstorms.
- High temperatures will be in the 70s for the remainder of the week.
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.UPDATE... Issued at 1225 AM EDT Tue Sep 23 2025
Issued a dense fog advisory just before midnight for northwest Ohio counties; Hillsdale County, MI; and Indiana counties generally along/east of I 69 in the north; then along/south of US 24 elsewhere. Winds are calm with a decent inversion developing, trapping moisture from yesterdays rain close to the surface. Visibilities below 1SM have already been intermittently observed near Marion, IN and in much of NW Ohio--especially near Defiance, Ottawa, and Fulton, OH. Otherwise, reports of 1.5 to 3SM have been more common. As the inversion deepens overnight expect the patchy nature to become more widespread. Left out NW IN/SW Lower MI out for now given less low level moisture (rain was mostly to the E-SE today), slightly stronger flow (around 5 knots), and the potential for rain showers towards morning with the convective complex currently over Lake Michigan. Most guidance has this feature dying out right on our doorstep or north, but it is unclear as to whether or not any outflow boundaries move in and kick off some additional rain showers or increase the winds briefly. Most of the guidance keeps KSBN out of the foggy conditions, with visibility only potentially dropping to 5-6SM towards 12z. Conversely, KFWA guidance shows visibilities of 1/4 to 1/2SM possibly until 9 am or so. Have our dense fog advisory ending at 14z Tuesday for now, but may need to expand the time for a few counties if conditions actually linger into the 15-16z time frame. Will re-evaluate at the 4-5 am forecast update.
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.DISCUSSION... Issued at 214 PM EDT Mon Sep 22 2025
A positively tilted trof will settle south across the Upper Great Lakes region. This system will bring numerous showers to the forecast area as well as an occasional chance for a thunderstorm at times. WPC rainfall amounts of generally 1.00" to 1.50" are forecast through Friday. Heavier rainfall amounts so far today (as of 1 AM EDT) have been generally 0.25" to 0.50" over northeast Indiana and northwest Ohio. A short break in the heavier rain is expected before another upper level trof brings more rain Tuesday. Moderate drought conditions (D1) covered most of northern Indiana and northwest Ohio. Ft Wayne observed rainfall amounts since August 1st has been less than 2 inches (1.90) which is the 2nd driest in 130 years. So far, the rain that has fallen has not been sufficient to improve drought conditions.
While isolated to scattered showers are possible at time through Tuesday morning, more organized rainfall should develop Tuesday afternoon with the next impulse that moves across the area. The new WPC forecast indicates around a half inch of additional rain through 8pm Wednesday evening is forecast. Limited impacts are expected with this precipitation. Very minor rises on some rivers have been noted with this past round of rain. This next round of rain into Wednesday night should do little to effect river conditions.
Otherwise, dry weather if forecast from Friday night into early next week. Temperatures are expected to be near normal.
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.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 726 PM EDT Mon Sep 22 2025
As this trough pulls away, the left over moisture gets trapped under a forming inversion. There is definitely some uncertainty around whether the TAF sites will be affected by fog or stratus or both, but these tafs will run with the idea that SBN is affected by fog given they had clouds scatter out before sunset. FWA has the potential to see both stratus and fog. There`s also uncertainty around how low flight conditions go at both sites. Aviation guidance seems to point toward brief low MVFR or IFR conditions at SBN given their ability to scatter out before sunset, but lowered flight conditions look to stay longer and go lower at FWA, perhaps into LIFR. LAV guidance from both sites indicates weak sub-5 kts sustained winds which would point to some possibility for fog than if it was 5 kts or above at their lowest, which would point to solely a stratus situation. Have pulled SBN out of fog at around 13z with these tafs, but RAP time sections keep the low level saturation into the afternoon so wouldn`t be surprised to see it last longer than that. Will pass this along to the next shift to hone in on. FWA looks ready to give up its buck in the mid to late morning as it heads back into VFR.
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.IWX WATCHES/WARNINGS/ADVISORIES... IN...Dense Fog Advisory until 10 AM EDT this morning for INZ007>009- 017-018-020-022>027-032>034. OH...Dense Fog Advisory until 10 AM EDT this morning for OHZ001-002- 004-005-015-016-024-025. MI...Dense Fog Advisory until 10 AM EDT this morning for MIZ081. MARINE...None.
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UPDATE...MCD DISCUSSION...Skipper AVIATION...Roller
NWS IWX Office Area Forecast Discussion