textproduct: Detroit/Pontiac

KEY MESSAGES

- Isolated to scattered shower chances mainly north of I-69, particularly in the Thumb, this evening-early tonight as a cold front crosses.

- Dry, seasonably average conditions for the early week period.

- Shower and storm chances return Tuesday night into Wednesday with the arrival of the next cold front.

DISCUSSION

The chance for isolated to scattered showers with a low chance for an isolated thunderstorm will continue through the evening hours with the passage of a cold front. Passage of this front to take place around 22Z - 02Z, with all precipitation chances ending thereafter. Weaker forcing will limit coverage, with hi-res output highlighting the Thumb region as area with slightly better coverage potential tonight. Skinny and long CAPE with values between 1000- 1200 J/kg, warm cloud depths around 12kft and PW values above 2" will still bring chances for heavy downpours with any more robust activity.

Filling in of low stratus will be increasingly likely overnight across the Thumb through the Irish Hills with the veering of low- level flow to the north. Diffuse region of high pressure in the wake of the front under zonal flow with daytime mixing will work to scour out cloud cover through the morning/afternoon tomorrow as daytime temperatures return into the low 80s. Temperatures holding in the upper 70s will be possible with any pronounced stratus that lingers through the early part of the day. Dry conditions continue through at least the afternoon on Tuesday before a second weak cold front expands across SE MI. Passage of this front is expected around of after 00Z Wed and will progress across southern Michigan through 09Z. This will bring renewed chances for rain showers and embedded thunderstorms.

A slightly more tangible temperature response is expected after the passage of this front noted by temperatures highs in the upper 70s on Wed and Thu. Decreasing humidity is also expected to continue to work in behind the front with dew points dropping into the 50s by Thursday afternoon. Confidence decreases Fri-Sat regarding timing of rain chances, again which will likely be derived from another cold front. Timing of frontal passage will be contingent on progression and strength of upper-level waves across central and northern Canadian Provinces.

MARINE

Area of low pressure passing north of the region will pull a cold front through the area this afternoon and evening. The winds, currently southwesterly, will flip around to the northwest while increasing to 15 to 20 knots with gusts to 25 knots across Lake Huron. The increased northwesterly winds will reach Lake St Clair and Lake Erie tonight but gusts should only top out in the 15 to 20 knot range. The winds tonight will cause waves to increase up to 5 feet in the nearshore zones of Lake Huron thus a Small Craft Advisory has been issued tonight into Monday morning. Showers and thunderstorms will be possible along and ahead of the front which should end by midnight tonight. High pressure then builds in behind the cold front Monday through most of Tuesday keeping the northerly flow but at tempered speeds. Next chance of thunderstorms comes late Tuesday with the next cold front.

PREV DISCUSSION

Issued at 145 PM EDT Sun Aug 16 2026

AVIATION...

Convective system was exiting southeast Michigan with the bulk of the showers east of the TAF sites. There remains a chance of showers through the afternoon and early evening between that system and the cold front across the Straights area. Plenty of low level moisture this afternoon with MVFR ceilings across most of Lower MI are ever so slowly lifting with some breaks in the clouds. Expect only slight improvements for the rest of the afternoon. Will keep most areas MVFR ceilings although there could be brief periods of VFR ceilings.

Once the front moves through the region between 00z and 06z, winds turn from the west and become northwest or even NNW generally 5 to 10 knots. This wind should be enough to keep fog from forming. There could be a brief break in the clouds, but there is low level moisture to bring back ceiling between 1k and 2k feet after 06z. This cloud deck lifts to a bkn cumulus ceiling around 3k feet Monday morning.

D21/DTW Convection...Very low chance for thundestorms through early this evening.

DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 feet through the overnight.

* Low for thunderstorms this evening.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory from 10 PM this evening to noon EDT Monday for LHZ421-441>443.

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