textproduct: Detroit/Pontiac

KEY MESSAGES

- The Heat Advisory is in effect until 8 PM.

- EGLE has declared an Air Quality Alert today and extended it through Thursday due to Canadian wildfire smoke reaching the surface and the resultant rise in PM2.5.

- There is a slight chance for a stray shower or thunderstorm this afternoon and evening.

- Increasing chances for showers and thunderstorms Friday through the weekend.

DISCUSSION

The southward advancing smoke plume remains the weather highlight in this update. Afternoon satellite and surface observations indicate the leading edge of denser smoke near the I-69 corridor at forecast issuance, tracking closely with the southward progress of the surface cold front. Model timing adjusts the leading edge timing down to the Ohio border closer to midnight. The Air Quality Alert is in effect now through tonight.

The timing of the front and advancing smoke has allowed most locations outside of the northern Thumb to warm up into the lower and mid 90s, with lower to mid 70s Td carrying heat index into the advisory range above 100. The Heat Advisory has been cancelled for the Thumb but remains in effect until 8 PM for the rest of SE Mi. The heat and humidity have also built up an impressive amount of potential instability as hourly mesoanalysis shows MLCAPE climbing into the 2000-2500 J/kg range. This has so far been held in check by a fragile capping inversion in the 850-700 mb layer. HREF and REFS mean QPF suggest holding on to an isolated mention through the evening with a few individual members showing initiation post 00Z.

Dry weather later tonight and in the morning allows wildfire smoke to burrow into the region. Impressive persistence of the plume through Thursday is shown in today's HRRR model runs of near surface smoke density over the Great Lakes. Values observed today across the northern Great Lakes are projected to hold over all of Lower Mi Thursday and Thursday evening prompting extension of the Air Quality Alert. The smoke is shown to be strongly confined within the stable boundary layer within the area of surface high pressure covering the region. There is some potential for deeper boundary layer mixing in forecast soundings Thursday afternoon which aids in slowly decreasing concentrations late in the day and Thursday evening. Conditions are dry otherwise as the band of mid/upper level clouds currently over the northern Great Lakes settles southward with less coverage. Cooler temperatures are the result when combined with the smoke layer and northerly wind limiting factors that hold high temperatures in the mid to upper 80s, toward the lower end of guidance ranges. Less humid air is also inbound post front carrying surface Td down to around 60 by Thursday morning where it holds through the day.

High pressure holds dry weather over the central Great Lakes for the bulk of Thursday night while the next low pressure system organizes in the northern Plains. This system initiates an active period of showers and thunderstorms beginning with accelerated moisture transport ahead of an inbound warm front Friday. Weekend time range models then show the low moving across the northern Great Lakes followed by the trailing cold front that is shown to be on the active side while moving through Lower Mi.

MARINE

A weak backdoor cold front continues south across the central Great Lakes today and is approaching Lake St. Clair. This allows winds to eventually veer toward the north-northwest behind the front. Wind speeds still only top out around 20 knots through this evening, more so over the northern half of Lake Huron where the post-frontal gradient is a bit stronger. Dense smoke due to Canadian wildfires is spreading southward in the wake of the boundary, and is expected to continue into the overnight hours. Therefore, expanded the Dense Smoke Advisory to the rest of Lake Huron and also Lake St. Clair. May need another extension for Lake Erie depending on where the front ends up later this evening.

A couple pop-up storms are still possible along the frontal boundary and/or lake breeze development late this afternoon and early evening. The probability of severe weather with any isolated storms is low. North-northwest winds at or below 20 knots expected again Thursday afternoon with the higher values over the northern half of the Huron basin. Forecast confidence breaks down over the weekend due to conflicting model guidance regarding the location and magnitude of a weak surface low passing through Lower Michigan, which will impact wind trends and thunderstorm potential. Prevailing winds should generally remain below headline criteria through the forecast period, with one exception being marginal Small Craft Advisory gusts over Saginaw Bay and/or The Thumb nearshores Saturday afternoon.

PREV DISCUSSION

Issued at 141 PM EDT Wed Jul 15 2026

AVIATION...

A cold front eases southward across SE MI this afternoon and evening as weak high pressure builds into the northern Great Lakes. As moisture and instability pool south of the front, there will be a slight chance for isolated convection in the KDTW and KYIP vicinity, so have maintained the PROB30 for thunder. Of more widespread aviation concern will be the plume of near-surface wildfire smoke that continues to advect south behind the front through tonight. An extended period of visibility restriction will accompany this smoke which has potential to linger into the late week. Will highlight MVFR conditions through tonight, but forecast adjustments will be governed by short-term trends as this scenario carries low predictability in flight category and longevity. Light northwest wind weakens and veers northeast tonight before emerging from the northwest again on Thursday.

D21/DTW Convection...Isolated thunderstorms may develop across central and southern portions of the airspace this evening, centered between 00Z and 03Z.

DTW THRESHOLD PROBABILITIES... * Low for thunderstorms this evening.

* Medium for ceiling/vertical visibility at or below 5000 feet tonight.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Heat Advisory until 8 PM EDT this evening for MIZ047-053-060>063- 068>070-075-076-082-083.

Lake Huron...Dense Smoke Advisory until 10 AM EDT Thursday for LHZ361>363-421- 422-441>443-462>464.

Lake St Clair...Dense Smoke Advisory until 10 AM EDT Thursday for LCZ460.

Michigan waters of Lake Erie...None.