textproduct: Detroit/Pontiac

KEY MESSAGES

- The Air Quality Alert remains in effect through Saturday due to persistence of wildfire smoke causing hazardous air quality.

- Improvement of smoke concentration begins tonight as wind shifts SW after passage of a warm front.

- Isolated coverage of thunderstorms later this afternoon and tonight. Severe intensity is not expected. - There is a Marginal to Slight Risk of severe intensity thunderstorms as coverage becomes numerous Saturday afternoon and evening.

- Dry weather with cooler temperatures and lower humidity moves in by Sunday.

DTW THRESHOLD PROBABILITIES

* Moderate in ceilings aob 5000 feet this evening. Low tonight and moderate on Saturday.

* Moderate in thunderstorms this evening and moderate Saturday afternoon.

PREV DISCUSSION

Issued at 350 PM EDT Fri Jul 17 2026

DISCUSSION...

A mid-level trough passing from Manitoba into northwestern Ontario is driving the development of a surface low that will affect local conditions tonight into this weekend. Its warm front is analyzed from the western UP down to southern Lake Michigan this afternoon, and will continue to progress northeast through the evening into tonight. The bulk of forcing for ascent will be tied to height falls farther north, but as the front and moisture axis push through SE MI there should be enough surface convergence and unbalanced flow aloft to trigger scattered showers and isolated storms later this afternoon and evening. Can't rule out a stray stronger downburst wind, but in general poor lapse rates and bulk wind shear aob 30 kt will limit storm organization and strength. Slow storm motion brings potential for pockets of heavier rainfall. Available smoke model guidance does suggest gradually improving air quality conditions tonight as southwest wind ushers out the worst concentrations of the wildfire smoke. This improvement likely continues through early Saturday with prevailing wind direction remaining out of the southwest.

The surface low treks across Lake Superior tonight then north of Georgian Bay into Quebec by tomorrow afternoon, its cold front lagging behind and passing through the local area during the peak in the diurnal cycle. It is unclear whether nocturnal convection will hold together across northern lower during the morning hours, but given strong frontal forcing the bulk of CAMs do support convective initiation or reinvigoration across SE MI between noon and 4pm. HREF and REFS ensemble progs highlight SBCAPE of 2000 to 2500 J/kg and bulk wind shear of 25 to 30 kt increasing to around 40 kt as the upper jet works south. This supports a band of more organized convection with potential for stronger to severe storms. The bulk of the shear will be within the lowest 0-3km which favors damaging wind gusts as the main threat - this is corroborated by available hi-res severe ML guidance. There is a secondary threat of large hail and an isolated tornado if any discrete supercellular structures develop, but this potential remains low. With PWAT increasing near or above 1.75" any storms will be capable of producing heavy downpours, but progressive storm motion will limit a greater flooding threat. Storms are expected to exit south to Ohio and Lake Erie by late afternoon with drier air then filtering in behind the cold front. Descending parcel trajectories originating from the northern Great Lakes will bring potential for the return of surface-level wildfire smoke, but there is considerable spread among the latest solutions regarding PM2.5 concentration.

High pressure builds directly into the region on Sunday, promoting a dry and more comfortable day with highs in the lower 80s. Trends in the smoke plume will need to be monitored, but northeast wind early in the day suggests arrival of cleaner air from eastern Ontario. Monday sees the return of southwest flow as the high departs east. A shortwave dives across the Great Lakes Monday night into Tuesday, bringing the next likely round of showers and thunderstorms. An active pattern is possible through the rest of the week as a ridge amplifies over the western CONUS, leaving the Great Lakes within northwest flow with multiple rounds of shortwave activity.

MARINE...

Still monitoring upstream convection associated with weak low pressure systems approaching northern Lower Michigan and the lower Ohio Valley. Some of this activity should reach Lake Huron late this evening and early tonight. Latest Hi-Res models indicate a weakening trend for these showers and thunderstorms, once they reach the waterways. A warm front lifts into the central Great Lakes this evening and overnight marking a south-southwesterly wind shift which pushes the wildfire smoke plume back into Canada, improving visibilities. A secondary, and more robust, low pressure system passes through The Straits and across northern Lake Huron Saturday morning. This drags an attendant cold front through the region with time, causing winds to veer northwesterly. Pre-frontal (southwesterly) gusts over Saginaw Bay are now expected to exceed 25 knots, therefore a Small Craft Advisory is in effect. Extensions are possible for the rest of the Lake Huron nearshores with later updates to account for stronger post-frontal gusts during the afternoon hours. Additionally, isolated brief gusts to gales cannot be ruled out over central Huron later on Saturday, but confidence is too low for a Gale Warning. High pressure then builds back into the region late Saturday and Sunday supporting drier conditions and prevailing winds below headline criteria for rest of the weekend.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Dense Smoke Advisory until 10 PM EDT this evening for LHZ362-363- 421-422-441>443-462>464.

Small Craft Advisory from 3 AM Saturday to midnight EDT Saturday night for LHZ421-422.

Lake St Clair...Dense Smoke Advisory until 10 PM EDT this evening for LCZ460.

Michigan waters of Lake Erie...Dense Smoke Advisory until 10 PM EDT this evening for LEZ444.