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 less hot and more seasonable this weekend, the chances for showers and thunderstorms, with an isolated risk for strong to severe storms, will continue Saturday and Sunday.

DTW THRESHOLD PROBABILITIES

* Medium for thunderstorm potential between 23z-04z this evening. Low for the rest of the TAF period.

* Low for ceilings at or below 5000 feet early this afternoon.

PREV DISCUSSION

Issued at 336 AM EDT Fri Jul 3 2026

DISCUSSION...

There's been a shift in the longwave pattern the last day or so with the strong upper low locked over central Canada shifting eastward and shearing out a bit across Ontario and Quebec. This in turn is flattening the ridge over the Great Lakes and forcing the highest heights southward as more zonal flow builds over the region. The resident heat dome will linger over the area one more day though increased chances of convection and additional cloud cover will lead to slightly improved conditions over the previous few days. This will also force the upper level jet southward across lower MI as well which will lead to high POPs and possible rounds of convection.

Residual heat across the region with 850mb temps around 20C and 500mb heights around 590dam will lead to another hot day. Overnight temps will again hold into the mid 70s which will help warm to the low to mid 90s once again. Dewpoints still in the low to mid 70s today as well will result in heat indices from about 95 (north) to 105 (south). Compounding effects of several days of excessive heat will make these slightly improved conditions for some location still dangerous. This lead to another Extreme Heat Warning being issued for most of SE MI. A few counties north of M46 are farther north of the outflow boundaries located across southern lower MI now so dewpoints and temps will be a bit lower and it was decided to go with a Heat Advisory for those counties.

Cooler temps are on the way for the weekend as convective outflows push the heat and humidity further southward. Highs will remain in the 80s through the upcoming week, dipping to the low 80s by Monday before rising back to near 90 by mid week. But dewpoints down into the 60s should make it feel more bearable.

As mentioned, convective chances are on the rise today and tomorrow as the jet axis drops over the region and outflow boundaries reside over the area as well. Unstable atmosphere with around 2500 J/kg of CAPE and some shear today around 20 knots (increasing to 30 knots Saturday) will help scattered storms get going along these boundaries. PWATs will be up around 2 inches and dewpoints in the 70s so plenty of moisture to work with, and as we saw in Chicago tonight, if storms can line up along a boundary we could get some flooding concerns due to heavy rain. Current activity tonight, though weakening, will help keep the boundary across the south to focus storms there. SPC Day 1 outlook highlights the state line with the SLight Risk area with Marginal across the rest of the area. Any storm could be strong to severe with moisture loading causing strong downbursts and storm tops around 50kft have been presenting some hail threat as well. CAMs are all over the place trying to produce storms and MCSs. Hard to put any timing into the forecast outside of stating the best timing looks to be first this morning across Mid MI tied to the convection west of Lake MI tracking up that way though should be weakening. Then most models have a weak mid level trough passing through this evening.

Long wave trough tied to the Low over Quebec will try to pivot down through the region Saturday keeping convective chances going though the day. Strongest instability should be pushed south of the state but models do still build around 2000 J/kg of CAPE with decent mid level lapse rates and some shear. So cannot rule out some stronger storms again.

MARINE...

A stalled frontal boundary is draped across the northern Great Lakes where it will remain over the next 24 hours before beginning to sink farther south on Saturday. To the south of this boundary is a warm and unstable air mass that will provide the fuel for scattered to numerous showers and thunderstorms today, tonight, and Saturday. Isolated severe thunderstorms will be possible, capable of producing wind gusts in excess of 34 kt. Prevailing wind will be from the southwest at 10 to 15 kt with occasional gusts to 20 kt in the shallower nearshore waters. As the cold front settles south on Saturday, wind direction will shift to north and northeast then veer east by Sunday. The unsettled pattern is likely to persist Sunday into Monday as a weak low traverses the region, but ambient wind magnitude is forecast to remain light.

HYDROLOGY...

Clusters of thunderstorms are forecast to develop this afternoon and tonight. 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.

DTX WATCHES/WARNINGS/ADVISORIES

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

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

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