textproduct: Detroit/Pontiac

KEY MESSAGES

- Rain and thunderstorm chances continue into the midweek period.

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

DTW THRESHOLD PROBABILITIES

* High for ceiling 5000 ft or less late tonight and Wednesday.

* Moderate for thunderstorms before sunrise.

PREV DISCUSSION

Issued at 910 PM EDT Tue Sep 15 2026

UPDATE...

An arc of instability has built into SW Lower Michigan and is expanding into portions of SE Michigan as of 9 PM local time. This has led to blossoming convection along a line from roughly Jackson to South Bend to Kankakee with cells moving east-northeast. A couple of these cells have acquired stronger updrafts with latest radar scans showing echo tops over 40.0 kft arl, and will likely cross the CWA border within the hour and remain along/south of I-94 as they march east-northeast.

These cells have quickly grown upscale, materializing into a heavy rainfall threat if they can hold together upon crossing the instability gradient. Rainfall rates may exceed 1" per hour in any thunderstorm activity, but the overall eastward progress of the line is encouraging for limiting duration at any one location. Will monitor for localized flooding concerns, particularly in low-lying and urban areas as discussed in the Hydrology section from earlier today. The deeper convective cells also warrant monitoring for a severe threat, but are competing against waning daylight and the low level subsidence bubble that was sampled in the 16.00z KDTX sounding. Main concern continues to be isolated gusts that could approach severe limits, more likely toward the Ohio border where dewpoints are flirting with 70 degrees. Storms however are moving into an environment that is more supportive of elevated convection. No major changes to thinking from the afternoon package.

PREV DISCUSSION... Issued at 353 PM EDT Tue Sep 15 2026

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.

DTX WATCHES/WARNINGS/ADVISORIES

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