textproduct: Detroit/Pontiac

KEY MESSAGES

- Warmer and increasingly humid Wednesday with afternoon/evening showers/thunderstorms; a few severe storms are possible.

- Lingering chances for a isolated shower Thursday afternoon, then turning cooler and drier through the first half of the weekend.

DISCUSSION

Low-level anticyclone and surface ridge depart this evening ahead of a shortwave descending on the Great Lakes region tonight into Wednesday. Temperatures should be bit a warmer overnight due to thickening cloud cover ahead of the wave, with lows in the upper 50s to around 60F.

Expect a dry start on Wednesday with strengthening gradient flow as winds back south-southwesterly. Pre-frontal/warm sector moistening will be ongoing, well ahead of the boundary, marked by a sharp increase in 925-700 mb ThetaE advection. The parent shortwave should slow upon arrival, once the vertically stacked low reaches Lake Superior by 12Z Wednesday. This slowing trend is supported in the 12Z model data leading to increasing confidence in a later start time for rainfall across most of Southeast Michigan. With the exception of the Tri-Cities, the rest of the forecast area should stay rain-free prior to 15Z, if not 18Z. Showers and thunderstorms should fire along the frontal slope once weak 800 mb (5 kft) capping erodes during the diurnal ramp-up. Non-convective gusts will mix down, occasionally reaching 25-30 mph.

A low-end severe risk exists Wednesday afternoon and evening as MLCAPE builds above 1000 J/kg, although 0-6 km shear only improves to 25-30 knots. SRH also isn't particularly impressive and struggles to break 100 m2/s2, but the longer that winds stay backed/southerly, the risk would increase for a low-end weak/short-lived tornado threat. The main concern should be for gusty/damaging winds. Latest SPC SWODY2 (Marginal with Slight south of I-96) appears to align well with a subset of latest ML data. Storm coverage should generally be broken/linear, positioned along the front, and ought to depart/conclude once the boundary exits by about 03Z. A weak secondary surface low may develop over The Thumb, and would offer rain potential into the overnight hours.

The shortwave will flatten and slowly get absorbed downstream into the larger-scale trough feature. Weak CVA could persist through Thursday, providing enough ascent atop shallow boundary-layer saturation to spur a few light showers/sprinkles, mainly during the evening hours. Surface high pressure builds in from the UP Friday with modest northerly flow helping limit highs to the upper 70s as 850 mb temperatures drop into the single digits (Celsius). The surface ridge exits into the eastern Great Lakes over the weekend with return flow shifting gradient winds southwesterly in advance of the next possible system.

MARINE

A high pressure system now centered over the Great Lakes will maintain light winds and dry weather through the evening. Southwest flow to become better established overnight through tomorrow as high pressure departs into the eastern Great Lakes. An approaching cold front will strengthen the pressure gradient ahead of the front, increasing wind speeds through the day tomorrow. Wind gusts of 20 to 25 knots will be likely across Saginaw Bay given the favorable fetch, where Small Craft Advisories are now in effect. Showers and thunderstorms will also become increasingly likely with the passage of the front, including a low chance for isolated strong thunderstorm development capable of producing winds gusts aoa 34 knots. Post-frontal northwest flow continues through Thursday along with low end chances for rain showers, with high pressure filling back in Friday and Saturday.

PREV DISCUSSION

Issued at 140 PM EDT Tue Aug 25 2026

AVIATION...

High pressure governs conditions today resulting in light and variable winds alongside dry conditions. Diurnal cu field has emerged, but looks to stay mostly SCT through the evening. Winds organize out of the south this evening and strengthen above 10 knots by Wednesday morning. A cold front approaches the airspace Wednesday, although thunderstorm chances look to hold off across Lower michigan until after 18z Wednesday.

D21/DTW Convection...No thunderstorms are forecast today through Wednesday morning. Thunderstorm chances then increase Wednesday afternoon and early evening as a cold front tracks across Lower Michigan. Strong to severe storms are possible.

DTW THRESHOLD PROBABILITIES...

* Medium for thunderstorms Wednesday afternoon-evening.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory from 10 AM to 10 PM EDT Wednesday for LHZ421- 422.

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