textproduct: Detroit/Pontiac

KEY MESSAGES

- Mainly dry today with a few isolated showers possible over the Thumb this afternoon.

- Scattered showers are possible Saturday morning, and then again Saturday afternoon.

- Broader coverage of showers and thunderstorms possible Sunday evening and overnight, especially south of I-94.

- Cooler than normal temperatures are expected through at least the middle of next week.

DTW THRESHOLD PROBABILITIES

* Low for ceiling at or below 5 kft this afternoon. Moderate toward sunrise Saturday.

PREV DISCUSSION

Issued at 400 AM EDT Fri Jun 19 2026

DISCUSSION...

The 990 mb surface low pressure system that produced active weather Wednesday into early Thursday will continue tracking eastward along the St. Lawrence river today, exiting into the Canadian Maritimes. Given its meridionally expansive cyclonic field, dynamic ascent will still be present over portions of Southeast Michigan. Forecast soundings indicate perhaps just enough mid-level cooling within the northwest flow regime to support weak SBCAPE, on the order of 100- 250 J/kg. This instability increases, just as mid-level geopotential heights reverse and begin to rise with the arrival of shortwave ridging. This should act to inhibit ascent, but chose to include mentions of isolated thunderless light showers across the greater Thumb region from 18-22Z. It's also possible that the dry column will favor virga with any showers that do materialize. Hydrometeors face a difficult path for survival, falling through a nearly 5 kft inverted-V shaped boundary-layer, so no QPF was added. Guidance continues to run a bit warm, relative to expected highs, given 850 mb temperatures around 8C. However, unimpeded insolation due to near zero cloud fraction should offer a diabatic boost. Highs in the low 70s ought to be the norm, with mid 70s possible from Metro Detroit south. Surface ridging briefly builds in early tonight, backing winds toward the WSW.

Low amplitude cyclonic shortwave perturbation embedded within the longwave pattern transits Lower Michigan early Saturday morning, along with a faint surface reflection. Residual Pacific moisture should suffice in the maintenance of remnant nocturnal convection, but this activity moves into a less favorable airmass. Much of the zonally advected theta-e will go towards top-down saturation of a column characterized by an initial PWAT of around 0.60 inches. While a morning lightning strike or two cannot be ruled out, forecast soundings are not supportive of meaningful shear or instability. The morning activity does improve antecedent conditions for diurnal convection Saturday afternoon. Showers and perhaps a few thundershowers are once again favored over the northeastern part of the forecast area (generally north of I-69), better positioned within the thermal trough aloft. Similarly cool and dry Saturday night with enough clearing and lows in the 50s.

Diffuse high pressure emerges over the lower peninsula Sunday morning while a speed max ejects across The Plains and into the Ohio Valley, likely sustaining an MCS. The time-frame for arrival is generally still out of the Hi-Res window, but mid-range 00Z deterministics largely agree in the shape and speed of this wave across the Ohio Valley. Main question now is how far north does the wave track, and by extension, how far into southern Lower does any isentropic/overrunning precipitation reach. The surface warm front will struggle to lift beyond the state-line, and low-level moisture transport will be fighting drier air filtering down from northern Manitoba high pressure. Latest PoPs appear a bit bullish at this juncture, particularly the Likelies north of I-94. Further south, the environment will be more favorable for higher rainfall amounts.

Cooler than normal temperatures are expected to continue through the middle of next week with drier conditions by Tuesday, followed by a showery day Wednesday.

MARINE...

West to northwest flow will hold today in the wake of a strong low pressure system which will support some breezy conditions for portions of the Great Lakes, particularly across northern Lake Huron given the more favorable fetch. A ridge of high pressure will build in tonight through tomorrow morning which will relax wind speeds and support lighter winds through the weekend. Rain showers will be possible tomorrow as an upper-level disturbance moves in, along with a low chance for an isolated thunderstorm. Additional chances for rain and thunderstorms will enter Sunday night to Monday morning as a low pressure system travels through the Ohio Valley and southern Great Lakes. This system will bring elevated wind gusts through Lake Erie and Lake St. Clair, where the pressure gradient is strongest.

DTX WATCHES/WARNINGS/ADVISORIES

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