Decatur, IN 46733 Weather

Key Messages

- Dense fog is expected this morning, particularly along and east of Interstate 69. More patchy fog is possible tonight with the greatest chances across northeast Indiana and northwest Ohio. Some locally dense fog is possible again early Thursday morning.

- Dry weather will continue through the weekend with temperatures slightly above normal. Temperatures are expected to cool to slightly below normal by next Tuesday and Wednesday.

Discussion

Issued at 320 AM EDT Wed Oct 21 2026

Satellite imagery early this morning depicts an expansive area of stratus/fog across northwest Ohio, with widespread dense fog developing across south central Lower Michigan and northwest Ohio. Weak easterly flow associated with eastern portions of low level anticyclone will support westward migration of this stratus/fog into far northeast Indiana over the next several hours. A Dense Fog Advisory has issued earlier this morning for Hillsdale Co MI and all of NW Ohio counties, and based on current trends, a westward expansion will likely be required. With expansive low level anticyclone in place and very weak low level flow, diurnal mixing will likely be slow to erode stratus/fog, with areas of fog persisting through the 14 to 15Z timeframe.

Otherwise for today will be monitoring the progress of a progressive mid/upper level short wave trough across the Upper Midwest this morning as it reaches the western Great Lakes region. A narrow axis of mid level moisture/patchy mid level clouds will likely remain north of the local area while another area of mid clouds associated with mid level short wave progressing through mean upper ridging will largely remain displaced to the west from the Central Plains to the Mid MS Valley. A persistence forecast largely utilized for high temperature forecast today as little thermal advections have been noted over past 24 hours with similar poor mixing profiles today and similar good amounts of insolation.

Passage of the Great Lakes short wave this evening will allow for reinforcement and southwestward shift to low level anticyclone across the region. This should yield a weak northeasterly low level flow profile for tonight which once again raises the question of some enhancement to fog development downwind of eastern Great Lakes. Given northeast trajectories, greatest confidence in fog development tonight is far NE IN/NW OH mainly along and south of US Route 24, but some patchy fog will be possible once again for many areas east of I-69. THe fog may become locally dense once again early Thursday morning.

A stable wave pattern will maintain through the first part of the weekend with an eventual shift of longwave upper ridge axis east of the local area by 2nd half of the weekend. This should allow for Sunday to realize the warmest temperatures of the period in the low to mid 70s. Longwave predictability begins to break down early next week with large discrepancies in how phasing is depicted with western CONUS closed upper height perturbations among various deterministic/ensemble guidance. Some indications that stronger frontal forcing will develop northwest of the local area late weekend/early next week as southwest CONUS upper wave pushes east and dampens, but given uncertainty in progression and depth of this wave as it reaches central CONUS argues for maintenance of mainly dry forecast at this time with expectation that frontal forcing will wane through time. Blended guidance idea of trend back to cooler conditions early to mid next week still appears reasonable.

Aviation

Issued at 150 AM EDT Wed Oct 21 2026

The primary aviation weather forecast issue will be on the potential of dense fog at KFWA this morning. Satellite imagery and sfc observations early this morning are depicting an expanding area of low clouds and dense fog across northwest Ohio, with a slow westward translation over past hour. Weak northeast flow associated with eastern periphery of low level anticyclone will continue to support westward expansion of these low clouds/dense fog from the eastern Great Lakes this morning, possibly affecting KFWA as early as 10Z. The time period of greatest potential of dense fog at KFWA appears to be in the 11Z-14Z timeframe. Will maintain VFR conditions at KSBN with expectation bulk of dense fog will be roughly along and east of the I-69 corridor. A short wave tracking across the Great Lakes region will allow for low level anticyclone to refocus westward later today with weak low level northeast flow off the eastern Great Lakes again tonight. This could set up another night of patchy fog late Wednesday night at KFWA, although with the NE trajectories, best chances may be south of KFWA>

Iwx Watches

IN...None. 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.