textproduct: Detroit/Pontiac

KEY MESSAGES

- Scattered thunderstorms develop overhead this afternoon and evening. Isolated severe storms will be possible.

- Mainly dry conditions develop Thursday through most of Saturday.

- Renewed chances for showers and thunderstorms late Saturday into Sunday.

DTW THRESHOLD PROBABILITIES

* High for ceiling 5000 feet or less tonight and Thursday.

* Low for thunderstorms this evening.

PREV DISCUSSION

Issued at 350 PM EDT Wed Aug 12 2026

DISCUSSION...

The Great Lakes and Ohio Valley remained locked into an unsettled deformation pattern again today, which steered yet another MCS across the Ohio Valley. A lackluster showing locally with just a brief flare up in shower activity near the state line already decaying at issuance. That said, composite reflectivity does show outflow emanating north from the complex which will be one of several small-scale forcing mechanisms capable of triggering additional convection this evening.

Stable but moist low levels characterize the airmass across the southern counties where surface dewpoints are near 70 degrees. Delineation in cloud cover throughout the day has set up an impressive differential heating boundary around the I-94 corridor. Temperatures underneath the stratus deck are only in the low 70s compared to low 80s in partial sun to the north. With 6.0-6.5 C/km mid level lapse rates present across all of SE Michigan, instability is tied to the moistened boundary layer conditions which are most favorable where rain fell earlier today across the Saginaw Valley/Thumb region and near the Lake Huron shoreline. This also happens to be where the nose of an upper level jet will connect with low level troughing to present a more focused area of weak ascent this evening.

Current satellite trends show a few spots where towering cumulus is attempting to gain traction, mainly along the lake breeze influence from Bad Axe south. The existing stable layer is still broadly preventing deep convective growth, as has been the case the past several days, although a couple of deeper cores have developed along the interacting lake breeze boundaries. Expectation is for the arrival of the synoptic ascent and lake breezes/outflow to piece together enough ascent for more updrafts to break through the cap. Thus additional convection development is expected overhead through the evening (roughly 22z-03z or 6pm-11pm EDT). This will mainly occur north of the M-59 corridor where instability is most favorable. The deepest updrafts will have access to ~40 knots of 0- 6km bulk shear and cape density throughout the mid-levels. Isolated storms will thus be capable or 1+ inch hail and downbursts of 60+ mph. SWODY1 continues to highlight a Marginal Risk for much of the area.

Low confidence pattern lingers through the rest of the week into the weekend as the deformation axis loiters over the Ohio Valley. Disjointed moisture and weak forcing will continue to struggle generating convection, while a southward shift in the boundary Thursday favors a dry forecast for all of SE Michigan. This boundary does attempt to lift back north Friday-this weekend, but will be competing with high pressure over Ontario which keeps better moisture/instability to our south and west. Upstream convection may still have an impact on cloud cover, while residual low level moisture affords fog chances again Thursday morning--both influencing temperatures.

Relief from this unsettled pattern finally arrives late this weekend- early next week as low pressure ejects out of the northern Rockies into Canada. This drives a cold front across the Upper Midwest and Great Lakes which brings an increased chance of showers and storms this weekend, but a bout of high pressure behind it. Seasonable temperatures in the low-mid 80s are expected throughout the 7-day forecast period.

MARINE...

A stalled front near the southern Michigan border will continue to be a focus for multiple rounds of thunderstorms over the next couple days. Lake St Clair and Lake Erie have the highest chances of convection affecting them being closer to the stalled front, but periodic chances will continue further north as well. Outside of any convection, high pressure to the north of the front will provide generally light northwesterly winds through Thursday at 10 knots or less. With the lighter winds, there are some weak signals for patchy dense fog over Lake Huron at times, through confidence remains low. On Friday, the high pushes eastward across the central and eastern Great Lakes which will favor an uptick in northeast winds. Winds then turn southerly late Saturday and increase to around 20 knots ahead of a cold front Saturday night.

DTX WATCHES/WARNINGS/ADVISORIES

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