textproduct: Detroit/Pontiac

KEY MESSAGES

- Additional shower and thunderstorm chances today and Friday. Heavy rainfall is possible.

DTW THRESHOLD PROBABILITIES

* Low for ceiling 5000 ft or less early this morning and this afternoon.

* Moderate for thunderstorms this afternoon into the evening.

PREV DISCUSSION

Issued at 253 PM EDT Wed Sep 2 2026

DISCUSSION...

Hot and humid conditions continue through the evening, boosted by low 70s dewpoints and highs in the low 90s. This has brought peak heat indices across the Detroit Metro region into the low 100s which will linger through early evening, which has also established a robust pool of instability across all of SE Michigan. Question remains how strong the cap is, which has limited convection from fully blossoming in an otherwise favorable thermodynamic environment. Observational cues show this cap eroding across the Saginaw Valley region and other boundaries outside of the CWA, while inbound moisture suggests further erosion this evening.

SWODY1 Slight Risk thus persists given the conditionally favorable severe environment. Bulk parameters are impressive, as SPC mesoanalysis reports SBCAPE up to 4000 J/kg and 0-6km bulk shear over 40 knots due to a mid-level jet impulse aloft (h5 winds of 50- 55 knots). This should be supportive of organized multicellular and/or supercellular structures as shear vectors are oriented ~45 degrees to the initiating boundaries. Low confidence however exists in the initial development of storms and subsequent coverage/evolution as there will be multiple weak forcing mechanisms in play. Thus, a wide spectrum of outcomes expected across SE Michigan, with the most bullish scenarios producing damaging winds to 70 mph and hail over 1.5". These solutions carry higher confidence for the Saginaw Valley/Thumb than the metro Detroit region. While low level curvature is not prevalent attm, lake breezes/ storm outflow could locally augment hodographs to support an isolated tornado threat as well. Progressive storm motion generally limits long duration rainfall concerns this evening, although heavy downpours are likely.

Episodes of showers and thunderstorms then continue overnight through the end of the work week, with low predictability in timing and coverage. The unsettled pattern will be supported by a baroclinic axis that lingers over SE Michigan over the next several days, keeping plenty of instability around within a seasonably hot/humid airmass. Highs Thursday again approach 90 degrees with heat indices pushing well into the 90s to near 100 degree readings in urban areas, depending on cloud cover/convective coverage. Much of our shower/thunderstorm chances will be determined by upstream MCS development and the propagation of these systems into SE Michigan as ridging builds over central CONUS. Most likely cadence for these storms (based on pattern recognition) is a wave of nocturnal/early morning convection followed by reinvigoration of storms later in the day with the peak heating cycle that repeats until the front fully clears south of the state line this weekend.

The building ridge causes mid-level winds to veer from west to northwest by end of week, drawing in cooler air that alters both low and mid-level thermal profiles. Ultimately this causes the severe threat to decrease Friday-the weekend, despite shower and storm chances remaining in the forecast. A cooler pattern is expected this weekend, with highs falling into the upper 70s.

MARINE...

Winds and waves remain below threshold criteria across the central Great Lakes, aside from a few thunderstorms passing through a very muggy air mass this afternoon and evening. Gradient winds will shift from southwest to northwest once a weak cold front drops southeastward through region. Convective chances decrease a bit overnight within the wake of the slowing front, and winds could briefly trend towards calm. A low confidence forecast persist through the end of the week and early this weekend as a ridge over central CONUS remains quasi-stationary. This offers several additional opportunities for periods of showers and thunderstorms. MWS and SMW headlines will continued to be used to address short- term local watercraft concerns. No long-fused headline concerns through the weekend, although areas of dense fog could become an issue again late tonight into Thursday morning for portions of the waterways.

HYDROLOGY...

First round of showers and thunderstorms is ongoing across the Saginaw Valley and Thumb regions, with chances continuing overnight. The hot and humid airmass will support heavy downpours within most thunderstorms, although progressive nature of storms limits duration. Any strong thunderstorm will have the potential to produce a quick 1-2 inches of rain, which can lead to localized minor flooding of roads and poor-drainage areas. There are currently no indications of training storms, though more extensive flooding would become a concern if a mature MCS develops or storms repeatedly impact the same area.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None.