textproduct: Detroit/Pontiac

KEY MESSAGES

- Heat builds during the early half of the week with highs in the mid to upper 90s through Wednesday.

- Peak heat expected Tuesday with highs in the upper 90s and heat indices near or above 100 degrees. A Heat Advisory has been issued for all of Southeast Michigan Noon to 8pm Tuesday.

- Potential for showers and thunderstorms exists late in the week into next weekend.

DTW THRESHOLD PROBABILITIES

* None.

PREV DISCUSSION

Issued at 250 PM EDT Mon Jul 13 2026

DISCUSSION...

Mid-upper ridging across the north-central Plains has begun the process of folding into the central Great Lakes today supporting widespread highs in the lower 90s. A notable uptick in humidity accompanies this airmass as the resident upper 50-lower 60 dewpoints are replaced by upper 60s-lower 70s pushing heat indexes firmly into the mid/upper 90s. This also leads resultant overnight lows to only fall to around 70.

600dam ridge axis is fully folded into southern lower MI drawing the core of the upper Plains heat dome overhead with local 850mb temps making a run near 25C by late morning. Active subsidence combined with elevated warm advection sets up a strong inversion between 4- 6kft firmly capping the region for any pop-up convection. Main update with this forecast package was to flip the current Extreme Heat Watch to a Heat Advisory for Tuesday afternoon-evening. While the NBM continues to remain bullish on highs in the low 100s, local probabilistic guidance has been more muted instead favoring upper 90s which shifts peak heat indices from the mid 100s to closer to 100-105 range. Given the performance from earlier heat waves this summer, am skeptical of the magnitude of the NBM actual/apparent temperatures especially as diving into historical climo data for DTW/FNT/MBS only shows the sites hitting warning criteria (105F heat index) 15-19 days since 2000. While can't rule out a few locations within the Saginaw Valley or Metro Detroit touching 105F heat indices, not expecting the 3 hour duration to warrant a warning over an advisory.

Still hot again Wednesday though with the mid-level ridge axis now directed into the Ohio Valley by this point, the core of the airmass is likewise shifted towards northern OH/far southern SE MI. Areas south of M-59 likely still see highs in the upper 90s with areas north falling closer to the mid 90s as a weak cold front sags south. In a similar vein to Tuesday, some of these southernmost locales could see heat indices touch 105, however duration is expected to fall short with 100-105 forecast to be predominant. For areas, north heat indices looking to top out around the 95-100 degree range. At least portions of the CWA will require another Heat Advisory however will take headlines day by day.

Late week is marked by continuing southward compression of the mid- level ridge by troughing across the Hudson Bay/eastern Canada. SE MI looking to reside on the northeast fringe which offers a chance at near advisory heat indices, at least for urban areas, though also begins to open the door for embedded shortwaves to clip the region particularly Friday into the weekend as ridging breaks down and cyclonic return flow develops. Any potential convection/MCS tracks are highly dependent on the exact compression of the ridge which carries low confidence this far out.

MARINE...

Hot airmass (850 mb temps in the mid-twenties) will track into the Central Great Lakes from the northwest through tomorrow, leading to stable low level profiles. This should hold the max westerly winds in the 20 to 25 knot range, with the highest winds across northern third of Lake Huron due to the channeling through the straits. A mainly dry backdoor cold front dropping south Tuesday night into Wednesday will allow winds to veer to the northwest behind the front, but still only topping out around 20 knots Wednesday evening over the north half of Lake Huron. Northwest winds at or below 20 knots holds on Thursday. The forecast on Friday and Saturday unravels due to conflicting model guidance regarding the location and magnitude of a surface low moving through the Great Lakes region. This has significant impact not only on wind speeds, but also on wind direction, along with bringing chances of showers and thunderstorms.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Heat Advisory from noon today to 8 PM EDT this evening for MIZ047>049-053>055-060>063-068>070-075-076-082-083.

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