textproduct: Detroit/Pontiac

KEY MESSAGES

- Redevelopment of rain showers and some isolated thunderstorms will be possible tonight and overnight, along or south of M59.

- There is a low chance for strong to severe thunderstorm development with this activity.

- Rain and thunderstorm chances continue into the midweek period.

DISCUSSION

Expansion of high pressure across the upper Midwest will progress a cold front into southern Michigan where the boundary is then expected to slow and stall out tonight. This will retain an area of enhanced theta-e across southern Michigan overnight, characterized by PW values nearing 2" closer to the MI/OH border along with 850mb dew points ranging between 12-14C. Low level convergence and weak shortwave impulses within this region of higher moisture will be the focal point for renewed showers and possibly thunderstorms this evening through at least tomorrow morning.

For tonight, expansion of renewed showers and isolated thunderstorms will be more favorable around and south of M59. Any arrival of convection between 23Z - 02Z may be able to capitalize on a brief increase in surface instability along the nose of enhanced theta-e ahead of the cold front. This coupled with moderate low to mid level lapse rates and 0-6km bulk shear around 35 knots will bring some low end chances for an isolated strong to severe thunderstorm. Any stronger development will be capable of producing localized stronger wind gusts from a wet microburst. SR-hodographs also show a modest streamwise component from 0-3 km, highlighting potential for some better organization, but all said, poor buoyancy with unfavorable timing of convective potential will be a major hindrance to any robust convection. SWODY1 highlights a marginal risk for several weather for this activity.

Severe chances are then mitigated overnight once surface instability wanes and conditions turn more elevated. Zonal low to mid-level flow will bring continuation of shower and storm potential overnight through tomorrow afternoon. Any repeated shower and thunderstorm will have the low potential to bring localized flooding in flood prone locations. See the hydrology section for additional details.

The frontal boundary will waver across southern Michigan late Wednesday into Thursday, providing additional chances for showers and thunderstorms through the midweek period. Some respite from rain chances will be likely late Thursday into Friday as the southern periphery of high pressure builds in across the Great Lakes, but additional chances for showers and storms, possibly heavy rain, will re-enter on Saturday as storm complex derives from the Plains progresses into a stronger baroclinic zone. There is uncertainty this far out regarding where any enhanced forcing will align, with mid-range models highlighting anywhere from central Michigan to locations south into the Ohio Valley as potential zones for elevated QPF.

MARINE

An occluded low pressure system tracks into Hudson Bay this evening with its southwesterly low-level jet easing out of the northern Great Lakes with time. The core of the strongest winds has already exited the area and the Gale Warning will be allowed to expire on time at 4 PM. The system pushes a cold front across the area overnight, causing southwesterly wind to quickly veer to north and northeast by Wednesday morning. Ahead of the front this evening and overnight, additional scattered showers and a few thunderstorms will be possible mainly for Lake St. Clair and western Lake Erie. An isolated storm may be strong to severe with wind in excess of 34 kt the main threat. High pressure passes to the north of the lakes on Wednesday, sustaining continued northeasterly flow of 10 to 15 kt. A chance of showers and storms lingers around the southern Great Lakes through Wednesday and Thursday as the cold front stalls in the vicinity.

HYDROLOGY

Redevelopment and expansion of rain showers with some embedded thunderstorms will be possible tonight and overnight, most favorable along or south of M59. Any thunderstorm development will be capable of producing brief but heavy downpours. New rainfall totals from this afternoon through tomorrow morning are expected to range between a quarter-inch to a half-inch, however, any thunderstorm development will likely produce highly localized totals that reach or exceed one inch. This will bring a low chance for localized road flooding or minor flooding of low-lying and urban area through tomorrow.

PREV DISCUSSION

Issued at 1242 PM EDT Tue Sep 15 2026

AVIATION...

Regional radar suggest areas of showers and isolated thunderstorms likely to continue during the early to mid afternoon hours as mid level short wave energy track along an elevated frontal boundary and moisture axis. Observational data indicate the greatest coverage of showers will remain at PTK northward during the afternoon. The advection of instability into metro Detroit during the late afternoon and evening will increase the chances for thunderstorms tonight, with the probabilities highest in the 03Z to 06Z time frame. The development of low level inversion tonight and ample low level moisture in place will increase the chances for MVFR conditions in both ceilings and visibility restrictions late tonight through Wednesday morning.

D21/DTW Convection...Increasing elevated instability is supporting additional convection across SW Lower Mi early this afternoon, which may impact portions of the metro airspace this afternoon. Additional convective development is forecast later this evening along the lead edge of an axis of instability lifting into the area from the southwest.

DTW THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less this afternoon and evening. High tonight and Wednesday.

* Moderate in thunderstorms today and tonight.

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.