textproduct: Detroit/Pontiac

KEY MESSAGES

- Multiple rounds of showers and a few thunderstorms are forecast into Sunday. This afternoon into late evening the main area of concern for thunderstorms and heavy rain are along/north of M-59 and up into the I-69 corridor.

- Heavy rainfall is likely somewhere over northern Indiana, southeast Lower Michigan or northwest Ohio overnight tonight and Sunday. There is still uncertainty in where this axis will develop. It could reach as far north as Ann Arbor to Port Huron and bring flooding concerns, especially over urban areas.

- Dry weather returns on Monday, but it may become unsettled again for parts of next week with chances of showers. Temperatures will be close to average for early August.

DISCUSSION

A west-east axis of showers and embedded thunderstorms has begun to develop this afternoon along an broad axis of surface convergence as deeper moisture lifts north. This area is currently along/near the M- 59 corridor and expected to slowly lift north towards the I-69 corridor through this evening. This mornings raob from DTX showed PWATs above the 90th percentile for this time of year and a narrow pocket of elevated instability between 1-6km. Latest RAP analysis also shows this area generally uncapped, thus this pocket of instability is likely now surface based. While instability is not all too impressive, the warm, moist environment remains favorable for higher rainfall rates with any thunderstorm activity. Rainfall this afternoon and into tonight will be highly variable and dependent on where slow moving thunderstorm activity tracks.

Afternoon surface and satellite analysis show both the surface and upper-level low across central Illinois. With the low already having occluded across the Midwest and the upper-level wave becoming cutoff, it will be very slow to move east over the next 24-36 hours. Another wave of energy is progged to dig south across the region tonight and through Sunday, helping move the system along to the east. With these two waves of energy approaching the area through Sunday, there remain uncertainties in how the potential for heavy rain and training convection evolve. There will be multiple rounds of large-scale ascent that move through the region, which will favor a few windows of convection that look to remain loosely organized. Thus, it remains very difficult to pinpoint where any axis of training convection could set up and bring possible urban flooding concerns, so have opted to hold off on a Flood Watch. Expect at least 0.5-1 inch of rain late tonight through Sunday. Locally higher totals if we get into a training scenario with embedded thunderstorms.

Early next week, high pressure moves in behind the departing system and we should have a few drier days with seasonable temperatures in the lower 80s. With warm air advection moving back into the region ahead of another system tracking east across the upper great lakes and central Canada, we should see a gradual warming trend through mid to late week.

MARINE

Northeast flow picks up across the central Great Lakes tonight and especially Sunday afternoon as a low pressure system over the lower Ohio Valley lifts northeastward. Strongest flow will channel across Saginaw Bay leading to Small Craft Advisory conditions. Similar concerns for the rest of the Lake Huron nearshore, but will reconsider an extension with the evening update. Chances for rain and thunderstorms continue through the remainder of the weekend as the low and its associated frontal features approach. Isolated storms could produce locally strong winds and elevated waves today through Sunday. High pressure influence becomes entrenched across the region Monday offering drier weather and weaker winds, with headline-free conditions.

HYDROLOGY

Scattered to numerous showers with embedded thunderstorms are forecast this afternoon into Sunday. Heavy rainfall rates are still possible, especially with any thunderstorm activity. Localized rainfall totals may exceed 2 inch where persistent training convective activity develops. This may lead to isolated flooding concerns this weekend, particularly in urban areas.

PREV DISCUSSION

Issued at 1253 PM EDT Sat Aug 1 2026

AVIATION...

A large low-pressure system sits over the western Ohio Valley this afternoon, with light easterly winds over southeast Michigan drawing in some drier mid-level air. Nonetheless, diurnal instability will likely trigger showers and possible thunderstorms, with the best chance near the I-69/M-59 corridors. Otherwise, mainly just some high based light showers around. Heavier shower activity will result in lower cigs (MVFR) for a period. Tonight, the focus shifts to the southern tafs as the main moisture plume from the Ohio Valley storm system reaches the southern Michigan border. A prolonged period of showers and at least MVFR cigs expected for DTW-YIP-DET late tonight into Sunday morning. Embedded thunderstorms will be possible just about any time during this window, but are highlighted between 10- 14z with a prob30. Despite fewer showers across northern tafs tonight/Sunday Morning, MVFR cigs are also likely to develop with the persistent flow off southern Lake Huron. Northeast winds with gusts aoa 20 knots are expected during the day on Sunday.

D21/DTW Convection... There is a low chance of thunderstorms from late afternoon through the evening, with a continued chance tonight within an area of heavier showers that continues through Sunday morning.

DTW THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less late today and this evening. Moderate to high tonight and Sunday.

* Low for thunderstorms through taf period.

DTX WATCHES/WARNINGS/ADVISORIES

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