Area Forecast Discussion

KEY MESSAGES

- Periods of rain return tonight though Sunday morning with locally heavier rainfall possible at times, and a few thunderstorms.

- Fog settles in overnight, becoming locally dense at times.

- Lingering showers exit by midday Sunday, followed by a cool and cloudy pattern into the middle of the week.

- Areas of showers are possible again late Tuesday into Wednesday.

DISCUSSION

Modest mid/upper level westerlies reside over the northern Great Lakes and Ontario this afternoon while lower column flow orients more southwesterly. This has led to steady moisture advection and broad morning shower activity, most of which has briefly tapered off. The main concern for this evening and overnight will be the positioning of an elevated warm front which will anchor additional shower activity, including the potential for a few thunderstorms. Latest NWP tendencies indicate a southward shift in this axis, favoring areas south of I-96/696 by late evening. CAPE metrics are meager at best with lapse rates AOB 6.0 C/km. No severe weather expected with any embedded thunderstorm structures. However, boundary-layer condensation pressure deficits indicate a high likelihood for areas of overnight fog. Potential exists for locally dense patches at times, therefore, a Dense Fog Advisory may be needed on short notice.

The large-scale pattern remains intact to start the day Sunday as the geopotential height field stays perturbed. Expect additional rounds of showers and perhaps a couple rumbles of thunder as the warm sector aloft begins to retreat. Split flow moves in from west to east overhead after 18Z, leading to subsidence/drying. Meanwhile, 1028 mb surface high pressure builds from Manitoba into central Ontario, backing gradient flow northeasterly. This helps promote further drying from north to south, dissolving lingering midday shower activity confined to areas south of I-94. Some clouds may linger into Sunday night, but temperatures should still hold around 5-10 degrees below climatological averages.

Unsettled conditions persist over the Ohio Valley early next week, although the expectation is that the ridge should remain strong enough and in proximity to Southeast Michigan to prevent much spillover of showers into the Lower Peninsula. Thermal troughing expands further across the Midwest, marked by 850 mb temperatures in the mid single digits (Celsius), which suggests daily highs closer to 10F below normal through Wednesday if not longer. A shortwave feature aloft could close off somewhere over the northern Ohio Valley late Tuesday into Wednesday. This would present the next opportunity for additional rainfall, in slightly more widespread fashion.

MARINE

Stalled frontal boundary maintains shower chances over the southern Great Lakes through Sunday. Expansion of strong high pressure over northern Ontario finally shunts this front deeper into the Ohio Valley. Locally, the central Great Lakes reside on the edge of this high resulting in a respectable gradient across the region throughout the entirety of the early week period. This supports moderate northeasterly through Tuesday before shifting more easterly by Wednesday (while maintaining strength). While gales currently look unlikely, onshore flow warrants long duration Small Craft Advisories for all nearshore waters.

HYDROLOGY

Additional showers are expected overnight, some of which will be capable of producing heavy rainfall, more so for areas south of M-59 where potential exists for training/repeated showers. Morning rainfall was less productive than prior expectations, therefore tonight's flood threat is slightly lower. However, tonight's shower activity could lead to localized new rainfall totals in excess of 1 inch. Current data suggests the I-94 corridor to the Ohio border will experience the highest chances for the highest rainfall rates. Ponding in low-lying areas and urban flooding are the primary threats, with minor rises on area rivers and streams likely. Additional lighter showers may continue through Sunday morning, before precipitation tapers off Sunday afternoon.

PREV DISCUSSION

Issued at 1239 PM EDT Sat Sep 19 2026

AVIATION...

Quasi-stationary elevated frontal zone will remain draped across the southern Great Lakes region through the forecast period. Plenty of low-level moisture to generate areas of IFR ceilings within the current batch of light rain move across the central and southern portions of the Southeast Michigan airspace. Rain will taper off later this afternoon - however, ceilings will remain MVFR to occasional IFR into tonight. Another batch of rain with embedded convection will expect to squeeze east out of Southern Wisconsin and northern Illinois tonight - with the best coverage across the Detroit terminal airspace. Winds will remain easterly through Sunday.

D21/DTW Convection...Low potential exists for an isolated embedded thunderstorm within periods of showers tonight.

DTW THRESHOLD PROBABILITIES...

* High for ceilings aob 5000-ft this afternoon through tonight.

* Low in thunderstorms through tonight.

DTX WATCHES / WARNINGS / ADVISORIES

MI...None. Lake Huron...Small Craft Advisory from noon Sunday to 10 PM EDT Wednesday for LHZ421-422-441>443.

Lake St Clair...Small Craft Advisory from 8 PM Sunday to 10 PM EDT Wednesday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 8 PM Sunday to 10 PM EDT Wednesday for LEZ444.