textproduct: Detroit/Pontiac

KEY MESSAGES

- A little warmer and more humid today and Monday.

- Isolated strong to severe thunderstorms today, with a more organized severe weather threat arriving late Monday. Damaging winds are the primary hazard both days.

DISCUSSION

Prevailing northwest flow in the mid-upper levels will persist across the Great lakes region for the next couple days given the position of the large mid level ridge extending across the Rockies and high plains.

An ongoing gradual influx of high low level theta e air will contribute to a warmer and more humid day today. This in turn will translate to building instability during the course of the day, with various hi res solutions forecasting 0-1km MLCAPE values ranging from 1k to 2k J/kg. The northwest flow will also contribute to a strongly sheared environment, with 0-6km bulk shear values forecast to range from 30 to 50 knots across Se Mi. Model soundings indicate a mid level warm layer resulting in a respectable degree of capping, which will likely limit convective coverage today. Subtle large scale forcing via low a amplitude mid level short wave will offer a potential for some erosion of the cap today, warranting low chance pops. Taking into consideration the deep layer shear and good downdraft CAPE, any thunderstorm that initiates will be capable of producing damaging wind gusts.

Recent CAMs solutions continue to indicate the potential for several clusters of thunderstorms across the Great Lakes region tonight through Monday night. Trends within the model solution space are suggesting the higher convective probabilities tonight into the first half of the day Monday residing either over western Lower Mi or Wisconsin/Illinois along an axis of high instability. Within the model probability space, convective potential across Se Mi increases late Monday afternoon into Monday night. A stronger mid level short wave and associated sfc front will provide the dynamic forcing to trigger more widespread convection. A continued strongly sheared environment will remain supportive of severe convection, the coverage and intensity of which will rely on available instability. The uncertainty in early day convective trends will play heavily into late day available instability. The potential afternoon recovery in temps with sfc dewpoints in the upper 60s/near 70 suggest diurnal recovery may be swift. For this reason, SPC continues to have all of Se Mi in a slight risk Monday. The uncertainty in the evolution of early day thunderstorm clusters has prevented an outlook upgrade at this time.

Amplification of the longer wavelength trough across the mid Atlantic/northeast toward mid week will drive slight cooler and drier air across Lower Mi. Increasing anticyclonic flow will also warrant an overall dry forecast mid week.

MARINE

Light southwest winds draw warmer air and greater instability into the central Great Lakes leading to increasing thunderstorm activity today, including the chance for strong to severe storms this evening and tonight. The primary low pressure system then tracks across the northern Great Lakes during Monday. Thunderstorm activity continues to increase coverage and intensity with this system, especially along the trailing cold front that brings a chance of strong to severe thunderstorms as it moves through the region. Outside of storms, wind and waves are low until the northerly wind shift post front late Monday night into Tuesday when speeds likely reach 25 to 30 knots over southern Lake Huron. If the low deepens enough over the Eastern Great Lakes Tuesday evening, a short period of gales could even come into play. Winds slowly diminish on Wednesday as large area of high pressure over the Western Great Lakes slowly advances east, arriving on Thursday. This will assure dry conditions for those days.

HYDROLOGY

Convective rainfall chances will increase Monday afternoon and will peak Monday evening. Locally intense rainfall rates will be possible with any convection. There is the potential for a couple rounds of showers/thunderstorms over some areas during this time period. Probabilities for a quarter to one inch of rain are moderate to high. The chances for locations to exceed an inch are low (less than 20 percent) at this time.

PREV DISCUSSION

Issued at 1153 PM EDT Sat Jul 25 2026

AVIATION...

VFR ceiling of 4-6 kft over most of Lower Mi is the result of moisture slowly increasing within the diffuse pattern between Atlantic coast high pressure and low pressure slowly organizing from the central Plains into central Canada. The clouds are ahead of the surface warm front wavering north-south along the MS river valley. This front is not projected to move much toward Lower Mi late tonight leaving the expectation for low VFR ceiling to persist with a few patches of MVFR reaching the SE Mi terminal corridor from the primary area that extends from the upper Midwest into the lower Ohio valley.

Shower and thunderstorm trends are also being monitored as the weather focus for late tonight and Sunday. Predictability remains low, however recent hi-res model data suggests isolated showers develop within the nocturnal cloud field late tonight to early morning, mainly toward northern and western Lower Mi. That is followed by scattered thunderstorm potential just about anywhere in SE Mi within an uncapped profile and as daytime heating builds from late morning through the afternoon. A Prob30 is introduced in this forecast issuance for the usual mid/late afternoon hours of peak instability with further coverage and timing refinement likely in later updates.

D21/DTW Convection... There is a low chance of thunderstorms Sunday afternoon and evening. Confidence in coverage and timing remain low.

DTW THRESHOLD PROBABILITIES...

* Moderate for ceiling 5000 ft or less late tonight through Sunday.

* Low for thunder Sunday afternoon and evening.

DTX WATCHES/WARNINGS/ADVISORIES

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