textproduct: Detroit/Pontiac

KEY MESSAGES

- A dry period is expected tonight into tomorrow.

- Widespread showers and possible thunderstorms return Saturday into Sunday. Rainfall totals in excess of half an inch are likely, with the potential for 1 inch or more.

DISCUSSION

Greater subsidence arrives this afternoon and has brought an end to the main area of showers, but some isolated light rain/drizzle remain this afternoon. While showers largely come to an end, expect cloud cover to linger into the evening especially along and south of I-69. At least some low chances to see a stray shower along the southern border tonight as the stalled frontal boundary lingers across northern IN/OH. Cooler northerly flow will be drawn into the area tonight by a surface high moving into Ontario. This will help bring morning overnight lows tonight down into the upper 40s across parts the far northern CWA in the Saginaw Valley and maybe parts of the Thumb.

This surface high center will slide east into Quebec into tomorrow and be the influencing feature that will result dry conditions tomorrow. Southern extension of the thermal trough with surface flow out of the N-NE will bring daytime highs right around seasonal normals in the mid 70s for most of southeast Michigan with around 70s across the northern portions of the Thumb.

A plume of deep moisture will then be drawn into Michigan late Friday and Saturday around the broad southeast CONUS ridge. Theta-e ridge lifting into the region will contain PWATs of 1.50 inches to 1.75 inches or greater. Increased flow under right entrance jet dynamics will help support larger scale synoptic lift northeast of a developing trough across the plains. This will lead to an area of showers and thunderstorms upstream across the western Great Lakes states that will begin to move into southeast Michigan late tomorrow night and across all of southeast Michigan Saturday. Likely showers blanket the majority of southeast Michigan by late Saturday morning with a chance of thunderstorms mainly south of I-69. Instability is forecast to be rather weak keeping severe potential limited, but some isolated embedded thunderstorms will be possible as bulk of activity arrives during the day. Main concern for Saturday into Sunday will be the heavy rainfall potential. Ensemble space still supports a swath of 24 hour QPF of 0.75 to 1.5 inches Saturday 12Z to Sunday 12Z. Some of the recent hi-res guidance is allowing for a little bit of a break in heavier precip potential late afternoon into early evening as lead wave of showers and possible thunderstorms weaken upon arrival before additional activity reinvigorates along the frontal zone Saturday evening into Sunday. The swath of heaviest precipitation has shifted a slightly and is now focused along and west of I-75 from Saginaw south to the greater Detroit metro region. A Slight Risk for Excessive Rainfall remains in place for much of southeast Michigan. Precipitation chances continue into Monday with greater uncertainty in precipitation chances into the middle portion of next week.

MARINE

Winds remain on the lighter side (<20kts) through the evening as the southern edge of northern Ontario high pressure slides overhead. A secondary cold front drops through the region tonight-Friday with the main impact being a modest uptick in northeasterly winds (toward 20-25kts) over the southern half of Lake Huron. Onshore flow likely will warrant a period of Small Craft Advisories along the Thumb Friday. This front stalls over northern Ohio before attempting to lift back north Saturday as Plains low pressure arrives. Front looks to only push north of the southern Great Lakes before the system tracks over lower MI resulting in predominant east-southeast turning northeasterly winds this weekend. Widespread showers and scattered thunderstorms are possible, mainly focused over the southern half of the region. A moderate gradient, supporting NE/E gusts 20-30kts, lingers behind the low Sunday into the new work week as the area holds between the stalled boundary over the Ohio Valley and high pressure over northern Ontario.

HYDROLOGY

A low pressure system approaching from the plains with increasing deep moisture will bring a pattern of heavy rain beginning early Saturday into Sunday. Expecting a widespread steady rain starting Saturday morning with scattered embedded thunderstorms. A high probability exists for a swath of total rainfall between a half inch to 2 inches over the course of Saturday and Sunday with a low chance for some areas to see between 2-3 inches in a 24 to 36 hour period. A potential lull in heavier precipitation Saturday evening brings some uncertainty to overall impacts, but there will be a chance for flooding potential of low lying areas and urban areas, especially if the higher amounts occur over a shorter period of time.

PREV DISCUSSION

Issued at 112 PM EDT Thu Sep 17 2026

AVIATION...

A stalled frontal boundary and large swath of low-level moisture holds across southern Michigan which has produced an extended period of IFR cigs from KFNT south. Latest trends show high pressure north of this low level moisture working southward, which will result in gradual lifting of ceiling heights and slow dissipation of cloud cover. Improving trends will take place from north to south and initially has been slow to start, so have delayed improvement to VFR conditions several hours until the evening hours, allowing the dry air time to work into the region. High pressure will initially strengthen the pressure gradient which will see a very subtle increase in north to northeast flow as cig conditions improve.

D21/DTW Convection...Thunderstorms are not forecast today or tonight.

DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft this afternoon and evening.

DTX WATCHES/WARNINGS/ADVISORIES

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