textproduct: Detroit/Pontiac

KEY MESSAGES

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

- Peak heat expected Tuesday with highs in the upper 90s and heat indices near or above 100 degrees. An Extreme Heat Watch is in effect 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 304 AM EDT Mon Jul 13 2026

DISCUSSION...

Now-term trends concern ridge rider thunderstorm complex now tracking due southward over portions of the far eastern Lake Superior basin and the eastern Upper Peninsula. Subset of model guidance supports atypical due south to south southwest storm motion through the early morning with convection favoring the southern fringes of the CAPE reservoir that only bleeds down into northern Lake Michigan. Forward corfidi vectors definitely exhibit a westerly component with virtually no synoptic scale moisture transport or warm advection wave over Southeast Michigan. Forecast soundings support strong CIN throughout the lowest 13.0 kft agl. As a result, not expecting any convective activity to survive into the forecast area early this morning but did increase sky fraction. Will monitor.

Firm 600dam H5 ridge and heat dome is forecasted to fold into the central Great Lakes today and persist as a pseudo low amplitude Rex block through Thursday. Main weather forecast concern for the next few days will be the dangerous heat potential. Heat dome is forecasted to roll into the forecast area from the northwest today causing greatest heat indices approaching 100 degrees over the Tri Cities this afternoon. For today's setup there is some lower confidence regarding the surface dewpoints. Look of the NBM guidance suggests a possibility at too coarse of smoothing particularly in/near the Great Lake shorelines. With no fog this morning to potentially buoy surface dewpoints and limit mixing into the afternoon, the decision was to consider the greatest values as outliers. Did consider a Heat Advisory for the urban center of Saginaw County, however, given collaboration considerations and possibility that heat indices may only reach 100 degree for less than 3 hours did forgo the issuance. Temperatures are expected to drop into the lower to middle 70s tonight.

Centroid of midlevel ridge is forecasted to pivot directly across Southeast Michigan on Tuesday with warming aloft between 3.0 and 6.0 kft agl and 850mb temperatures close to 24C. With high probabilities of Wet Bulb Global temperatures exceeding 90 degrees and WPC HeatRisk outlining most of the area in Major risk decided to go with an Extreme Heat Watch for all of the counties Tuesday. Forecast soundings show active subsidence resulting in substantial capping inversion between 3.0 to 9.0 kft agl. Current heat indices forecast may be a touch high in a few locations as the capping inversion could limit mixing depths. Will probably go day by day with heat headlines this stretch with heat indices forecasted to drop into the lower to middle 70s again Tuesday night.

Heat dome then gets progressively compressed to the south for Wednesday and Thursday. Still looking at hot and humid conditions with temperatures for many areas in the 90s and dewpoints in the 60s. Additional heat headlines may be needed particularly for urban centers. Still summer warmth across the Thumb even if a weak backdoor front pushes inland off of Lake Huron.

Broad troughing over northeast North America may work into Southeast Michigan from the north for the end of the week and the upcoming weekend. Important to stress very low confidence in the timing and duration of rain and thunderstorms as the MCS track could come into range. The exact sensible weather forecast would come down to the exact placement of the edge/fringe of capping and instability.

MARINE...

High pressure will continue to hold over most of the Great Lakes region today and going into the beginning of the week. The one caveat will be across northern portions of Lake Huron where there may be some lingering shower activity hanging around. Any precipitation will quickly diminish through the early morning hours and dry conditions will prevail though much of the week. Lighter winds in the morning will become more southwesterly going through the day as a broad upper level ridge takes over and holds through the middle of the week.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Extreme Heat Watch from Tuesday afternoon through Tuesday 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.