textproduct: Detroit/Pontiac

KEY MESSAGES

- Warm and humid again today with heat indices in the 90s, the warmest of which will be found closer to the MI/OH border and into the Metro region.

- There is a Marginal to Slight Risk for severe weather today. Severe weather development will be possible at all times today, but most favorable timing will be this afternoon into late tonight.

- Shower and thunderstorm chances continue into tomorrow.

DTW THRESHOLD PROBABILITIES

* Low for ceiling 5000 ft or less early this morning and this afternoon. Moderate after 00Z tonight.

* Moderate for thunderstorms this afternoon into late tonight.

PREV DISCUSSION

Issued at 345 AM EDT Thu Sep 3 2026

DISCUSSION...

For this morning... SPC mesoanalysis continues to showcase MUCAPE values around 2000 J/kg along with 35-40 knots of effective bulk shear with sufficient mid-level lapse rates around 5.5-6C/km. These conditions have supported repeated rounds of thunderstorms, some strong to severe, primarily along and and between M59 to I94. Initiation has taken place along a quasi-stationary frontal zone which has been reinforced from prior convective outflow. Additional showers and storms remain possible through this morning as this boundary provides a mechanism for ascent within this subtropical airmass. Given the degree of elevated instability and bulk shear, isolated strong to severe thunderstorms cannot be ruled out through the morning.

Warm and humid conditions are again expected this afternoon dewpoints again holding in the upper 60s to low 70s. Current thinking is that temperatures will be slightly lower relative to yesterday which decreases probabilities to reach heat advisory thresholds. Additionally, given where the frontal boundary is, some potential exists for showers and thunderstorms through the late morning and into the afternoon which if materialized, could temper temperatures locally. Although several hi-res solutions continue to retain an early day period of clearing and stronger insolation. Regardless, temperatures will be capable of pushing back into the upper 80s to low 90s through the MI/OH border into the Metro region with heat indices in the mid to upper 90s.

For this afternoon and evening, SE MI will be susceptible to renewed thunderstorm activity. One possible scenario will stream from activity upstream across Wisconsin or the western Great Lakes as a strengthening LLJ pools moisture and enhances convergence along the stalled frontal zone. Mean flow and forecasted storm motion would carry this activity SE towards lower Michigan through the afternoon and evening, placing all of SE MI within the corridor for potential strong to severe thunderstorm development. Surface based instability will increase with southward extend. SBCAPE around 1500-2000 J/kg is possible near the MI/OH border and tapers towards 1000 J/kg north of I-69. Deep layer shear around 30-35 knots remains solid for organized convection with all storm modes possible.

Damaging wind gusts will remain the primary hazard when taking into account strong low-level lapse rates, high PW, and strong buoyancy. This will support efficient precipitation loading for wet microbursts and/or consolidation of outflows with cold pool dynamics that can support bowing segments. Isolate large hail also remains possible given improving mid-level lapse rates approaching 6.5C/km. A large portion of SE MI has been upgraded to a Slight Risk in the latest SWODY 1, aligned where the better daytime instability is projected to reside.

Additional rounds of showers and storms then becomes increasingly likely late tonight into Friday morning as an elevated warm front strengthens from SE WI into lower Michigan. This has been a pretty robust signal in the latest 00Z runs. The boost in low to mid-level theta a with convergence along this boundary will help support an area of showers and storms overnight. While surface base instability diminishes during this time, elevated instability and strong shear holds which will maintain potential for organized convection. Storm threat would transition to hail given the more elevated nature of this activity along with localized heavy rainfall and flooding, especially with any repeated convection along the boundary. Some uncertainty resides how far east this activity will extend, but the trends still take activity to or south of M59 overnight.

Friday will again offer additional chances for rain and thunderstorm before ridge amplification across the Plains aids in reinforcing high pressure over the Great Lakes, which will work to decrease rain and thunderstorm chances this weekend.

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...

There will be multiple chances for thunderstorm development through the entirety of the day today, with the afternoon and evening hours affording the best time frame for some better coverage. Given that SE MI remains in a subtropical air mass, precipitation rates will be very efficient with any thunderstorms. A quick 1-2" of rainfall will be possible with any stronger thunderstorms which would lead to localized flooding concerns. Overnight, there is a signal for showers or thunderstorm development to then set up around or south of M59, which will be capable of producing an additional 1-2+" of rainfall pending where this rainfall axis sets up.

DTX WATCHES/WARNINGS/ADVISORIES

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