textproduct: Detroit/Pontiac

KEY MESSAGES

- Hot and humid conditions arrive Monday with highs in the low-mid 90s and heat indices nearing or briefly exceeding 100 degrees.

- Extreme Heat Watch now in effect Tuesday to Thursday with highs to reach mid-upper 90s to 100 degrees and heat indices in excess of 105 degrees each day. There will be little nighttime relief with lows in the mid 70s each night.

- Hot and humid conditions extending to Friday into the holiday weekend with potential for showers and thunderstorms.

DISCUSSION

Main story remains the extreme heat that is expected over the upcoming week. Ridge amplification gets underway today into tonight. Locally today, surface high pressure will maintain stable conditions through the remainder of the day as heights build leading to the jump in temperatures this afternoon into the mid 80s. The light E-SE wind holds dewpoints generally in the 60s today.

Heat and humidity increase further Monday as the 594 dam upper level ridge builds across Great Lakes with the center nearing 600 dam centering across the Ohio Valley and Mid Mississippi Valley regions Tuesday through Thursday. While Monday will be noticeably warmer and more humid, early day clouds bring lower confidence in reaching heat indices of 100 degrees or more. Clouds and potentially light scattered shower/thunderstorm activity are associated with a passing mid level wave on the northern periphery of the inbound ridge. Data would suggest the locations with the best chance to achieve heat index values would be west of I-75 if enough clearing can happen early enough or greater coverage of clouds doesn't pan out. Have opted to hold off on any Heat Advisory for Monday given the lower confidence in occurrence and duration of Heat Advisory criteria.

Tuesday through Thursday and potentially into Friday will be the time period of most concern for extreme heat. Thus, have hoisted an Extreme Heat Watch starting Tuesday afternoon given the expected multi-day cumulative heat stress. An impressive airmass settles over the region as 850mb temps climb to 20+C and 700mb temps to 10+C and hold over the mid-week period translating to high temperatures in the mid to upper 90s. Wednesday and Thursday could possibly see urban areas of Detroit Metro region reaching 100 degrees as well. Combine that with the expected dewpoints in the low to mid 70s and heat index values should reach around or exceed 105 degrees across most of the area over several days. These forecast temperatures will be making a run at daily record highs and record warm minimums (see Climate section below). Positioning of the ridge at this time for the mid- week period should keep much convective potential out of southeast Michigan and confined to the north/northwest, which also increases confidence in the extreme heat. Convection potential is still worth monitoring in case conditions change.

Hot and humid conditions are likely to continue Friday into the holiday weekend. There is some data that suggests we could see an eventual broadening and flattening of the ridge over the Great Lakes by a series of shortwaves that could open the door to convective activity in the Friday time frame. Barring any widespread convective event, we could still be looking at temperatures in the 90s and dewpoints holding in the 70s.

MARINE

High pressure at the surface will keep the light northeasterly flow around through this evening. An approaching warm front will cause winds to increase slightly while veering to southeasterly tonight. This will hold through Monday as gusts reach 20 knots across Lake Huron. There is a chance of showers and thunderstorms to accompany the front especially across the north half of Lake Huron. By Tuesday morning, winds will have become southwesterly while again topping out around 20 knots. Though the gradient increases, stability also increases under a very warm airmass which will limit gust potential.

Daily Records for the Upcoming Week

Detroit Record High Record Warm Minimum Mon June 29 96 (1933) 77 (1945) 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 Mon June 29 100 (1934) 75 (1945) 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 Mon June 29 100 (1971) 75 (1971) 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)

PREV DISCUSSION

Issued at 137 PM EDT Sun Jun 28 2026

AVIATION...

Broad high pressure extending into the northern Great Lakes migrates eastward before becoming centered over the St. Lawrence Valley by Monday morning. A slight increase in heat and humidity this afternoon produces weak instability, enough for a high based SCT to BKN cumulus deck through the rest of the afternoon. These clouds wane this evening while high cloud from a remnant convective system arrives overhead. Prevailing east to southeast wind remains 10 kt or less through tonight. A warm front will then lift into the region from the southwest on Monday, marking the arrival of a much warmer and more humid air mass. There is the potential for a decaying cluster of showers and thunderstorms to ride in from NW to SE along this boundary mid to late morning - most favorable in the MBS vicinity where a PROB30 was introduced. Not enough confidence exists to include in the remaining TAFs at this time.

D21/DTW Convection... No thunderstorms are forecast through Monday morning.

DTW THRESHOLD PROBABILITIES...

* None

DTX WATCHES/WARNINGS/ADVISORIES

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