textproduct: Detroit/Pontiac

KEY MESSAGES

- Hot and humid conditions will persist through Friday afternoon.

- Scattered to numerous thunderstorms are forecast from late tonight through Friday night. There is a chance for strong to severe storms through this period.

- Locally heavy rain and minor flooding is possible late Friday and Friday night due to thunderstorms.

- While temperatures will be a litter cooler this weekend, the chances for showers and thunderstorms, with an isolated risk for strong to severe storms, will continue Saturday and Sunday.

DISCUSSION

The 596dam ridge centered over the central Appalachians continues to drive heat and humidity across Se Mi. Over the next couple of days, mid level height falls across ern Canada and numerous convective complexes and associated short wave features across the Upper Midwest/Great Lakes will suppress the ridge slightly southward. This will result in an overall cooling trend over the next couple of days, although shower/thunderstorm chances will be on the increase.

After convective outflow drove a little drier air into the boundary layer across portions of the northern counties this morning, diurnal heating and advection under SW flow still drove heat indices into the mid 90s to low 100s over most of Se Mi this afternoon. Recent ACARS soundings continue to suggest much of Se Mi is fairly well capped. Departing mid level short wave features across the thumb and southern Lake Huron this evening may cause some localized weakening of the cap, thus supporting the risk of some isolated convection in these areas. There is also some concern that the ongoing convergence axis near the Indiana border may support some localized weakening of the cap south of the I-94 corridor this evening. Otherwise, short wave ridging/negative vorticity advection in the mid levels will continue to suppress convective development across most of Se Mi this evening.

Sustained convective development is forecast across the upper Midwest tonight as nocturnal low level inflow intensifies. Corfidi vectors and thickness diffluence suggests a quasi stationary or regenerative MCS upstream. However, hi res solutions indicate several short wave impulses allowing for some forward propagating convective elements into Lower Mi. Forecast 0-3km MU CAPE up to 2500 J/kg as a result of the steep mid level lapse rates will warrant an isolated severe risk out of any overnight storm.

Based on various probabilistic temperature guidance, the excessive heat warning was extended through Friday along/south of I 69. The expectation is for a heat advisory to be issued for the Saginaw Valley and thumb region once the current warning expires. Given uncertainty on convection timing and coverage, there is the possibility that the night shift or Fri morning shift may have to make some additional adjustments to these heat headlines. Per several hi res solutions, building instability during the day Friday will support ML CAPE values up to 2500 J/kg across at least the south half of the forecast area. This degree of instability with 0- 6km Bulk Shear values around 25 knots will warrant a risk of strong/severe storms. Subtle cooling in the mid levels will weaken the cap. This and inbound short wave features will aid in convective development Friday afternoon into Friday night. The west-east orientation of the low level baroclinic zone and steady feed of moisture and instability raises the potential for training convection and thus locally heavy rainfall.

Short wave amplification is forecast across the western Great Lakes over the weekend. There remains ample spread among the model suite and ensemble members with respect to the timing and amplitude of this wave. This leads to considerable uncertainty as to precise timing of convection across Se Mi. The will result in an overall high pop forecast this weekend, although there is likely to be dry periods. Weak to moderate instability will warrant a risk of strong/severe storms through the weekend.

MARINE

High pressure remains nearly stationary over the southern Appalachians through the late week, maintaining a feed of a hot and humid air into the Great Lakes. Prevailing wind remains from the south and southwest at 10 to 15 kt with gusts generally capped around or below 20 kt. Isolated storms are possible through tonight, mainly around Lake Huron, but stable conditions across the region keep the probability low. An uptick in shower/storm coverage is forecast Friday and this weekend as the cap weakens and the predominant storm track shifts south. Isolated severe thunderstorms will be possible, capable of producing wind gusts in excess of 50 kt and large hail. A cold front sinks south on Saturday, bringing light north to northeast wind that tends to veer east by Sunday.

HYDROLOGY

Clusters of thunderstorms are forecast to develop Friday afternoon into Friday night. While there is some uncertainty as to the location of the more persistent thunderstorms, current forecast indications are that locations south of the I-69 corridor have the better potential for thunderstorms. If thunderstorms do development, they are most likely to become oriented west to east with a good chance for storms to train over the same area. There is expected to be a wide range in rainfall totals across the region. localized areas of one inch or more of rain is possible in areas that see the persistent thunderstorm activity. Rainfall rates in these areas are likely to reach 1 to 2 inches per hour. If these storms set up over urbanized areas, localized flooding is possible. Additional periods of showers and thunderstorms are forecast Saturday and Sunday, which will add to rainfall totals. Higher amounts will again be localized.

PREV DISCUSSION

Issued at 1252 PM EDT Thu Jul 2 2026

AVIATION...

A broad area of high pressure centered on the SE States continues to funnel hot and humid air into Lower Mi today. Part of the building daytime heat was a few hours of late morning MVFR cumulus that struggled to produce a ceiling and is now mixing into regular scattered coverage for the afternoon. Details on thunderstorm potential also remain elusive in terms of timing and coverage, especially since the morning outflow boundary washed out before producing any new convection. There is a low chance for lake breeze focused convection this afternoon and evening, and then a late night time window during which storms from the Midwest move in while dissipating. It is still best to add a storm mention in later updates should a trend solidify predictability. Conditions are otherwise VFR this afternoon through tonight and Friday morning.

D21/DTW Convection... There is an isolated thunderstorm potential for the D21 airspace this afternoon and evening, and again late tonight and Friday morning.

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorm potential this afternoon through Friday morning.

* Low for ceiling 5000 ft or less this afternoon and evening.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Extreme Heat Warning until 8 PM EDT this evening for MIZ047>049- 053>055.

Extreme Heat Warning until 8 PM EDT Friday for MIZ060>063-068>070- 075-076-082-083.

Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None.