textproduct: Detroit/Pontiac

KEY MESSAGES

- Rain chances linger mainly south of I-94 this evening as a cold front drops across SE Michigan.

- Seasonably cool conditions will persist into the middle of week.

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

DTW THRESHOLD PROBABILITIES

* Medium for ceilings at or below 5000 feet this evening becoming low overnight into Monday.

PREV DISCUSSION

Issued at 400 PM EDT Sun Sep 20 2026

DISCUSSION...

Showers continue to dissipate as expected from north to south as drier air filters into the low levels. This process is the result of split flow moving in aloft and 1028 mb surface high pressure building out of central Ontario. A wind shift/cold front is being driven south by the strengthening anticyclone, and will eventually steer gradient flow northeasterly. Despite the influx of a drier Canadian air mass, stratocumulus clouds are expected to linger overnight given the cold advection over Lake Huron. Cooler again tonight, with temperatures dipping into the 40s for some locations farther north.

Readings hold below seasonal averages through the first half of the week, with mainly dry conditions prevailing as the ridge influence takes command. The exception will be closer to the Ohio border where a shortwave moves from The Plains into the Ohio Valley, before closing off and stalling. Expect vicinity showers at times Monday through Tuesday, although the rest of Southeast Michigan ought to stay dry and breezy, particularly during the afternoon hours as the ridge/subsidence wins out. Thermal troughing maximizes across the Midwest by Wednesday with 850 mb temperatures dropping into the mid (perhaps low) single digits (Celsius). The NAM shows that the coldest air should filter across Lake Erie, setting up a north-to- south thermal gradient over southeast Lower, with portions of Metro Detroit possibly seeing highs capped AOB 60F.

The synoptic pattern should lock up midweek as the closed mid/upper low orients in Rex Block formation, immediately south of the Ontario anticyclonic wave. A southern stream wave will fold into the Ohio Valley and break the stationary waves late Wednesday into Thursday, offering some potential for showers, more so for the southern half of the forecast area. It will take some time before temperatures begin to recover, as easterly lower column flow hangs on toward the end of the workweek.

MARINE...

The central Great Lakes reside on the southern fringe of broad northern Ontario high pressure through the first half of this week. The combination with a lingering stalled frontal boundary over the Ohio Valley results in a respectable gradient across the region maintaining moderate northeasterly winds through Tuesday (gusting 20- 25kts with 30kts possible in the Saginaw Bay). Waves rippling along the frontal boundary could offer some sporadic shower chances over the southern Great Lakes though influence of high pressure is expected to keep most of the area dry. Westward drift of high pressure leads to a shift toward more easterly flow Wednesday though with little to no reduction in wind speeds. Gales remain unlikely though onshore flow warrants long duration Small Craft Advisories for all nearshore waters.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory until 10 PM EDT Wednesday for LHZ421-422- 441>443.

Lake St Clair...Small Craft Advisory until 10 PM EDT Wednesday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EDT Wednesday for LEZ444.