textproduct: Detroit/Pontiac

KEY MESSAGES

- Scattered showers and a chance of thunderstorms return to the area today. The best chance of storms and heavy rainfall is late afternoon and evening south of I-69.

- A chance of showers lingers Wednesday, again mainly south of I-69, until becoming more likely again Wednesday night and Thursday.

- Dry weather with temperatures around normal are projected for Friday.

- A first look at the weekend indicates showery weather but mild temperatures Saturday and Sunday.

DISCUSSION

A large and strong low pressure system is developing on schedule while entering NW Ontario early this morning. The system moves toward James Bay while drawing a band of showers with a few thunderstorms across Lower Mi this morning followed by additional activity along the the trailing cold front tonight. The cold front then becomes the forecast subject for continued shower/storm prospects through Wednesday and Thursday.

Early morning observations indicate the primary band of showers/storms aligned with strong low level jet forced moisture transport. The eastern fringe is tied more to elevated sections of the warm front still moving in from the mid MS valley. Shower clusters continue to develop NE with some enhancement due to increasing nocturnal/elevated instability. The northward displacement from the surface warm front also means there is still a substantial layer of dry air in the low levels for these showers to overcome through the morning. The 00Z DTX sounding shows this as it was last evening and which model soundings indicate will remain a limiting factor until the larger scale moisture axis moves in from the NW mid to late morning. This primary moisture axis, and the showers/storms within, continues to sink into central Lower Mi and toward the I-69 corridor by noon. As this occurs, there is still a considerable weakening trend depicted across the range of model solutions which passes the eye test considering changes in the larger scale setup. The advective process shifts into Canada and leaves the moisture axis overhead where it loses nocturnal/elevated instability while also moving farther away from support provided by the upper jet and parent mid level short wave.

Other than a rumble of thunder this morning, a greater chance for thunderstorms in SE Mi is held during the late afternoon and evening. Early to mid afternoon showers remain scattered within the moisture axis while a narrow surface based warm sector builds into Lower Mi ahead of the cold front. SW flow gusting near 30 mph carries in a resurgence of surface Td back up into the 60s to around 70 with southward extent. Afternoon highs in the lower to mid 80s toward the Ohio border help projections of HREF mean surface based instability reach 1000 J/kg after 21Z, but just barely up into Lenawee and Monroe counties although also with 30-40 kts of 0-6 km bulk shear. The range of hi-res models then depict a late peak heating cycle convective initiation mainly 21Z to 00Z along or just ahead of the cold front which lasts through the evening. This is a slower/later trend on initiation timing which is a limiting factor for development farther north from the Ohio border. The updated SPC Marginal Risk up toward the I-94 corridor looks good in that regard, and which highlights an isolated storm capable of some entry level wind organization, or a precip-loaded gust, until the line exits south and east after midnight.

A chance of showers lingers toward the Ohio border late tonight and Wednesday as the passing cold front stalls through central to southern IN/OH. The position of the surface front and active zones aloft are slightly farther south compared to recent model cycles which is reflected in the NBM carrying POPs mainly south of the I-69 corridor until later Wednesday night. This is when the next low amplitude mid level wave and surface low are projected to slide along the frontal zone, however the new 00Z model run maintains the increased spread in QPF solutions noted in yesterday's forecast. Consensus of GFS, NAM, Canadian is mostly south of the IN/OH border while the ECMWF is well north over southern Lower Mi. ECMWF ML/AI runs suggest the deterministic solution is too far north, but this uncertainty remains in the NBM with likely POPs brushed across all of SE Mi later Wednesday night and early Thursday.

Extended time range models build surface high pressure southward enough to give us a break of dry weather Friday, in the subsidence wake of the passing short wave. However, model trends are faster bringing moisture back into Lower Mi Friday night into Saturday leading to concerns that showers then remain active through Sunday.

MARINE

An occluded low pressure system advances across northern Ontario today, directing a strong southerly low-level jet across the Great Lakes. A Gale Warning remains in effect for Lake Huron north of Alabaster through 4 PM where gales of 35 to 40 kt are forecast. Farther south, gusts of 20 to 30 kt will be more common through this afternoon and Small Craft Advisories remain in effect for the Lake Huron nearshore waters. A band of showers with a few embedded thunderstorms works across the area this morning with the highest coverage across Lake Huron. Additional scattered showers and thunderstorms then become possible across Lake St. Clair and western Lake Erie during the late afternoon and evening ahead of a cold front. This front eases across the area tonight, bringing the end to showers and causing wind to shift from south/southwest to north/northeast by Wednesday morning. High pressure passes to the north of the lakes on Wednesday, sustaining continued northeasterly flow of 10 to 15 kt.

HYDROLOGY

Showers and a chance of thunderstorms increase across Lower Michigan as a moisture rich airmass surges back into the region today. The warm and humid air moves in ahead of a cold front which tracks through late in the afternoon and this evening. The front then stalls out across the northern Ohio Valley before lifting back north later this week. This will result in multiple opportunities for widespread rainfall throughout the week. In the near-term, the best opportunity for heavy rain will be south of I-69 this evening where thunderstorm development may enhance rainfall rates to over an inch per hour. Depending on where the front stalls, rain may linger overnight to produce storm totals over one inch by Wednesday morning with training storms not out of the question. This pattern presents a chance for localized road flooding, or minor flooding of low-lying and urban areas during the mid to late week period.

PREV DISCUSSION

Issued at 1156 PM EDT Mon Sep 14 2026

AVIATION...

Thickening high based cloud overnight, as elevated moisture transport increases along the southern flank of a strengthening low level jet positioned north of the region. This process brings potential for scattered shower activity late night and early Tuesday, particularly from PTK northward, with overall coverage and intensity likely limited too some degree by ample dry air held within the lowest layers. This will support predominant VFR conditions through this time. Prevailing wind from the southeast tonight, veering to southerly with some modest gustiness for the afternoon. Secondary window for convective development may emerge along the cold frontal boundary Tuesday evening with a focus across the Detroit corridor.

D21/DTW Convection...No thunderstorms are forecast through Tuesday afternoon. A lower probability exists for thunderstorm development Tuesday evening /21z-01z/.

DTW THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less Tuesday afternoon and evening.

* Low for thunderstorms Tuesday evening.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None.

Lake Huron...Gale Warning until 4 PM EDT this afternoon for LHZ361>363.

Small Craft Advisory until 4 PM EDT this afternoon for LHZ421-422- 441>443.

Lake St Clair...None.

Michigan waters of Lake Erie...None.