textproduct: Detroit/Pontiac

KEY MESSAGES

- An Extreme Heat Warning remains in effect through 8 PM Thursday, with high temperatures reaching the mid to upper 90s and daily heat indices at or above 105 degrees.

- A marginal risk of isolated severe thunderstorms continues this evening, north of M-46. - Friday will also be hot and humid with high temperatures in the lower to mid 90s, but coverage of thunderstorms increases during the afternoon and evening hours; a marginal risk for severe thunderstorms exists across most of Southeast Michigan Friday.

- Showers and thunderstorms will continue at times over the weekend as a marginal severe risk persist on Saturday; isolated flooding will also be possible.

- A gradual cool down gets underway on Saturday, with highs finally dropping below 90F on Sunday.

DTW THRESHOLD PROBABILITIES

* None

PREV DISCUSSION

Issued at 359 PM EDT Wed Jul 1 2026

DISCUSSION...

The upper level pattern is evolving as anticipated today with 500 mb height anomalies on the order of +10 to +12 dam in place over Southeast Michigan. This heat dome stems from a governing anticyclone now centered over the Heart of Appalachia, marked by a central geopotential height of approximately 597 dam. Although high temperatures will likely come up a bit short today (mid 90s), dewpoints have overachieved (upper 70s) which keeps heat indices near forecast. Widespread +100F HIs were already reached prior to noon, and dewpoints have been slow to mix out this afternoon. No changes to the Excessive Heat Warning for the rest of today or tonight.

A bowing segment of storms maintained form and intensity crossing Lake Michigan and northern Lower. The southern end of the line was able to survive into the CWA, clipping Bay and Huron Counties. Modified PoPs accordingly to account for what remains of the storms testing the instability gradient. Activity should exit into Lake Huron by 21Z. For tonight, lows should easily challenge record warm minimums for July 2nd as readings only retreat into the mid or upper 70s. A low-end risk exists early Thursday morning for storms over the northern edge extending from upstream convection over Wisconsin. Low confidence exists for another southerly push from an initial eastward trajectory.

Given the slight eastward drift in the longwave ridge, and a cluster of upper lows/VortMaxes centered over northern Ontario/southern Hudson Bay, a broad region of enhanced westerlies positioned between the features sags slightly southward over Lower Michigan Thursday. This leads to improvement in shear (+30 knots 0-6 km), more so for the Tri-Cities and Thumb regions. The cap should weaken with time which supports Chance PoPs across the rest of Southeast Michigan by Thursday evening, but CAMs are highly variable in CI. Severe threat will be highly conditional. Should storms develop, SBCAPE values of 2-3 kJ/kg will support rapid updraft development and intensification. SPC SWODY2 highlights a wind and hail threat across the CWA. Temperature-wise, the gradient will be a bit more defined with lower 850 mb temperatures over the northern half than the southern half of the area, but still expect area-wide apparent temperatures back into the 100-105F range.

The airmass will gradually trend more favorably for convection into the back half of the week and into the weekend as the humid airmass stays locked in while subsidence wanes with the weakening/retrograding ridge. Models show potential for broader coverage of storms Friday afternoon and possibly overnight, dependent on both the track/evolution of upstream MCSs and timing of the diurnal adjustments to instability. Latest consensus model data suggests potential remains for heat indices to break 100F again Friday. The main question will be whether to extend the current Excessive Heat Warning, or to add a Heat Advisory to the end. A decision will likely be made before the expiration of the current headline tomorrow evening.

Deeper column moisture will support increasing rainfall rates over the weekend, but the complexity of the mesoscale-driven environment muddies any details on timing. Weak surface low Saturday night into Sunday as a shortwave trough helps guide a change in atmospheric state. Winds to flip northwesterly Sunday with a chance for highs to drop into the 80s.

MARINE...

A hot and humid air mass resides over the region today and through the rest of the week. Prevailing wind remains from the south and southwest at 10 to 15 kt with gusts generally capped around or below 20 kt due to higher stability over the relatively cooler water. The heat dome will maintain very low chances for precipitation for Lake St. Clair and Lake Erie, but Lake Huron will reside near the edge of the cap which offers potential for multiple rounds of thunderstorms tonight and Thursday. Isolated severe thunderstorms will be possible, capable of producing wind gusts in excess of 50 kt and large hail. The cap migrates farther south by Friday which brings higher chances for storms to the rest of the region. A cold front then sags south on Saturday, bringing a wind shift to the north and maintaining the potential for scattered to numerous showers and storms.

CLIMATE...

Daily Records for this week...

Detroit Record High Record Warm Minimum 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 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 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.