textproduct: Detroit/Pontiac

KEY MESSAGES

- An Extreme Heat Warning is in effect Tuesday afternoon through Thursday for high temperatures reaching the mid 90s to 100 degrees and heat indices in excess of 105 degrees each day.

- There will be little nighttime relief as lows only cool into the mid 70s with heat index around 80 each night.

- Wednesday and Thursday are the hottest days, however hot and humid conditions also extend into Friday and the holiday weekend along with increasing potential for showers and thunderstorms.

DTW THRESHOLD PROBABILITIES

* None

PREV DISCUSSION

Issued at 250 AM EDT Tue Jun 30 2026

DISCUSSION...

Southeast Michigan now resides securely on the northern periphery of a sizable heat dome, as the large-scale pattern remains governed by a sprawling 594 to 596 dam subtropical ridge centered over the Ohio Valley region. Increasing depth and magnitude to southwest flow around the western flank of the ridge axis effectively encasing the region within a high magnitude thermal and moisture profile, as evident by a projected 850 mb temperature of 23-25c and a dewpoint encroaching on mid 70s at times. Net result remains a prolonged extreme heat event featuring near-record temperatures that gets underway today and persists through at least Thursday. An extreme heat warning is now active across the region for this window. Ambient afternoon highs will consistently surge into the mid-to- upper 90s, with a few locations testing the 100F mark. Combined with the elevated dewpoint, peak heat index values are forecast to range between 105 and 110F. Virtually no overnight relief anticipated within this environment as minimum temperatures struggle to drop below the mid-to-upper 70s. Risk for organized convective development remains very low across this period, given the highly capped environment and unfavorable positioning to witness convection growing upscale out of the Dakotas and upper MS valley and across the ridge periphery. A limited opportunity could emerge Wednesday across the Saginaw valley and thumb, with a subset of the model solution space initiating convection across northern lower during this time.

By Friday into the weekend, medium-range deterministic and ensemble guidance continue to suggest the long wave pattern will undergo a more notable shift. As the steering flow becomes more zonal along the international border, successive shortwaves rounding the northern periphery will gradually, yet effectively dampen, broaden and suppress the ridge axis into the Ohio valley. Potential for heat and humidity to remain elevated at least into Friday with the resident airmass slow to dislodge, before the downgrade in upper heights combined with increased convective potential likely yields more typical warmth and humidity for the holiday weekend. A more receptive underlying environment will exist now for convective development, but with the usual uncertainty at this time range regarding potential timing and scale with strong dependence on the mesoscale evolution upstream. Further refinement of precipitation chances are likely.

MARINE...

Wind gradually veers to southwest today, allowing a warm front to advance across Lake Huron today. As the hot and humid air mass builds in, the gradient will maintain SW wind of 10 to 15 kt today through Thursday, with gusts generally capped around 20 kt due to increased stability over the relatively cooler water. There will be a chance for thunderstorms over Lake Huron today as the front lifts through, but confidence is low on timing. Areas of fog may develop over the cooler open waters as well. Additional storms Wednesday and Thursday will be most likely to occur near northern Lake Huron where the prevailing storm track will set up along the edge of the more stable air to the south.

CLIMATE...

Daily Records for the Upcoming Week...

Detroit Record High Record Warm Minimum Tue June 30 96 (1931) 76 (2018) Wed July 1 98 (1931) 80 (1931) Thu July 2 99 (2011) 76 (2018) Fri July 3 100 (1911) 78 (1911) Sat July 4 102 (2012) 79 (1921)

Flint Record High Record Warm Minimum Tue June 30 98 (1933) 76 (2018) Wed July 1 102 (1931) 72 (2018) Thu July 2 100 (1931) 73 (2002) Fri July 3 99 (1921) 73 (1983) Sat July 4 102 (1921) 76 (1999)

Saginaw Record High Record Warm Minimum Tue June 30 99 (1964) 77 (2018) Wed July 1 103 (1931) 78 (1931) Thu July 2 100 (1931) 73 (2002) Fri July 3 99 (1966) 76 (1974) Sat July 4 97 (2012) 75 (2012)

DTX WATCHES/WARNINGS/ADVISORIES

MI...Extreme Heat Warning from noon today to 8 PM EDT Thursday 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.