textproduct: Detroit/Pontiac

KEY MESSAGES

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

- Little to no relief is offered at night 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.

- There is a low chance for thunderstorms during the week, mainly toward the Tri Cities and Thumb. Potential then increases across all of SE Michigan during the weekend.

DTW THRESHOLD PROBABILITIES

* None

PREV DISCUSSION

Issued at 358 PM EDT Tue Jun 30 2026

DISCUSSION...

Excessively hot and humid conditions are taking root across Lower Mi this afternoon, on schedule to remain entrenched over the region through the mid week period. Afternoon observations indicate temperatures rising firmly into the lower and mid 90s combined with surface Td in the mid to upper 70s for heat index exceeding 105 at numerous reporting stations as of this forecast issuance. The Extreme Heat Warning then remains in effect as temperatures barely drop back below 80 tonight. These warm overnight lows make it even easier for day 2 of this event to unfold Wednesday afternoon. Guidance high temperatures in the mid 90s to near 100, and peak heat index of 105 to 110, are easily within reach assuming minimal potential for cloud or storm disruption of temperatures through Wednesday afternoon.

The brief flare-up of a few showers earlier this afternoon in the Thumb illustrates the typical uncertainty on convective trends in these hot and humid air masses. Surface Td in the upper 70s toward the Tri Cities and Thumb allowed a brief updraft to sneak past the 21C 800 mb cap shown in the 12Z DTX sounding. This occurred as boundary layer moisture mixed out with peak heating and could result in another stray shower or storm until early evening.

Also a consideration for thunderstorm potential is the close proximity of the MCS track across the northern Great Lakes over the next several days. For tonight, a vast majority of hi-res models among the HREF and REFS carry the next round of surface based convection from along the upper Midwest cold front into the U.P. and northern Lower Mi, guided by the SW to NE mid level flow. Low level jet forced nocturnal convection has a similar origin and track following along the west edge of the cap formed by the mid level thermal ridge centered over Lower Mi. The ARW and NAM suggest some tendency for late afternoon Midwest storms developing toward central Lower Mi this evening, a lower probability outcome considering the greater cap strength farther into central Lower Mi. There is a slightly better chance of surface based storms grazing the Tri Cities Wednesday afternoon, again judging by HREF and REFS members along with a survey of model soundings that show the cap even more vulnerable there during afternoon peak heating.

Day 3 of extreme heat and humidity then holds across the region for Thursday, although subject to even greater potential for disruption due to storms and/or cloud debris. As it stands in today's guidance, high temperatures make another run toward 100 across metro Detroit and at least the mid 90s toward the Tri Cities and northern Thumb. There is support for leaning toward the lower end of the temperature guidance range as deamplification of the larger scale mid/upper air pattern is already underway by Thursday afternoon. However, the 105 degree heat index threshold for the Warning remains easily reachable. A drop off peak is more likely by Friday as the long wave pattern transitions to an even more zonal configuration across the northern tier of states into the Great Lakes. Assuming no downward revisions to guidance, then the Warning may need to be extended into Friday for the Detroit metro area and drops off to Advisory along and north of I-69. An Advisory transition is possible for the entire area when factoring in a greater influence of storms and/or debris clouds as the stalled surface front wavers across northern Lower Mi. Prospects for an air mass change increase during the weekend as the northern Great Lakes front makes a move toward the Ohio valley. Today's 12Z extended range models offer solutions that bring the front into southern Lower Mi Saturday and south of the Ohio border by late Sunday. This timing is dependent on northern Ontario surface high pressure building adequately southward with a boost from the blocking mid/upper level ridge and a more uncertain southern stream short wave ridge reaching the Midwest by that time. For now, temperature guidance softly reflects the potential cooling trend with highs in the mid to upper 80s by Sunday and Monday.

MARINE...

A hot and humid air mass resides over the region today and through the rest of the week. Prevailing wind will be from the southwest at 10 to 15 kt with gusts generally capped around or below 20 kt due to increased stability over the relatively cooler water. The heat dome will maintain very low chances for precipitation for most of the area, but northern Lake Huron will reside near the edge of the cap which offers potential for several rounds of thunderstorms this week. Low confidence exists on timing, but the favored windows for storms appear to be centered on tonight and Wednesday night. Severe thunderstorms will be possible, capable of producing wind gusts in excess of 50 kt and large hail. The cap migrates farther south by late week which brings higher chances for storms to the rest of the region by Thursday and Friday.

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 until 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.