textproduct: Detroit/Pontiac

KEY MESSAGES

- A few lingering showers are possible early Wednesday, then turning mainly dry through the end of the week.

- The next chance for showers and storms arrives Friday night, continuing into Saturday.

DTW THRESHOLD PROBABILITIES

* Medium for ceiling at or below 5000 feet tonight, and high later this morning.

* Very low for thunderstorms through the early morning hours.

PREV DISCUSSION

Issued at 347 PM EDT Tue Aug 18 2026

DISCUSSION...

Surface high pressure influence exits this evening as a cold front continues to advance toward Lower Michigan tonight. A disjointed line of showers and thunderstorms currently positioned along the front should persist and grow in scale as the boundary approaches Southeast Michigan. This results in a period of nocturnal convection which should become more organized as the evening wears on, possibly containing some multicell clusters and linear segments. One limiting factor will be timing since the diurnal cycle will have already peaked, but regardless, low-level CIN should inhibit the path of most surface-based parcels. Aloft, mid-level lapse rates are more supportive of instability, but with limited density as MUCAPE values should only reside within the 200-500 J/kg range. SPC's latest SWODY1 added a Marginal Risk to more of Lower Michigan, extending all the way across The Plains, and up into Montana. Main concern will be a rogue downdraft or two, resulting in a low-end chance for isolated marginally severe gusts. Machine learning datasets are mixed on any severe potential.

The front slows Wednesday, becoming quasi-stationary over the Ohio Valley as the governing longwave composite trough axis aloft becomes stalled. The placement of the surface convergence zone favors a mainly dry forecast for Wednesday, after any morning remnants clear south. The post-frontal airmass will only be slightly cooler, hindered by unfavorable WNW flow trajectories that delay the onset of more robust cold advection. Some evidence of a secondary weak backdoor cold front trying to move in off Lake Huron, but diffuse pressure field limits the cohesiveness of a material northeasterly wind shift. Between the backdoor front over The Thumb, and the stalled boundary just to the south, potential exists for additional convection Saturday. The 12Z HRRR is the most aggressive CAM in generating Wednesday afternoon convection along/north of I-69, although it's in the extreme minority as NBM PoPs are about zero between 18Z and 00Z Wednesday. Note that the 18Z HRRR fell in-line with the rest of the Hi-Res space. Mid-level perturbation within the mean flow does offer weak synoptic support. Areas to the far south may see diurnal convection spill just north of the Michigan/Ohio state line. No severe weather expected with any conditional convection Wednesday.

Surface high pressure attempts to build more aggressively into Lower Michigan on Thursday, in spite of persistent vicinity longwave troughing. Lower column stability/drying and subtle warming aloft make for a difficult setup for any shower activity to materialize. Temperatures persist near or a couple degrees above normal, in the lower 80s. The next chance for showers and storms arrives Friday night, continuing into Saturday as the next wave digs across the High Plains toward the Ohio Valley. Thermal troughing fills in afterwards, delivering slightly cooler than normal conditions into early next week as 700 mb temperatures dip near/below 0C.

MARINE...

A cold front will pass from north to south across the Great Lakes this evening and into the early morning hours which will veer wind direction from southwest to northwest. Showers and thunderstorms will be likely with the passage of the front. There will be a low chance for a stronger isolated thunderstorm capable of producing a wind gust aoa 34 knots. This will be most favorable across Lake Huron.

High pressure fills back in behind the front which will maintain lighter wind speeds through Thursday. Additional chances for showers and storms will return Friday into the weekend with the passage of a warm and subsequent cold front.

DTX WATCHES/WARNINGS/ADVISORIES

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