textproduct: Detroit/Pontiac

KEY MESSAGES

- Scattered showers and thunderstorms tonight and Sunday morning, becoming more widespread Saturday afternoon. There is a Marginal/Isolated risk of strong/severe thunderstorms Saturday afternoon.

- Breezy and cooler conditions arrive Sunday with a lingering chance for showers.

- Dry weather with slightly below normal temperatures start off the week on Monday.

DTW THRESHOLD PROBABILITIES

* Very low for thunderstorms tonight. Moderate after 18z Saturday.

* Low for ceilings at or below 5000 ft Saturday morning.

PREV DISCUSSION

Issued at 301 PM EDT Fri Aug 21 2026

DISCUSSION...

A couple meso scale vorticity centers apparent on the latest radar/satellite composite which have emerged from earlier convection across eastern Wisconsin will track across southern and central Lower Mi late this afternoon. This added PVA with the advection of a narrow moisture and instability axis into Se Mi will support a chance for convection late this afternoon and evening. Ongoing deep layer moisture and weak elevated instability advection in advance of the longer wavelength inbound trough will sustain chances for convection across the entire forecast area through the night. Cloud cover and boundary layer moisture advection will lead to a milder night in relation to last night with min temps largely in the 60s.

Amplification of the longer wavelength trough will persist through the weekend with the main mid level positive vorticity axis forecast to pass across Se Mi during peak daytime heating Saturday. The resident moist axis and diurnal heating will contribute to weak instability by early Saturday afternoon. This will support high chances for showers/thunderstorms, especially during the afternoon. Cloud cover and potential early day showers will limit daytime highs to the 70s. ML CAPE values are therefore forecast to remain at or below 1500 J/kg. This and 0-6km bulk shear values at or below 25 knots will mitigate the severe weather risk. There has been some trends toward a little steeper mid level lapse rates Saturday, which could lead to some higher downdraft CAPE potential warranting an isolated risk for some stronger/severe convection. Mean total forecast QPF values have increased slightly over the last few model cycle, now around 4 tenths of an inch. High end totals (95th percentile) of 1 to 1.25 inches are possible within any slow moving convection.

The 12Z model suite has trended toward the evolution of a deeper more closed upper low over the eastern Great Lakes Sunday into Monday resulting from better phasing with secondary mid level PV anomaly dropping down from northern Ontario Sat night. This will drive a respectable thermal trough (850mb temps down to the single digits) across Lower Mi Sunday which now looks to persist into Monday. This will ensure seasonally cool (almost fall-like) temperatures to finish the weekend and start the new week. Steep low level lapse rates and moisture flux off the Great Lakes will contribute to ample cloud cover Sunday. This secondary short wave/positive PV anomaly is now forecast to brush across Se Mi Sun afternoon. Despite an overall lack of deep layer moisture, this wave may allow a brief uptick in convective cloud depth, offering at least a chance for some afternoon showers. A progressive northern stream wave is forecast to bring the next chance for showers/thunderstorms mid week (Wed/Thurs time frame). Ensemble members still show a fair amount of spread among timing and precip chances with this system .

MARINE...

The departure of high pressure into the Continental northeast will allow winds across the Great Lakes to back to the southwest this afternoon with increasing rain and thunderstorm chances building in across northern Lake Huron ahead of the next cold front. The cold front will progress across the Great Lakes through tomorrow morning and afternoon, expanding rain and thunderstorm chances across the remainder of the forecasted area. Winds will continue to veer to the northwest in the wake of the passing front, and will increase in intensity and remain elevated through Sunday as cooler is ushered in. Wind gusts will likely range around 25 to 30 knots through the weekend. The switch in wind direction from the northwest will quickly build wave heights in and around the Thumb which will likely result in the issuance of Small Craft Advisories by Sunday morning. High pressure builds back in Monday and Tuesday which will bring about lighter winds.

DTX WATCHES/WARNINGS/ADVISORIES

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