textproduct: Detroit/Pontiac

KEY MESSAGES

- Multiple rounds of showers and a few thunderstorms are forecast Saturday and Sunday.

- Heavy rainfall is likely somewhere over northern Indiana, southeast Lower Michigan or northwest Ohio Saturday night and Sunday morning. 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 much of next week with chances of showers and seasonable temperatures.

DTW THRESHOLD PROBABILITIES

* Moderate for ceiling 5000 ft or less late tonight and Saturday.

* Low for thunderstorms Saturday afternoon

PREV DISCUSSION

Issued at 239 PM EDT Fri Jul 31 2026

DISCUSSION...

Last vestige of the quiet and dry conditions remain in place over southeast MI this afternoon and surface high slides to the east. Although, there may be a shower near the Lake Huron lake breeze late this afternoon and early evening. Region's weather will be increasingly influenced by a few upper waves from IL extending southwest, all in advance of the main upper low over southern MN/northern IA.

Clouds increase this evening ahead of these features first, and then enough moisture advection in the mid layers with one of those waves in the southwest flow will bring chances of showers and slight chance of thunderstorms around and after midnight for the northwest half of the forecast area...mainly northwest of a OZW to Sandusky line.

The forecast area will continue to be on the edge of the best forcing of the upper trof on Saturday as a cold front slides across northern MI. A surface low will move into IN in response to the upper trof with a warm frontal feature extending to the east into OH. Closer to these surface and low level forcing features will be the best chances of showers and a few thunderstorms to develop and will have the highest POPs in the Tri Cities and down near the OH border. Regardless, it will be cloudy and humid with temps below late July averages.

The real impact part of this system occurs Saturday night and Sunday morning as the upper trof moves over MI, IN and OH. PWAT increases to 1.75+ inches. Mid layer instability increases with around 500 J/kg available, enough for convection and a chance of thunderstorms. All of these environmental conditions will be greater over northern IN, far southeast Lower MI (ARB to PHN on south) and NW OH. The question for the heavy rain potential will be where exactly the deformation axis setup a potential SHARS type of rainfall event. Model camps are split across the MI state line, but the potential is high enough to start messaging the heavy rain threat through DSS channels. Will hold off on any Flood watches since the peak of the event is still around 36 hours away to allow for some consensus on that deformation axis to setup.

By Sunday afternoon, the system is slowly moving east and expect some improving conditions. Those will range from partial clearing in Midland County to the ending of the showers in Detroit and Monroe.

The extended forecast is looking a little more unsettled for next week. That upper trof now looks to cutoff over the Upper OH river valley on Sunday night and Monday. While we will be far enough away on Monday to be dry with partly sunny conditions, the cutoff low will slowly migrate north on Tuesday and Wednesday bringing some chances for mainly diurnal showers. Later Wednesday into Thursday, the next wave and cold front settle through Lower MI and stalls near the southern border with additional waves in the zonal upper flow. This will bring some periodic chance for showers and storms late next week. All of this will have temps at or below early August averages.

MARINE...

High pressure that has influenced the region over the past few days will continue to track off to the east this afternoon. Quiet marine conditions will continue through this afternoon for the eastern Great Lakes. Lighter winds overnight will slowly increase and turn northeasterly Saturday as a low pressure system currently over the upper Mississippi River Valley shifts eastward towards the Ohio Valley. With the northeast winds, this will lead to increasing waves through the Saginaw Bay this weekend. There will be chances for showers and thunderstorm later tonight through Sunday as the low and frontal features push across the region.

HYDROLOGY...

Scattered to numerous showers with embedded thunderstorms are forecast late Saturday into Sunday as a low pressure system tracks into the Ohio Valley. The increasingly moisture laden environment will support moderate to heavy rainfall rates. There is relatively high confidence in rainfall totals between 0.25" and 0.75". Considerable uncertainty exists regarding placement and magnitude of the heaviest rainfall, but low probability (<30%) exists for rainfall totals in excess of 2.00" by late Sunday. This may lead to flooding concerns this weekend, particularly in urban areas.

DTX WATCHES/WARNINGS/ADVISORIES

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